SkyWatcher 90mm Mak unboxing

The Sky Watcher 90 mm Backpacker telescope that I ordered last week was delivered today. I wasn’t sure what all to expect in the box–the list of included items on Amazon is maddeningly unformatted and cuts off midstream. I thought I’d do a series of unboxing photos to document what’s in there for anyone who is considering buying this scope while it’s on sale.

Inside the usual plain-Jane shipping box is the actual product box with pretty pictures.

Inside that box are a backpack, the mount base, the warranty, and–yep–another box, all in their own plastic bags.

I was expecting to find the mount inside the backpack and the telescope inside the box, but I was wrong. The backpack contained the telescope tube–still swaddled in packing material in this shot–and the smaller boxes containing the accessories.

As with all the scopes I’ve bought new recently, the tube was wrapped in tissue paper to protect the finish, then cocooned in bubble wrap, then put in a plastic bag. Note the enclosed silica gel pack and “don’t blind yourself” warning tag.

Accessories, left to right: 90-degree prism diagonal (I was hoping for a mirror diagonal), 8×20 optical finder, and eyepieces. The eyepieces are 25mm, 12.5mm, and 6.3mm Plossls, all with silver barrels and stamped “Multi-coated”.

The back end of the scope, showing off the finish–which is insanely gorgeous–and the little descriptive plate with the scope’s specs. Note that the meniscus corrector plate up front is coated, not multi-coated or fully multi-coated (these are classes of anti-reflection coatings that improve light transfer through the scope; fully multi-coated is best).

Inside the smallest of the nested boxes: the mount, an L-bar adapter, the controller and cables. The L-bar was a nice surprise. Pictures of the assembled scope show the scope mating directly with the mount via its dovetail bar. The L-bar allows one to mount the scope upright instead of on its side, or to mount other devices with 1/4-20 mounting bolts, like cameras, binocular mounts, and other sport optics. Some thought went into the other accessories, too: there are a couple strips of sticky-backed Velcro so you can hang the hand controller on the side arm of the mount.

Everything set up, with an ink pen and the spare eyepieces (1.25″ barrel diameter) for scale. Note the leveling bubble on the mount. I was pleasantly surprised by the tabletop base. It looks plastic-y in pictures but it’s a nice big piece of aluminum with big rubber feet at the corners and a knurled hand-knob underneath for turning the 3/8″ bolt that goes into the bottom of the mount itself. That means the mount can go on any platform with a 3/8″ bolt, which includes most of the better photographic and surveyors’ tripods.

I had little time this afternoon and didn’t want to mess around with putting batteries in the mount and learning how to use it, so I put the scope on the Manfrotto CXPRO4 I use for museum photography and birding. This hall-of-mirrors shot is a typical view down the guts of a Mak. Incoming light passes through the meniscus corrector plate up front, bounces off the primary mirror at the back of the tube, then off the secondary mirror–not a separate piece of glass but an aluminized spot on the back of the corrector–then through a hole in the center of the primary mirror, then either straight into the eyepiece or, more commonly, off a mirror or through a prism that bends the light path by 45 to 90 degrees so you can look down to observe instead of crouching behind the tube to peer through it. The white dot farthest in is my ceiling light coming down through the translucent dust cover on the vertically-facing eyepiece. If you got lost among all of those reflections, no worries–see the ray-tracing diagram for a Gregory Maksutov here.

Outside, ready to go. Note the purplish color of the meniscus, caused by the magnesium flouride anti-reflection coatings. On refractors, the best fully multi-coated lenses look like dark-green holes, they just swallow incoming light like you wouldn’t believe. From what I’ve seen and read, catadioptric scopes like Maks tend to have correctors that are almost invisible if they have top-of-the-line coatings. This less well coated corrector shows some reflections, but in truth the difference is slight, just a few percent of the total incoming light. To see some photos of the correctors on other 90mm Maks, including a Questar, see Ed Ting’s 3-way comparo here.

I was all set up to take some pictures of the male hummingbird who sits in the top of our neighbor’s tree, but the little sod must be psychic. Every time I got the camera settings right and the camera to the eyepiece, he’d fly away. My time was limited and eventually I had to give up and go do other things. You can see some birding photos I got through my old Orion 90mm Mak, including what might be the same hummingbird, here.

I knew from the online UPS package tracker that the scope was coming today. For the past week, Weather Underground was predicting clear skies tonight. But sure enough, the New Scope Curse struck, and about sunset the sky went from a few scattered clouds to completely socked in. So the only views I got through the scope today were of a distant treetop to get the finder aligned, and a few seconds’ observation of that rotten hummingbird. Everything looked good and I didn’t see any obvious problems, but starlight will be the real test, as it is for any scope. Not tonight, unfortunately!

In lieu of a first-light report, here’s what I learned from the unboxing and my few minutes outside with the scope:

HOTS:

• The scope is real purty. Fit and finish are very nice.
• Mechanics seem good. Focusing is smooth with no detectable backlash, at least at the low magnifications I was using during the day. Stay tuned.
• Given my extremely limited time out with the scope, the optics seem fine. At 50x with the 25mm Plossl, I was counting scales on a tiny pollen cone in the top of a tall pine tree half a block away. I had no problem focusing directly to a crisp image, without having to flop around on either side of focus until I got it right–again, under the forgiving, low-mag conditions I was using it in today. No false color detected, but I haven’t really put it to the test yet.
• I haven’t used the supplied mount yet, but it gives a reassuring impression of solidity and has some nice touches I didn’t expect, like the built-in bubble level, included L-bar adapter, and Velcro strips for hanging the hand controller from the side arm.

NOTS:

• I’m disappointed that the diagonal has a prism rather than a mirror. Mirrors tend to be much sharper, especially at the high magnifications Maks are capable of delivering. Now, most Mak spotting scopes come with 45-degree prism diagonals so this one isn’t behind the curve, it just seems weird that essentially all Mak-makers (Questar excepted, obviously) hobble their scopes as shipped with inferior diagonals.
• I knew this coming in, but the supplied finder is tiny, and uncomfortable to use since I have to crouch behind it. Unfortunately I don’t have the 6×30 RACI anymore that I used to use with my little Maks. For review purposes I will use the supplied finder, but when it’s just me using the scope for pleasure I am either going to have to move the 9×50 over from one of my bigger scopes or buy another optical finderscope (or, just maybe, see if I can get along with dead-reckoning using a spare red-dot finder I have laying around). Also, the finder bracket is not one of the convenient two-bolts-and-a-spring models but an old-fashioned six-screw job, which means that getting the finder aligned takes about 5 times as long as I’m used to.
• The choice of eyepieces is odd, because each one is a factor of two away from another one. One of the most common astronomical accessories is a 2x Barlow lens, which effectively halves the focal length of any eyepiece. Eyepieces are often sold in staggered pairs to take advantage of this. For example, my first scope came with 25mm and 10mm Plossls, which when Barlowed gave me four focal lengths to choose from: 25mm, 12.5mm, 10mm, and 5mm. If they were similarly staggered, the three eyepieces included with this scope could have yielded six magnifications when Barlowed. Instead, they give just four: 25mm, 12.5mm (both natively and with the 25mm Barlowed), 6.3mm (both natively and with the 12.5mm Barlowed), and 3.2mm. So the 12.5mm eyepiece is superfluous if you have a Barlow. On the other hand, this bundle is clearly aiming for everything-a-beginner-needs-in-one-box completeness, and if you don’t have a Barlow yet, having three eyepieces is very convenient. Most other Maks come with just one (although some C90 packages come with two); advantage SkyWatcher.
• The optics are coated rather than multi-coated or fully multi-coated. I haven’t had a chance to see if this makes a detectable difference at the eyepiece. It only strikes me as odd because I have seen so many affordable Chinese-made scopes that are multi-coated that I had started to assume that was the new baseline.

I see that I went on at much greater length about the nots than the hots. Don’t read too much into that, it’s mostly whinging about accessories which are just as good as or better than those shipped with most other 90mm Maks. The only criticism that applies to the scope itself has to do with a level of lens coating that may not make much difference in actual practice. Remember that these are all first impressions; I have not yet had the scope out under the stars. Until I have done that and reported back, take this post for what it is: a list of parts.

