Archive for March, 2012


Going dark for a while

March 27, 2012

Hey folks,

I am sorry to say that I will probably be around much less frequently for the next two or three months. I have severely overcommitted myself this spring and for the next few weeks I have to pay a succession of pipers. I hope I can find little spaces here and there to post. I will certainly try, but no promises.

In the meantime, I’m happy to see that comment-thread conversations are rolling along just fine without me. I hate to take off when it feels like things are really hopping around here, but that’s the shape of life right now.

Before I go, here’s how David DeLano put his GalileoScope on his SkyWatcher 114N OTA as a superfinder, which itself has a red-dot finder. David was already working on this before I posted about homebrew finders, so I can’t claim any inspirational credit, it’s just a nice example using, in this case, some commercial rings David found on sale.

See you in the future!


SkyWatcher 90mm Maks sold out?

March 19, 2012

Seems to be the case. Amazon has no more, and neither do Adorama and OPT.

So what to do if you’re in the market for a little Mak? Get a C90, stat! As Ed Ting said in his 3-way Mak comparo, “An embarrassingly good telescope package for almost no money. As of this writing they’re practically giving them away. If you’ve been thinking about getting one of these, I urge you to do so immediately before they run out, or before Celestron stops making them.”

On one hand, there is probably little danger that Celestron will stop making them; they’ve had a 90mm Mak in their product lineup for almost as long as I’ve been alive. Now that the SkyWatcher brand has been subsumed into Celestron (both are owned by Synta), it’s likely that the SkyWatcher-branded stuff is being allowed to die off to strengthen the Celestron brand.

On the other hand, C90s have been around for ages in multiple guises, but they haven’t always been this inexpensive. I wouldn’t get one just because they’re cheap–that way leads to a garage full of telescopes–but if you already want a little Mak and you’re bummed that the SkyWatchers are gone, the well-reviewed C90 should be a more than acceptable substitute.

I haven’t posted any new observations with my little Mak in a while because it’s been raining here. Next weekend I’m out of town, so I was hoping to get out to the desert for a Messier Marathon this weekend. Naturally it rained all weekend and today dawned sunny and clear. So it goes.


Thinking about cheap finders–and cheap finder mounts

March 16, 2012

This all started because Orion’s Maks are “wrong-handed” for their VersaGo II alt-az mount. Here, I’ll show you what I mean. Here’s my Apex 127 on the VersaGo II.

If the scope is sitting on its dovetail bar, the dovetail shoe for the finderscope is on the left side of the scope, at about 10:30 (viewed from the eyepiece end). So when the scope is mounted sidesaddle on the VersaGo II, where the dovetail faces left, the finder ends up at about 7:30. The eyepiece of the finderscope is a bit below the eyepiece of the main scope (the effect is exaggerated in this picture, which was taken looking down at the mount). This isn’t terribly inconvenient, it just looks weird, and it can cause some slight balance problems when the scope is aimed up high.

What I’d like is to have the finder sticking straight out sideways from the scope. That way the eyepieces would be at the same height, and the altitude axis of the mount would run through the centers of mass of both scopes so there would be no balance problems. I could achieve that by moving either the dovetail shoe for the finder or the main dovetail rail, but that would require drilling holes in the scope and I’m not willing to do that. A better solution is just to get some tube rings, so I can orient the scope and the finder shoe however I want.

Thinking about that led me to think about how nice it would be to have a small refractor mounted alongside the 5″ Mak. Something in the 70-80mm range could function as both a “superfinder” and rich-field telescope, so on one mount I’d have a low-power, widefield scope and a planet-killer.

Stellarvue sells an 80mm superfinder that some folks use as a stand-alone rich-field and spotting scope, but that runs something like $250. I’m sure it’s nice, Stellarvue gear is top notch, but as always I am interested in less expensive options. Celestron’s Travel Scope 70 is not much smaller,  it’s gotten generally good reviews (at CN, for example), and it can be found for $60-80 (the Amazon price fluctuates a lot, but other vendors usually have it for $60). That would work for a finder, but I’d have to mount it somehow. I could just buy some mounting rings, but adjustable mounting rings for a 70mm scope would cost more than the scope itself. There has to be a better way.

So that’s the first thread: moving up from a 50mm finder without breaking the bank.

The other issue is that I have several scopes that I use regularly, and only one 9×50 RACI finder. So I keep moving the finder around, and this is kind of a pain, because I have to realign it for every scope. It would be nice to just park it on one scope, but that means I’d need finders for the other scopes. As before, I could just buy some more RACI finders, but the 6×30 models are about $60 and the 9x50s, which I really prefer, are $90 or more.