More crazy scope deals at Amazon

I honestly can’t figure out why I haven’t blogged about this sooner. As happens from time to time, right now there are some screaming deals on scopes at Amazon. The two best are 90mm Maksutov-Cassegrains, a rugged, portable design that has been popular for decades.

The first is the Celestron C90. This scope has been around under the same name since the 1970s, but with three different designs. The first incarnation was a short, all-metal job sold in orange or black livery–you can see the orange-tube version I used to own on the left-hand tripod in this photo–that you focused by rotating the barrel, like a camera lens. The second incarnation was a longer, rubber-armored version more obviously intended to be used as a spotting scope, still with the rotating-barrel focusing mechanism. That one seems to have been discontinued just a few years ago in favor of the current version, which is a very attractive near-clone of the 90mm Synta Maks sold by Orion and SkyWatcher, with a more typical focusing knob at the back. There are differences among the models but they are mostly cosmetic, and the optics for all three brands are made by Synta.

This latest version is the one currently on sale at Amazon. I’ve been watching it for a while and prices have been all over the map, from a low around $140 to a high around $200. For reference, Orion’s StarMax 90 TableTop has an undiscounted retail price of $200 ($210 shipped) so for the sake of this post I’ll define a good deal as anything under $200. As of this writing the C90 is going for $172 with free shipping, which is a steal. UPDATE: OPT has this scope for $179.95 with free shipping right now (Feb. 26, 2012), so if Amazon is out or the price has gone up, check OPT. I’ve bought three scopes from OPT and the customer service has been outstanding, so I’m always happy to send them business. I know the scope is also on sale at other places around the web, but so far I haven’t found any deals as good as Amazon and OPT have on this scope–please let me know if you find a better one!

Most importantly, the C90 has gotten very good reviews, both at Ed Ting’s telescope review site and on Cloudy Nights. Some of the photos of Jupiter taken with these scopes are just astonishing–see this and this (NB: I think both of these are not single exposures but stacks of multiple frames, which brings out more detail).

The other crazy good deal right now is the Sky Watcher 90 mm Backpacker, which is the same tube as Orion’s Apex/StarMax 90 on a tabletop tracking mount. The mount can be put on top of a tripod to function as an alt-az head, just like the unmotorized mount on Orion’s StarMax 90 Tabletop, or you can pull the tube off and put it on the mount of your choice.

I haven’t used this mount so I can’t speak for it, but I’ve heard that it’s popular with daytime photographers because it can remember several pre-programmed points and slew to them on command, which helps people make panoramic photos and such. The tube I can speak for, because I used to own the Orion version, and it is a wonderful little machine, solidly built and typically with very good optics. (If you’re wondering why I don’t own that scope anymore, I sold it to buy a vintage orange-tube C90, sold that because the rotating barrel focuser was a pain to use at high magnifications, and since then I’ve been without a small Mak–until now!)

The SkyWatcher package is apparently on closeout. At least here in the States, SkyWatcher has been absorbed by Celestron (both are owned by Synta, who makes the gear) and the SkyWatcher-branded stuff is being phased out (as I predicted a couple of years ago). So this package might not be around for long. Right now it’s $179 plus $20 shipping, so for slightly less than the StarMax 90 Tabletop you get the same tube and a similar tabletop alt-az mount, only motorized and with tracking (not GoTo; the mount won’t find things in the sky for you, but if properly leveled and aligned it will track things once you find them), and 3 eyepieces instead of 2.

There’s one more scope I should mention: the Backpacker 80R has the same tracking mount with a wide-field 80mm refractor instead of a 90mm Mak. It’s a little lighter and a little cheaper at $155 plus $15 shipping. The refractor tube appears to be the same as Orion’s GoScope 80, which has gotten good reviews both on Amazon and at Sky & Telescope. Be aware of the significant design and performance differences between the 80mm refractor, which is specialized for low-power, wide-field views, and the 90mm Mak, which has a narrower field of view but much more capacity for magnification, especially on bright targets like the moon and planets.

Which of these scopes would I choose? Well, I ordered a SkyWatcher 90mm Backpacker earlier today, so there’s your answer. I’ll let you know how it works out. UPDATE: see these subsequent posts for the unboxing, first light, and some additional observations.

What if you read this post after all these deals are gone? Get one of the Orion tabletop scopes–the GoScope 80 (80mm refractor, $110 right now), SkyScanner 100 (100mm reflector, $110 right now), or StarMax 90 TableTop (90mm Mak, $200 right now). They’ve all gotten good reviews, the Mak isn’t that much more expensive than either of the Maks featured above, and the refractor is significantly cheaper (but lacks the tracking mount of the 80R).

One last thing: if you get a C90, don’t just slap it on a cheap photo tripod. It’s too heavy, and at the relatively high magnifications the scope’s long focal length delivers, the shakes will drive you crazy. Trust me, I hated my first Mak until I got a decent mount and tripod for it. You’ll need something like the Orion VersaGo II, Astro-Tech Voyager, Vixen Mini-Porta, or one of the nicer Bogen/Manfrotto units at a minimum, and these can easily set you back as much as the scope did in the first place. If you’ve already got a cheap tripod and two hundred bucks to spend, I’d go with the SkyWatcher unit or the StarMax 90 Tabletop. With their integrated mounts either one might work on top of your existing tripod, which only has to hold the unit up off the ground, and if it didn’t, you could still use it in tabletop mode while you save for a better tripod or whip up a homebrew (like this one).

Thanks to the folks in the Cats & Casses forum at Cloudy Nights for bringing these deals to my attention, and for the astrophoto links used above. The CN thread on these deals is here.

Cheap Scope Review: the Celestron FirstScope

My fascination with small, cheap scopes is probably obvious by now. Don’t get me wrong, I love my 10″ reflector, and if someone said I could only have one scope for the rest of my life, that would be it. But there is still something about wee little scopes that tugs at my heartstrings. I want to try out every one I come across, and see what it can show me. Partly this is an internal, personal fascination with small telescopes, probably akin to the fascination that some people have for very small trains or very small dogs. But it also has a social component. I do a fair amount of sidewalk astronomy, showing the moon and various other things to passersby, and I like to be able to recommend inexpensive telescopes to people. So I’ve been on a quest not only to find the perfect small scope for myself (a quest that is complete…for now), but also the perfect small scope to recommend to other people.

You might think those would be the same thing, but they’re not. If there is a posh end of the little tiny scope market, the SV50 is it. It’s a nice instrument–very sharp optics, within in the limitations of a 50mm f/4 optical train, a smooth focuser, and a rugged build. All this comes at a price. It was a price I was happy to pay, to get a scope that fit my peculiar requirements (being able to be stuffed into the bottom third of my backpack for long airplane flights to dark skies in other hemispheres), but for most people the SV50 is build quality overkill and optical underkill. For the same $150, you can get a 3 or even 4 inch scope on a solid mount, and those larger scopes are still nice enough to be all the scope that some people will ever need.

A few years ago the conventional wisdom–which can still be found in quite a few places out in the wilds of teh intarwebz–was that first-time scope buyers should avoid anything under $300. Then the recommended cutoff fell to $200. Then some manufacturers started building very well received scopes for $150, like the Orion StarBlast 4.5 (which is now up to $200, although you can get the tube alone for $150).

It’s not that there weren’t scopes available for less. Depending on your tolerance for plastic and frustration, the low-end department store scopes grade into toys that go all the way down to about a buck. But these were not in any sense “good” telescopes, and between bad optics and shaky mounts, standard department store telescopes have probably driven thousands of potential stargazers away from one of the most rewarding hobbies. For a long time, the minimum buy-in for a new telescope that actually worked as advertised was between $100 and $150.

That changed, bigtime, during 2009, the International Year of Astronomy. First there was the GalileoScope, which originally sold for $15 but nevertheless managed to attract plenty of good reviews and a strong following online. Galileoscopes are still available, although now that IYA2009 is over, the economy of scale isn’t working as well and the price has gone up to $50.

In the same year, Celestron released the FirstScope, a 3-inch reflecting telescope on a one-armed tabletop mount. The FirstScope was an official product of IYA2009 and was heavily promoted and ended up in a lot of places, including electronics stores and even department stores. It originally sold for $50, but the price has periodically been lower. As of this writing they are $45 with free shipping, but I have seen them as low as $36 online and people report finding them in Fry’s and other electronics stores for as little as $25. The box includes the assembled scope, two eyepieces, and a single sheet of instructions. As far as I know, it’s the most inexpensive, reasonably capable, complete telescope ever brought to the market. So naturally I was curious about it, and the combination of a temporary sale and an Amazon gift card put one in my hands for a while last year.

Let’s start with first impressions. This is a sharp-looking scope, right out of the box. It includes dust covers for the end of the tube and the focuser, and the two eyepieces come with plastic caps, and in general it has the same fit and finish of other mass-produced scopes. The tube is printed in spiraling script with the names of famous astronomers from the past, which I think is not only commemorative but also educational, in that people are supposed to read the tube, see names they don’t recognize, and go learn about them. The tension on the altitude axis is easily adjustable with a big knob that turns against a Teflon bearing surface. The mount turns easily on its base, and the base has three big rubber feet widely spaced for stability. No finder is included, but there are a couple of pre-drilled holes with screws for mounting one.

As usual with “tabletop” scopes, observing with the FirstScope may require some ingenuity if you don’t have an actual table handy. It’s small enough and the useful magnifications are low enough–more on this in a second–that you could just hold it by hand or cradle it in your lap. I used to prop mine on the trunk of the car, back when I still had a car with a trunk. The base is a big plus here–the three rubber feet give solid footing with no rocking, even on uneven surfaces, and the mount is small enough and strong enough that vibration isn’t a factor. The altitude and azimuth motions are also very smooth, so once you get something in the eyepiece, it’s generally pretty easy to keep track of it.

So far, so good; most cheap scopes are so wobbly and shaky that finding targets and then tracking them is an exercise in almost terminal frustration. Mechanically, the FirstScope is as smooth, steady, and convenient as any scope I’ve ever used, and that’s an unbelievable achievement in a bargain-basement scope.

Back to the ease of tracking things at the eyepiece: there’s the rub. How do you get the scope pointed at things, so that you can see them in the eyepiece? With most scopes, you point the tube in the rough direction of your target, look in the finder scope, center the target, and then go to the eyepiece. Without a finder, you’re down a step: all you can do is point the scope in roughly the right direction and hope for the best when you look in the eyepiece. With the moon this is almost foolproof; with anything else it can be surprisingly tricky. Admittedly, with the low power eyepiece the scope has a huge field of view, which makes acquiring objects somewhat easier, but I still found that observing anything other than the moon usually involved at least a little faffing about.

Once on target, how are the views? Here’s where you have to steel yourself to some unavoidable facts of optics and economics. First the optics: it’s dead easy to make a mirror whose surface is a segment of a sphere, all you have to do is rub two flat round pieces of glass together with abrasive in between and that’s the shape that emerges naturally. The problem is that a spherical surface doesn’t bring all of the parallel rays of light that fall on it to the same focal point. The shape that does is a parabola, which is not that hard to generate but still takes some extra figuring from the basic spherical shape.

Now the economics come in: for Celestron to produce FirstScopes at their target price point and still stay in business, they could not afford to parabolize the primary mirrors. That wouldn’t be a big deal if the focal ratio were longer. When the cone of light from the primary mirror to the focal plane is long and skinny, the rays converge well enough that past a certain point spherical mirrors perform just as well as parabolic mirrors. The Orion XT4.5 has a spherical mirror and most reviewers have been very complimentary about how sharp the views are. But the XT4.5 operates at f/8, meaning the light cone is eight times as long as wide (or to put it in more technical terms, the focal length is eight times the diameter of primary mirror). The FirstScope operates at f/4, which means a pretty steep light cone. Even parabolic f/4 systems are hard on eyepieces: it’s difficult to gather up that steeply angled light and turn it into a pleasing image. Without some kind of complex and expensive corrective lens, objects in the center of the field will be sharp but those toward the edge of the field take on interesting, compressed shapes, sort of like a photo taken with a fish-eye lens. With an f/4 spherical mirror, the visible aberrations are worse, and even objects in the center of the field may not be truly sharp.

This is in fact exactly what I found. I could see plenty of craters on the moon, but the views were fuzzy rather than razor-sharp. Jupiter would go from being an elongate smear on one side of focus to an elongate smear on the other side, but in between it never really settled down into a nice circle. The best I could get was a modestly flaring egg shape, although the moons on either side were easy to see. Stars went from being vertically elongated dashes to horizontally elongated ones without ever becoming nice round little points of light. And that was in the center of the field. Toward the edge, the stars became commas, parentheses, and seagulls.

Not only were the eyepiece views pretty underwhelming in terms of quality, they were also small. Economics again: a decent, well-corrected eyepiece with a comfortable apparent field, like a generic Plossl, costs about as much as the entire FirstScope package. The included eyepieces are a 20mm Huygenian yielding 15x and a 4mm Ramsden giving 75x. The Huygenian has a tiny field of view, like looking through a soda straw, but the views are at the sharp end of what this scope is capable of. The 4mm Ramsden has a wider apparent field, not as good as a Plossl but not entirely claustrophobic, but unfortunately 75x is really pushing what this scope can do. Orion packages their almost identical FunScope with 20mm and 10mm eyepieces giving 15x and 30x, and I think those are much more reasonable magnifications for this type of scope. Happily, the focuser accepts standard 1.25″ eyepieces so if you can use other eyepieces, and frankly almost any other eyepieces are going to be better than what comes in the box.

Regardless of what eyepiece you use, focus gets critical at fast focal ratios, because the steep angle of the incoming light means that the focal plane is extremely shallow. With a long light cone, the eyepiece travels through the comparatively long region where the light rays are almost imperceptibly out of line on either side of perfect focus, which means that you can adjust focus very precisely with reasonably big turns to the focuser wheels. With a steep light cone, even minute turns of the focuser can throw you from out of focus on one side to out of focus on the other. Sometimes the distance between visibly out of focus in both directions is less than the spacing between the teeth on a rack-and-pinion focuser, so the perceptible ratcheting of the focuser can throw you past focus. I also found this to be the case; the focuser had an almost imperceptible amount of slack which was greater in one direction than the other, so I had to deliberately overshoot the focus in the “bad” direction and then try to sneak up on it from the “good” one. If I went even a hair too far, I couldn’t simply reverse into focus, but had to go way past in the wrong direction so I could start sneaking up again.

Needless to say, this kind of monkeying around gets old pretty fast. It might have been worth it for reasonably sharp views, but not for a fuzzy moon or egg-shaped planets. I used my FirstScope off and on, halfheartedly, for a few months, and then passed it on to someone who was happy to get it.

PROS

• Extremely light and portable
• Solid mount with good motions
• Good fit-n-finish, comparable to what you’d get on much more expensive telescopes
• Visually attractive, commemoration of prominent historical astronomers is a nice touch
• Usable right out of the box
• Dirt cheap

CONS

• Almost zero instructions (in the box; more are available online, but for what telescope is that not true?)
• No included finder
• Included eyepieces are usable, but barely
• No provision for primary mirror collimation
• Very limited magnification potential
• Underwhelming image quality

It may seem mean to bring up these cons on a complete telescope that costs about as much as a cheap eyepiece. After all, fixing any one of them–adding a finder, or better eyepieces, or an adjustable mirror cell, or parabolizing the mirror–would drive up the cost, and then this scope wouldn’t be filling the same niche anymore. In fact, the telescope ecosystem includes a whole array of small reflectors that improve on the FirstScope in some way, so you can see what the upgrades cost. For $60, the Orion FunScope is virtually a clone of the FirstScope, but it adds a red dot finder, better eyepieces, and a socket in the base of the mount so the whole thing can be put up on a tripod. For $100, the SkyScanner 100 adds (in addition to the RDF, better eyepieces, and base socket) a parabolic mirror with twice the light-gathering area (but still no collimation), or the SpaceProbe 3 Alt-az adds (with RDF and better eyepieces) a full-size tripod, a collimatable primary mirror cell, and a longer focal length for more magnification and sharper images. And things go on up from there.

Still, somebody has to be at the bottom of the price ladder. Considering that it costs almost nothing, the FirstScope is actually a remarkable success. It is certainly not useless. It will show a lot of stuff, and I think it is much more likely to pull first-time telescope users farther into astronomy instead of driving them away like most department-store scopes–although the pull may soon be to a bigger or better scope.

Should you get one? Although I’m sympathetic to the design philosophy of the FirstScope, I’m going to recommend against. Here’s the deal: the Orion FunScope currently costs a full third more, but that full third is still only $15. Most people who can afford $45 for a telescope can afford $60, and the addition of the red dot finder alone (which sells for about $36 as a stand-alone item!) is worth the extra layout, in terms of the convenience it will bring to using the scope.

But honestly, I wouldn’t stop there. The FirstScope and FunScope are fine for getting your feet wet, or for having a well built (if optically wanting) small scope to play with, but I have serious doubts about how long they will hold most people’s attention. In my opinion, the next rung up ($100) is where the “keepers” start. What I mean by that is that the SkyScanner 100 and SpaceProbe 3 have good enough optics to be useful for a lifetime, and recently received very favorable reviews in Sky & Telescope. Even if you already have or someday move on to bigger scopes, they’d be worth keeping around as quick-look, grab-n-go, and travel scopes. Bottom line, if I got marooned on a desert island with a FirstScope, I’d grudgingly make the best of it, but if I got marooned with a SpaceProbe 3 I could probably keep myself happily occupied for the duration.

So what’s the final word? I think most people, even casual observers or kids, will be better served with a slightly more capable–but inevitably somewhat more expensive–scope. Nevertheless, I am glad that the FirstScope exists. It serves an extremely useful purpose: providing a rock-bottom entry-level scope that actually works.

Mission 20: Beta Monocerotis, a triple star

Mission Objective: Multiple star

Equipment: Telescope

Required Time: 10 minutes

Related Missions: Ring of Fire

Map to Beta Monocerotis, modified from the Monoceros constellation diagram on Wikipedia.

Hey look, I finally posted a new mission.

I’ve been slowly working away at the Astronomical League’s Double Star Club, and I just discovered this gem last week. It’s not the world’s easiest star to find. As a naked-eye subject, the constellation Monoceros, the Unicorn, is fairly dim and unimpressive. Beta Monocerotis is prominent in the western part of the constellation, just east of Orion and north of Canis Major, making a wide triangle between Sirius and Kappa Orionis (also known as Saiph, which is Arabic for “sword of giant”). I could just make it out with the naked eye from Claremont, hovering in the light dome over Los Angeles.

To fully appreciate this star’s charms, you’re going to want a telescope, but it doesn’t have to be a big one. I made my observation with my 80mm refractor, which has a focal length of 900mm (f/11). Using a 32mm Plossl eyepiece (28x), it was clearly a double star but not cleanly split (seeing was lousy). With the 12mm Plossl (75x) it was clearly split into a nice pair of equally bright gems. I decided to go up to 150x with a 6mm Orion Expanse, my favorite high-power eyepiece. So glad I did–at 150x, the southern member of the “equal pair” turned out to be a double itself, also of equally matched components! It was a nice surprise and a breathtaking sight, the three stars twinkling away at 150x.

I looked at dozens of photos, sketches, and eyepiece simulations of Beta Monocerotis while writing this post, and the image that come closest to capturing what I saw at the eyepiece is this sketch by Jeremy Perez, who kindly gave me permission to include it here. Jeremy is one of the authors of Astronomical Sketching: A Step by Step Introduction, and his website, Belt of Venus, has beautiful and evocative sketches of just about everything in the sky, from the moon and planets to deep sky objects and double stars. It’s definitely worth checking out, both to marvel at his work, and to get ideas for your observing wish list.

A poster on Cloudy Nights had this to say, “I just looked at Beta Mon last night in good seeing. What a neat thing. It reminds me of one of those antique mechanical solar system models.” I couldn’t agree more–it conveys exactly the same sense of mechanical precision and aesthetic appeal as an old-fashioned orrery.

If you’re going to catch Beta Monocerotis, you’ll need to do it soon after dark, because Monoceros is following Orion to the western horizon fairly early these days. Go have fun!

How to build a Dobsonian mount for a 5-inch telescope

INTRODUCTION

By reader request, I am posting instructions on how to build the Dobsonian mount shown in photo above. The design was made up mostly on the fly to suit my particular needs and the materials I had on hand. Your requirements might be different, so I’ll also discuss the design decisions I made along the way, so that you can a build a mount that fits your telescope and your needs.

If  you have the freedom to design a telescope from the ground up, you’ll be much better served by the free instructions provided by the Sidewalk Astronomers, or in any of the several telescope-making books out there. I’m thinking here of Build Your Own Telescope by Richard Berry, The Dobsonian Telescope by David Kriege (yes, that David Kriege, founder of Obsession) and Richard Berry, Sam Brown’s aging but accessible compendium, All About Telescopes, and several others. There are also some awesome resources online, including the Cloudy Nights ATM (amateur telescope making) forum, and plenty of solo ATMers who have posted pictures and descriptions of their designs on their own blogs or webpages (I like these, these, and this one in particular).

But as Rich Hoover said in a comment,

Most everything on the net is catered to 6″ or 8″ OTAs, so finding some GOOD plans for a 130mm OTA is rather difficult. Those plans that I’ve seen also make some rather large assumptions on the user’s part. It’d be great if there were plans with a complete parts/price list.

So it seems there is a need here, and I will do my best to address it–although the emphasis on GOOD plans might mean I’m doomed from the start!. I have zero experience with woodworking and anyone who knows what they’re doing will be appalled at the crimes against wood–and probably good taste–that I have committed. It is the height of ridiculosity for me to be instructing others in how to do this. Still, if you have some scrap wood, a saw, a drill/driver, no relevant experience and a desire to experiment, then you have everything I did when I started and you will probably do as well or, most likely, better.

Many thanks to David DeLano for much help along the way, and to Rich Hoover and Dan Walker for their continued interest in this project. Hope you find this useful!

PARTS OF A DOBSONIAN MOUNTED TELESCOPE

The first thing to do is to get familiar with the basic parts of a Dob mount. In addition to the OTA (optical tube assembly), there are three basic assemblies: the altitude bearings, the rocker box, the ground board.

The altitude bearings are attached to the OTA and allow the telescope to rock up and down. The rocker box is really the main part of the mount, and the one that requires the most design decisions and the most work to build. At the top end it provides bearing surfaces for the alt bearings, and at the bottom it rotates on the ground board via the azimuth bearing (which is not listed as a separate part because it is created by the rocker box and ground board). The ground board is the simplest piece, the easiest to build, and the hardest to screw up.

When we get down to the actual building, there will be separate sections on how to make each of the three pieces, plus separate sections on bearing surfaces and finishing the mount.

MEASURE TWICE, CUT ONCE

If you’re building a Dob mount for an existing OTA, the tube dictates everything else. So the first steps are to measure the tube, find its balance point, and decide how tall you want your mount to be. Only with these measurements in hand will you be ready to start cutting wood.

In my case, the OTA came from a SkyWatcher 130N-EQ2 setup. I bought this last summer on the cheap, and they’re still pretty darned good deals. However, I didn’t want the EQ mount, so I sold it and started building a Dob mount.

Finding the width of the rocker box. The OTA on this particular scope is 33″ long and 6.5″ in diameter (blue arrows). I decided to attach the alt bearings to the tube rings, which have 1/4-20 sockets, for simplicity (if you don’t have tube rings, you’ll have to build a box around the tube, like this). The tube rings add an extra half an inch on either side, bringing the width of the thing which must be mounted to 7.5″ (red arrows). But that’s not all–I also knew that I would be using thin plates of wood as bearing retainers to keep the OTA and alt bearings from slipping off their supports on one side or the other. The bearing retainers are each 0.25″ thick, meaning that the rocker box had to enclose a space at least 8″ wide (yellow arrows).  I wanted a little breathing room on top of that; I was using wide bearings so if the rocker was a little too wide, no problem, but if it came out too narrow, I’d have to start all over. So I made mine with an internal width of 8.5″ (white arrows), although in retrospect 8.25″ would have been enough.

Finding the height of the rocker box. Here you have a lot more freedom. The length and balance point of the OTA set the minimum height of the rocker box, in that you want the bottom end of the OTA to be able to swing freely all the way to vertical without bumping into the bottom of the rocker. On the other hand, you can make the rocker box as tall as you want, within reason. I wanted to make the entire mount as small and light as possible, so I went with the minimum height, and I’ll explain how I got there in a moment.

One persuasive reason not to make the mount as small and light as possible is that such a short mount will require you to either get down on the ground to observe, or to set the mounted telescope on some kind of stool or table. Neither solution is optimal for most people; getting up and down off the ground can be tiring and dirty (although some people aren’t bothered by either thing), and few stools or tables are stable enough to serve as observing platforms. Tiny flexings and rockings that are completely unnoticeable during normal daily use can be annoying or intolerable when magnified 200 times, which is what they’ll be when you’re observing at 200x magnification. If you want a mount that will be comfortable to use when seated, then park yourself in a chair, sit up comfortably, measure the height of your eyeball off the ground, and go from there. Remember that your seated  eyeball height should correspond to the maximum height of the eyepiece; it’s easy to bend over a few inches if the eyepiece is  lower, and hard to stretch up those same few inches if it’s too high. From your eyeball-to-ground measurement, subtract the length of the OTA from the focuser to the balance point, and knock off a couple more inches for the ground board and azimuth bearing surfaces, and that’s how tall your rocker needs to be. For an excellent example of a DIY Dob mount meant for seated observing, see Rob Nabholz’s Kid Peek II.

To find the minimum height of the rocker box, you have to know the balance point of the OTA. Please don’t do it like I did in the above photo! Three things are wrong in that picture: first, it was ridiculously dangerous to balance the OTA on a <1″ surface suspended over concrete. Do it on thick carpet, and balance the tube on a paperback book or something. You don’t have to be exact, and inch or so of slop in either direction is unavoidable. Which brings us to the second thing that is wrong with that picture: the balance point is way too far back because the scope is lacking the finder and an eyepiece. But in practice you will have a finder, maybe more than one, and an eyepiece. So load up the front of the scope with whatever you will actually use on a night-to-night basis, and don’t forget to remove the dust cover from the front of the scope (the third thing I did wrong).

Finding the exact balance point down to the last micron is a lost cause, because eyepieces vary so much in weight. My lighest eyepieces only weigh 3 or 4 ounces, and my heaviest weigh over a pound. The entire OTA of this scope only weighs 10 lbs, so changing the weight at the front end by up to a pound is going to shift the balance point, bigtime. If you do as I did and attach the alt bearings to tube rings, no problem, you can just scoot that ring fore or aft on the tube to rebalance (that’s a capability you might want to retain if you have to build a box around your OTA). Other ATMers use springs or adjustable friction thingamabobs, but remember, here at 10MA you’re getting caveman-level engineering. Speaking of, you’ll notice that I put the extra tube ring down at the bottom of the OTA, to shift the balance point backward and allow a shorter rocker box.

In fact, with the finder in place and a middleweight eyepiece in the focuser, the balance point on the tube was just aft of the halfway point, so about 16.5″ of tube would hanging down into the rocker box. I made my rocker with a height of 18″ so that the OTA would clear it even if I had to shift the tube down in the rings to accommodate a heavier eyepiece. If you’re going for a minimum-height mount, it’s worth erring on the side of caution. If the mount is an inch too tall you’ll never notice, whereas if it’s an inch too short you won’t be able to balance your scope without hanging extra weights off the front end. IMHO, it’s kinda silly to design a minimal mount that requires you add extra, nonfunctional mass to the OTA, although some people deliberately do this when the mount absolutely has to be small (to fit in to luggage, for example).

ALTITUDE BEARINGS

Loads of other telescope-building resources, including many of those linked above, will show you how to make elegant alt bearings. I’m going to show you how to make easy, cheap alt bearings. My alt bearings are 4″ grated PVC endcaps, which you can get at any hardware store for two or three bucks apiece. They’re held on to the OTA with 1″ 1/4-20 thumbscrews threaded through washers. I also put on alt bearing retainers to keep the scope from slipping sideways off the alt bearing surfaces. The alt bearing retainers are 7″ squares of 1/4″ thick wood, that I cut from disposable fish cutting boards that I found at Big Lots, half a dozen for a dollar. Any reasonably stiff, reasonably thin material would work; if all else fails you could cut two circles of corrugated cardboard and poke holes in the middle. I drilled the center holes in the bearing retainers with a 3/8″ bit.

In case it’s not clear from the pictures, the thumbscrew on either side goes first through the washer, then through the middle slot in the PVC endcap, then through the center hole in the alt bearing retainer, and finally screws into the 1/4-20 socket in the tube ring.

Total parts  and price list:

2x 1″ long 1/4-20 thumbscrews (~$1.50 for a pack of four)

2x washers (~$1.00 for a pack of eight)

2x 4″ grated PVC endcaps (~$2.00 apiece)

2x 7″ square alt bearing retainers (made from disposable cutting boards, $1.00 for pack of six)

Total cost: about $7.50.

ROCKER BOX

A rocker box minimally consists of four pieces: a front, two sides, and a bottom. You need the sides to support the alt bearing surfaces and thus hold up the OTA, the bottom to form part of the azimuth bearing, and the front to brace the whole thing and keep the sides from bowing or leaning under the weight of the OTA. So, at a minimum, all you have to do is build a four-sided box that matches the minimum internal height and width established above for your tube. Mine needed to have an internal width of 8.5″ and an internal height of 18″.

Rather than make a single front piece, I made three 8.5″-long braces. One connects the sides a little more than halfway up and sports a handle, and the other two sit at the bottom of the box  in front and in back. Whether you go with a single front piece or a series of braces, make sure that you don’t put them right at the top of the rocker, because you want the OTA to be able to swing down  to the horizon as well as up to vertical. I cut the braces from some 2.5″ wide x 7/8″ thick wooden bars left over from a broken futon, but just about anything would work.

The sides of my rocker box are 18″ lengths of an old wood shelf, 9 3/4″ wide x 5/8″ thick. Once you have cut the basic rectangle to length, the only necessary cuts are the V-cuts in the tops that will hold the alt bearings. I made these inboard of the corners a bit, to leave four flat surfaces on top. Partly because I didn’t want to stab myself if I fell on the mount, and partly because those flat surfaces made very handy supports when I turned the mount upside-down for finishing and for assembling the azimuth bearing (see below).

One thing I haven’t discussed yet is the effect of the V-cuts on the effective height of the rocker box. I made my V-cuts 4″ deep in the center, but obviously the alt bearing isn’t going to ride right down at the point of the V. It will ride higher up, at a point fixed by its diameter and the width of the V. By doing a little testing in advance I worked out that the 4″ PVC bearings sitting on some kind of bearing material (furniture sliders, as it turned out) would put the center of rotation back up at or near the top of the rocker box sides, and if you look closely at the top photo, you’ll see that that’s about where it ended up.

I had a 1.25″ spade bit that I was planning to make an eyepiece rack with, but in the end I used it to drill a bunch of holes in the side pieces of the rocker box. Mostly because I thought it would look cool. They probably help lighten the mount a little, although they also exposed more surface area for sealer and paint to bond to, so who knows. I’ll tell you this: if I had to do it over again, I’d leave out all the holes, because they made painting this thing a right sod.

The final piece of the rocker is the bottom, which on my mount is a 9″ by 9 3/4″ piece of 1/2″ plywood. It’s a little narrow, so the rest of the rocker partly overhangs it on either side. I could have gotten a bigger piece of plywood and cut a bottom that exactly matched the dimensions of my rocker (9 3/4″ long, fixed by the width of the shelf from which I made the sides, and 9 3/4″ wide,  fixed by the 8.5″ internal width plus 5/8″ on either side for the thickness of the rocker sides), but I already had an old plywood shelf that was 9″ wide. The bottom is screwed to the two lower braces anyway, and not to the sides of the rocker box; it’s really the braces that hold the whole thing together.

The rocker box is glued-and-screwed together. Get some long wood screws, drill pilot holes, do a test fit, put some wood glue on the surfaces to be bonded, and screw the thing together. If I can do it, anyone can.

Total parts and price list:

Braces: 2x 8 3/8″ long, 2 1/2″ tall, 7/8″ thick ($0)

Sides: 2x 18″ tall, 9 3/4″ long, 5/8″ thick ($0)

Bottom: 1x 9 3/4″ long, 9″ wide, 1/2″ thick ($0)

Wood screws (~$1.00 for a whole bunch)

Wood glue (~$4.00 for a good-sized bottle)

Total cost: for me, about $5.00, because I already had all the wood. If you don’t have scrap wood laying around, you could build a normal 4-sided rocker box (2 sides, 1 front, 1 bottom) entirely from 1/2″ or 3/4″ plywood. If you had worked out how big everything needed to be in advance, you could probably even get the hardware store to make the cuts for you. Or you could scavenge scraps from castoff bins and cut them yourself. Either way, it should still be possible to get out for under $10.

GROUND BOARD

This one is dead easy. You need a piece of wood big enough to support the bottom of the rocker box. You can make it a circle if you want to be fancy, or a square if you want to be simple. I cut a 10″ length of my 9″ wide plywood shelf and drilled a hole in the middle. For feet I used four 1″ diameter screw-in type furniture feet, which I found for a buck at Big Lots. In theory, three would be more stable because a 4-footed structure can rock on uneven ground. In practice, however, I found that the 3-footed version tended to tip toward the unsupported corners. I could have avoided that problem by making the ground board larger than the minimum necessary to support the rocker, but that would have made the whole mount wider and heavier. Do whatever suits your needs. Don’t screw in the feet until you’re done finishing the mount (see next section)!

Total parts and price list:

1x 10″ long, 9″ wide piece of 1/2″ plywood ($0)

4x 1″ diameter screw-in furniture feet ($1)

Total cost: about a buck, since I had the wood. Again, this is something you could cut out of any spare board or sheet of plywood.

FINISHING THE MOUNT

By finishing here I mean sealing, sanding, and painting, not completing. You can’t complete the mount without the bearing surfaces and so on, but you can’t put those on until after it’s painted. Painting is optional, but sealing is a good idea, because a working mount is going to dew up from time to time, maybe a lot depending on where you live.

Before sealing and painting I beveled off the top outside edge of the uppermost brace and put on a cheap drawer handle. The handle is a hollow U-shaped piece of plastic, like a very thick drinking straw folded back on itself. It’s threaded inside and the normal procedure would be to put bolts or screws through the thin front of  a wooden drawer and tighten them into the handle. I didn’t have that option, since I was going through a couple of inches of very hard wood. What I did instead was hammer in a couple of nails, liberally goop up the nails and the sockets in the handle with 5-minute epoxy, and then slide the handle down over the nails. Solid as a rock.

Also, I like nice smooth edges, so I sanded off all the sharp corners on the entire mount and ran little fillets of spackle along all of the joints. Totally optional.

At the suggestion of frequent commenter David DeLano, I sealed the mount with a mix of wood glue and water in equal measure, lightly sanding between coats. Then I gave it a couple of coats of water-based white primer, again with very light sanding between coats. I used Kilz2 latex primer, but anything would probably do. Since I was priming anyway, the sealing might have been overkill, but whatever. It was  cheap, didn’t take long, and if helps this thing last a little longer, great. Then two coats of black latex exterior house paint. I hate messing around with paint thinner so I did everything with water-based products.

Total parts and price list:

1x plastic drawer handle ($1.00)

Wood glue (same as above, for rocker box)

1 quart Kilz2 latex primer (~$6.00)

1 quart black latex exterior house paint (~$8.00)

sandpaper (~$2.00)

Total cost: about $17.00. Although I still have a lot of everything left over for future projects. If you count the fraction actually expended on this mount, it probably comes in under ten bucks.

BEARING SURFACES

Aye, there’s the rub: how much friction do you need or want on your bearing surfaces? Too much and the mount sticks or, worse, tips; too little and you can’t keep the scope pointed at anything long enough to see it.

The alt bearing surfaces were easy: I got four nail-in furniture sliders from Big Lots ($1.00 for the package) and, well, nailed ‘em in. They’re the little white nubs in the V-cuts. David had kindly sent some Teflon tape, but it proved too slippery for this mount. I could have scuffed up either the tape or the PVC bearings but went for the simpler solution instead.

The azimuth bearing surfaces are also pretty simple. From Rob Nabholz I got the idea to use furniture sliders against an unwanted phonograph record. Here you almost certainly do want just three, because even minimal rocking at the azimuth bearing is going to wreck the motions of your scope. Another one-buck package of sliders from Big Lots covered this and I have one left over for something else. Pound these into the bottom of the rocker box, as far apart as you can get them. The LP I got from the local library book sale for a dollar, but you could probably get one even cheaper at a garage sale.

To hold the stack together you minimally need a 2″ long 1/4-20 bolt, a 1/4-20 wingnut, and a couple of washers. I also like to put in some milk-jug washers to keep things turning smoothly. Milk-jug washers are a cinch: cut out flat circles from the walls of plastic milk jugs, and cut or punch holes in the middles so they’ll fit over the azimuth bolt. If your Dob, of any size, has sticky azimuth friction, you can stack up some milk-jug washers and/or old CDs around the azimuth bolt, between the ground board and the rocker, to take some of the weight off the lateral pads. You want the stack just thick enough to free up the motion a little, but not so thick that it makes the rocker box rock back and forth on the ground board (the only rocking normally associated with the rocker box is the rocking up and down of the OTA).  For this scope and mount, I found that one old CD and two milk jug washers were perfect.

This photo shows mount upside down, read to thread the bolt through. From the bottom up (top down in the photo), the bolt goes through:

1 – flat metal washer
2 – 2″ milk jug washer
3 – ground board
4 – record (glued to ground board)
5 – 5″ milk jug washer
6 – old CD
7 – 5″ milk jug washer
8 – base of rocker
9 – 2″ milk jug washer
10 – flat metal washer
11 – wingnut

The reason the wingnut goes on top is so that you can adjust the azimuth friction by simply reaching into the bottom of the rocker box and tightening or loosening it.

Total parts and price list:

7x Teflon furniture sliders, 4 in the V-cuts for the alt-bearing surfaces, and 3 on the bottom of the rocker box for the azimuth bearing surfaces ($2.00; $1.00 each for two packs of four)

1x old phonograph record ($1.00)

2x flat metal washers (from the same package bought for the alt bearings, see above)

1x 2″ 1/4-20 bolt (~$1.00 for a pack of three or four)

1x 1/4-20 wingnut (~$1.00 for a pack of four or five)

milk jug washers ($0)

Total cost: about $5.00, less if you have some of the hardware already lying around.

THE END

That’s it, the whole shebang. If you can use a saw and a drill, you can build this mount, and probably just about anything else you put your mind to. If I forgot anything or if any of the steps are unclear, let me know in the comments and I’ll do my best to fix it.

Total cost of the entire project: for me, about $25, since I already had the wood. If you have to buy wood, add another $5-10. Remember that you can find scrap wood all over the place; heck, your neighbor probably some in the back of his garage that he’d be happy to give you.

If you find this writeup useful, you are welcome, but of course not expected, to help support the site, and you can do so at zero cost to yourself. Here’s how. Thanks and clear skies!

Telescope tradeoff: aperture vs portability

In a comment on the last post, Jon Lindberg brought up some good points about the aperture/portability tradeoff with telescopes. It’s fertile ground for discussion, because there is always a tradeoff.

The big up-front ground rule for this discussion is that when it comes to portability, your mileage may vary. Some people consider 8″ or even 10″ scopes to be “grab-n-go”. For me, scopes break roughly into two categories: those that require one hand and one trip–my definition of grab-n-go–and those that require some more setup, either two hands or multiple trips or other fiddling. And at any given time, there is only one scope in each category that I’m using heavily.

Right now my big gun is a 10″ Orion dob. It weighs about 55 lbs assembled, which is about half in the tube and half in the base. I can move it while it’s assembled, but usually not without having a few twinges in my back the next day. So I usually carry the base to where it’s going to be set up, then put the tube on, then set up  some kind of  chair next to the eyepiece. Including a trip for my eyepiece case and some charts, it’s usually about four trips. But that’s okay, because I only tend to set it up when I’ve got some serious observing to do, or when I want to impress houseguests.

My old “big gun” was my first telescope, a 6″ Orion dob. It weighs about 33 lbs assembled, and I always carry it out in one piece. But it lives out in the garage with the 10″ and also requires a chair, so I’m still making two or three trips to get it set up. If I’m going to go to that much effort, I might as well get out the 10″ and get the benefit of nearly three times the light-gathering ability and almost twice the angular resolution. So I’ve barely used the 6″ at all since I got the 10″.

The 6″ is also facing competition from the other end, from my 5″ Skywatcher reflector on a homemade Dob mount. That one weighs just under 20 pounds and is short enough that I can use it sitting on the ground, so it’s more grab-n-go-able and still delivers most of the performance of the 6″ scope.

One of the lessons of all of this might be that I have too many telescopes. The more broadly applicable point is that the goodness or badness of a telescope for any particular application depends on what else you’ve got in the stable. When I only had one telescope, it was of necessity both my big gun and my grab-n-go scope. But my enthusiasm for hauling out a 30 lb scope on short notice declined markedly when I had something under 10 lbs to use for quick peeks.

But let’s get on to the meat of Jon’s question, which I am going to interpret as, at what point as you go down in aperture do you start noticing the compromises?

Again, the answer will be different for different observers. Some people think that anything smaller than 8″ is a waste of time. Obviously I disagree. I think that the vast majority of observers would say that a 3.5″-4″ telescope is probably at a threshold between noticeable compromise and being to see most familiar targets–moon, planets, Messier objects, the occasional comet–with rewarding vibrancy and detail. I base that in part on the massive commercial success of 90mm Maksutovs and 4″ refractors, especially apochromats. Also, some of the best deep-sky observers in the world like Stephen O’Meara and Sue French use 4″ refractors as their primary scopes.

That’s not to say that smaller telescopes aren’t popular as well. Refractors in the range of 60-80mm have always sold well and probably always will, especially short focal length, widefield scopes like Orion’s ShortTube 80 (pictured above). And you can have a lot fun pushing these little scopes to their limits, as Jay Reynolds Freeman did when he completed the Herchel 400 with a 55mm scope. But achievements like that get noticed because nobody expects to be doing serious deep-sky work with a tiny telescope. Sub-3″ scopes are almost always intended to be either introductory-level instruments or purpose-built grab-n-go and travel scopes.

So what’s the real word? My little SV50 is well into the realm of trading away performance for portability. So far it has shown every Messier object I’ve tried for, but all but the biggest and brightest have been faint fuzzies at the eyepiece, without a great deal of detail. And a scope that small absolutely requires dark skies to do any meaningful deep-sky work. Here in town it just doesn’t have the horsepower to cut through the light pollution. But that’s okay, because I didn’t get it to use here in town. I got it mainly for airline travel, and if I’m flying, it’s usually to someplace darker than the LA area, so it fills its very specialized niche admirably.

One thing that the little scope excels at is putting a truckload of stars in my eyes. Bigger scopes with longer focal lengths have smaller fields of view, that’s just an inescapable fact of optics. I’ve noticed that when I’m using bigger scopes I’m usually hunting for particular targets. With the SV50 I have a lot of fun just panning around the sky. It is the only scope that I have used that delivers the same super-wide field of binoculars, but with the advantages of being solidly and comfortably mounted (image crouching behind a pair of  mounted binoculars when they’re pointed at a target more than 45 degrees above the horizon) and having variable magnification.

For a little more than double the weight and volume, the C90 is still very portable and delivers a LOT more light and a LOT more detail. But for me it has two distinct disadvantages compared to the SV50. First, it’s just big and heavy enough to require a bigger tripod, so the whole kit-and-kaboodle won’t fit into a tiny bag that I can stuff into the bottom third of my backpack. So if I’m traveling with it, it becomes one of the focuses of my packing, instead of something I just shove in the bag and forget about until I reach my destination. Also, the folded light path gives the C90 a very long focal length for its size–900 mm–which makes reaching high powers a breeze. That makes it easy to power up on planets and specific deep-sky targets, but it also means that the scope has a fairly narrow field of view. So my mindset when I’m using it is more along the lines of, “what individual small thing am I going to look at next”, and not, “let me pan around the sky and see what I stumble across”. If you want the latter experience in a more capable scope than the SV50 that still only weighs about 5 lbs and is eminently airline portable, consider a Short Tube 80.

If you’ve got a little more space and don’t mind a little more weight, a 4″ Mak or a 5″-6″ Schmidt-Cassegrain will put a lot of aperture into a decently small space. Something like a Celestron C5 is about the size of a big coffee can but gives you enough light grasp and resolution to go after just about anything you want, especially if you have dark skies. The caveat I’ll add from my own bitter experience is that at this size of scope you have to put as much or more thought into the mount. When I got my first Mak, a 4″, I put it on a cheapo camera tripod from Wal-Mart. That was a disaster–the mount was so shaky that using the scope was an exercise in almost terminal frustration. Moving down to a 90mm scope didn’t really help, and my little scopes didn’t get much use until I got a decent tripod. And by “decent” I mean “costing as much or more than the telescope itself”.

I brought up the Short Tube 80 and all of the catadioptric scopes (Maksutov-Cassegrains and Schmidt-Cassegrains) first because they’re probably the most airline-portable of the bigger scopes. If portability is important but you don’t plan on flying with the scope, at least not regularly, the Orion StarBlast 4.5 and Edmund Astroscan both put some serious aperture into a one-hand telescope. Both are bulkier than a 5″-6″ SCT, but in both cases the bulk includes a base so you don’t have to worry about buying a separate mount and tripod (although you may want something, even a picnic table, to get them up off the ground). The StarBlast has better optics and a better focuser, but the Astroscan is almost indestrucible. As with any optics purchase, read around to find out the good and bad about them both before you make any decisions. The links to telescope reviews on the sidebar are good places to start.

Most telescopes are made in China and Taiwan these days, and the same models that are sold by Orion and Celestron in the US are usually available from SkyWatcher or Konus in the rest of the world. Happily, just about all of the scopes I’ve discussed can be had for $200-300 or even less if you’re willing to shop used (for example, at the Cloudy Nights Classifieds, where I’ve bought and sold just about all of my astro gear). If you have any questions, feel free to ask in the comments. I’m always happy to talk about telescopes.

UPDATE March 11, 2013: Here’s Doug Rennie’s StarBlast 6 hanging out amongst the flora–see comments for explanation!

 

Small telescope quest complete

When I caught the astronomy bug in the fall of 2007, my first priority was to get a decent scope. I spent about a month doing research in print and online and just about everyone said the same thing: get a cheap 6″-8″ Dob and some serviceable binoculars and start learning the sky.

This I did. My first scope was an Orion XT6 that I named “Shaft”. For two and a half years, Shaft was my workhorse scope.

But Shaft was still getting broken in when I decided that I needed something more portable. An XT6 is about 4 feet tall and weighs 33 lbs. It’s easy enough to  take the tube off the base and stow them both in the car for camping or a trip to the mountains, but I wanted a scope small enough to fly with. My parents live in rural Oklahoma under very dark skies and I knew all too well what I was missing here in the light-polluted swamp of California.

So began my quest for a grab-n-go scope. Not just any grab-n-go scope–some people consider a 6″ Dob to be grab-n-go. What I was really looking for was my “no excuses telescope”: a scope that would be so triflingly small and light, and yet so capable and easy to use, that I would never have an excuse not to have it along, whether I was driving up the mountain for a quick peek or flying to another hemisphere.

I’ve always had a thing for Maksutov-Cassegrains so my first venture was a little Mak, an Orion Starmax 102, that I picked up used. And it was a great scope. But I realized that a StarMax 90 would deliver most of the performance of the 102 but it would be a couple of inches shorter and a couple of pounds lighter (3.5 vs 5.5, if I remember correctly). So I got a Starmax 90, found it delightful, and sold the 102 (that’s my ad photo above).

The Starmax 90 was my small scope for a long time; it’s the scope I waxed lyrical about in this post. But I also thought that the old orange-tube Celestron Cassegrains looked pretty sweet, and I was entranced by the tank-like build and simple operation of the C90. Same aperture as the Starmax 90, but it was another couple of inches shorter. So I found a used one on Cloudy Nights and sold the Starmax 90.

The C90 has been a very fun little scope. It is even more rugged and versatile than I expected, and it fits in an insulated plastic-lined six-pack cooler, to boot. Nothing like getting an armored scope case for $5.99 at Wal-Mart (the black thing laying over the tube in the photo above is the finder, wrapped in one of the soft cloth bags that come over my wife’s favorite shoes).

But on some level I’ve known for a long time that the C90 would be at best a temporary stop on my quest for the smallest reasonably capable telescope. Because a couple  of years ago when I was surfing Cloudy Nights I discovered the Stellarvue SV50.

As I understand it, the SV50 started life as a high-end finder for larger telescopes, and one version is still sold that way today. I fully support that; one of my first upgrades for Shaft was a 9×50 finder that made star-hopping a lot easier. But people started using the SV50 as a telescope in its own right and it developed quite a following. It is now sold as “The Little Rascal”, a stand-alone spotting scope with a clamshell mounting ring, eyepiece, and in the latest guise, a carrying case.

My SV50 was a present to myself for finishing my summer teaching. I bought it from Oceanside Photo & Telescope on the last possible day that I could have done so and still have had the telescope delivered before I left for Uruguay. I was on the phone for maybe 5 minutes tops and in that time the sales guy (whose name I’ve unfortunately forgotten) answered all of my questions instantly and authoritatively, processed my order with admirable efficiency, and even managed to find me a discount I hadn’t known about. If that’s not good customer service, I don’t know what is.

This is a tiny, tiny scope. The aperture is 50mm, the focal length is 205mm, the magnification with the included 23mm eyepiece is 9x. So you could think of it as one half of a pair of 9×50 binoculars. Except that it’s not.

For one thing, it accepts any eyepiece in the standard 1.25″ barrel size, so you can vary the magnification. And it is really, really well made, as one would expect from StellarVue. There are binoculars out there that are made to equal or better specifications, and there are binos that have interchangeable eyepieces, but they’re out of my price range so they don’t come in to this story. And you can put it on a tripod and look at things directly overhead without breaking your neck.

Also, having had the opportunity to compare the performance of the SV50 with that of my admittedly low-end 50mm binoculars, the image in the SV50 seems brighter.  Possibly because it has fewer internal reflections to steal light from the path, possibly because it’s just a better made instrument, possibly because my binoculars are cheap. Whatever. I’m deliriously happy with the SV50.

The SV50 is 9.5″ long and weighs 1.5 lbs. By comparison, the C90 weighs 3.9 lbs fully loaded (i.e., with diagonal, eyepiece, and finder), and the Starmax 90 weighed 4.6 (the less said about the positively Brobdingnagian Starmax 102, the better). Crucially, this means the scope is light enough to ride comfortably on my little Manfrotto 785 tripod, which only weighs a couple of pounds itself.

And that’s good because the folded tripod is the same length as the scope, so it fits into a roughly equal space. I found a little travel shaving kit at Target that holds the scope, doubly wrapped in bubble wrap; the tripod; three eyepieces; the handle for the alt-az head that goes atop the tripod; my mini red flashlight (a mini Maglite painted over with red nail polish); and a small notebook and pen for recording observations. The only thing that doesn’t fit in the bag is the alt-az head itself, a DwarfStar from Universal Astronomics. Close enough, says me.

By comparison, the ~4 lb C90 and StarMax 90 require the beefier Manfrotto 190CXPRO4, which weighs 3 pounds and folds down to 21″. Which, okay, means you can still get away with scope, accessories, DwarfStar, and tripod for just under 9 lbs. But why settle for 9 when you can have 4.5? More importantly, I have not had the courage to put the bigger (and much more expensive) tripod in my carry-on luggage. For the love of Pete, I use a netbook as my primary computer because I hate carrying heavy stuff through airports. Anything that gives me adequate functionality at half the volume and mass, I will be on in a heartbeat.

For eyepieces I’ve been using the included 23mm eyepiece, yielding 9x; a 10mm Orion Plossl giving 20.5x; and a 6mm Orion Expanse giving 34x. At 9x the SV50 functions as its own finder and requires no other. At 20.5x the scope just gets out of the way and lets me observe. It is honestly one of the most hassle-free setups I’ve ever used. At 34x the optical train is starting to pant a bit. A focal ratio of f/4.1 is hard on eyepieces, especially widefields. The view is still acceptable but focus gets to be very touchy. Fortunately the built-in helical focuser is super-smooth, with no backlash, and is a real joy to use. At the end of the day the three eyepieces get rolled up in a Ziploc bag to fit into the small empty space between the scope and tripod.

So far my SV50 has only seen serious use away from home. In Uruguay I used it to do all of the observations for the Southern Sky Telescopic Club, and this weekend in Big Bear Lake I spent a pleasant hour chasing some Messiers. In fact, I’ve decided to re-observe all of the Messier objects with this scope. I don’t know how long it will take because it will absolutely require dark skies, which I don’t get to as often as I’d like, but I’ll just chip away at it as opportunities present themselves. In any case, I think my quest for the “no excuses telescope” has finally come to a happy end.

I don’t know what I’ll obsess about next, but if you stick around you’ll probably find out. Clear skies!

Evolution of the cheap scope

How it came to me:

How it looked about a month ago:

How it looks now:

The altitude bearings are PVC endcaps turning on pound-in furniture sliders. The azimuth bearing surface is more pound-in furniture sliders turning on a vinyl record. The whole setup weighs about 20 lbs, and delivers most of the performance of my 6-inch scope in a much more portable package. It’s a keeper.

Many thanks to frequent commenter David DeLano for advice on sealing and painting the wood, discussions on bearing surfaces, and some peel-and-stick Teflon tape that I ended up not using (too slippery, if you can believe that).

Cheap scope put to good use

You’ll recall that Amazon recently had a nice intro-level reflector on closeout for a stupid-awesome price (sadly they’re out now no longer stupidly cheap, just sorta cheap), and that I got one, sold the included tripod, and got to work building a new mount for it. After about three weeks of non-action, I finished the mount today, and took the scope downtown this evening to do some sidewalk astronomy.

It was fun, and funny. To me, this 5″ scope is small. Like, that’s why I got it–because I wanted the biggest scope I could carry around with one hand. But out in the wild, where most people’s only exposure to telescopes is by way of shaky 60mm department store horrors, a solidly mounted five inch scope is but a little lower than the Hubble. People thought it was HUGE. They gravitated, especially kids. We were down at the fountains for an hour and 32 people came by for a look at the waxing gibbous moon. The last person was the 1027th passerby to look through one of my scopes since I started doing sidewalk astronomy in the spring of 2009.

The moon was pretty great, too. And obviously I’m pleased with the scope.

Single 1/60th of a second exposure with a handheld Nikon Coolpix 4500 in macro mode, shooting through an Orion Sirius 32mm Plossl and a Sky-Watcher 130N Newtonian reflector.

While I was out…

May turned out to be a pretty eventful month for me, astronomically-speaking.

As noted in my oath-breaking last post, I bought one of the Sky-Watcher scopes that is on crazy sale at Amazon right now. I got the 130N-EQ2, a Newtonian reflector on an equatorial mount. I’m not a big fan of EQ mounts. Yeah, they let you track the sky by moving the scope slowly on one axis instead of two, but for that convenience you get to pay quite a bit more than you would for an alt-az mount (normally, that is; right now at Amazon you get the whole kit-n-kaboodle for about what the eyepieces regularly cost), and you get to lug around a lot more weight, too. YMMV, but I like to lug optics, not machinery, and I don’t mind nudging the scope every couple of minutes. So I sold the EQ mount on the Cloudy Nights classifieds (bringing the net cost of the scope down to a ridiculous $40) and used some scrap wood from the garage to build a Dobsonian mount. That project is still ongoing; it’s about halfway painted right now. More construction details soon.

Back in April, I started writing a series of articles on the world’s largest telescopes for Nightwatch, the newsletter of the Pomona Valley Amateur Astronomers, and the first one came out in the May newsletter (that link will be good for about three months, after which you’ll be able to find the article on the Nightwatch archive page).

Finally, and most excitingly for me, at 4:30 in the morning on May 25 I found and logged my final Messier object. The quest is complete! And one of my astronomical resolutions for 2010 is fulfilled. Two more to go…

What does June hold? Well, on the 12th the PVAA is going back to Mount Wilson. I’m keeping my fingers crossed for that–last year they got clouded out in June and had to reschedule for the fall (which worked out well for me). Venus, Mars, and Saturn are all well-placed right after dark, and Jupiter is up before dawn. There’s a minor comet to chase if you’ve got optics and reasonably dark skies. And I’m about 10 objects away from finishing my observations for the AL Deep Sky Binocular Club.

So, lots to do and see. My posting will probably be hit-and-miss this month also; I’m going on vacation for the next week and when I get back, I have to knuckle under and get to work on some lectures. If you need ways to entertain yourself, the advice given here still holds. Clear skies!