Now, I could build my own finder. I have spare 50mm objectives from some cheap binoculars, and I have an erecting prism diagonal, and I could build the tube out of plumbing parts. But that still leaves the problem of mounting, and as before, the mounting rings would set me back almost as much as a new finder anyway.

That’s the second thread: adding 50mm finders without breaking the bank.

It’s been a while since I’ve bought a new finder, and I have to admit that the prices kind of took me aback. I can’t shake the thought that the Celestron Travel Scope 50 runs about $45 and the Travelscope 70 is $60. If only I could find some way to mount them, I could have easily focusable luxury finders for less than new RACIs of smaller aperture! And that’s really the rub in both of the threads of thought outlined above: building a finder-quality scope is not hard. Mounting it solidly, reliably, and conveniently is hard. Part of what you pay for in a commercial finder is a sturdy, easily-adjustable finder stalk with a standard dovetail foot.

Well, what if I built my own finder stalk?

There are examples out there. My favorite, because they look easy to fabricate, are what I call the “half-pipe” mounts that consist of two half-cylinders mounted back to back. Here are a couple from the “Frugal Astronomer” thread on CN:

This one is by CN user Grendel, and is made from cardboard tube–as is the finder, as shown in this post.

I think this one is from the same thread, but derned if I can find the original post now. Anyway, it’s not my photo, I’ll credit it properly if I figure out where I found it,  if it’s yours please chime in, etc. The nice thing about this one is that it’s easily adjustable, thanks to the combination of thumbscrews through the half-pipe and rubber bands pulling the finder against them. Note the zip ties holding the half-pipe mount to the main scope.

So these got me thinking about the possibilities of the half-pipe mount. Here are some sketches I knocked up in GIMP.

The one at the top is simplest, just a V-slot, essentially the same as in the previous photo. The finder would have to be held in with rubber bands, elastic, velcro straps, or zip ties. Alignment could be done with bolts (you could either tap threaded holes or drill simple holes and epoxy nuts on the outside) or shims.

At lower left everything is the same except a trough has been added to cradle the finder, which might make it easier to use. I don’t know that, obviously, just kicking ideas around here.

At lower right is a full ring holder. I figured, if you’re putting alignment bolts through anyway, just make two more holes and you’ve got a six-bolt alignment system just like on the commercial rings (see an example in the photos here).

The key thing isn’t finder alignment, though, since even rubber bands and shims would work there. The key thing is convenient and repeatable mounting and unmounting to the OTA. I got to thinking: with an inverted V-shaped foot, like all of these have, is there any reason it coulnd’t be cut and sanded to fit into the existing dovetail shoes, so that the dovetail retaining screw tightens on one side of the inverted V? If that could be made to work, this kind of finder base could be mounted and unmounted and moved between scopes just as conveniently as one of the commercial jobs.

The end of all of this thinking? I got a piece of ABS pipe when I was at the hardware store to get parts for my sun funnel. I’m going to play around and see what I can come up with. If I find a workable solution, I’ll post it.


Guest post: Sun Funnel built and tested

March 14, 2012

Here’s something new–my first guest post on this blog. It’s by frequent commenter David DeLano, whose DIY astro gear I have featured here once before. David puts a lot of thought into equipping and fine-tuning his scopes to get the best performance possible, and you can see that attention to detail in his sun funnel writeup. He sent this as an email message with permission to post. It’s pretty much as sent, with just one or two additions to clarify things that were already familiar to me from our email conversations. The sun funnel parts list and instructions are here and here, and I previously mentioned it on the blog here. Enjoy!

First off, this is one of the coolest projects I have done lately.  It was easier than I thought, and the results were better than I would have expected.  Thanks for pointing it out!! [I didn’t put him up to that, promise!–MW]

Here are some experience points worth noting.

It was cool to have an EQ mount, even as light as this one is.  I had to do some tweaking on it, and it took several brain sessions to get it aligned properly, but one I got it configured, it helped to be able to tweak one knob to follow the sun.  It moves fairly quickly.  You get maybe a minute to look at any specific thing before you need to adjust the view.  I also had to tighten the Alt down most of the way.  This setup is very heavy on the EP end.  I had to slide the scope a bit back to clear the Alt micro stem, which made it even worse.  I need to find a counter weight to put on the front of the tube.

When you mount the screen on the funnel, make sure the back, inside, is as clean as you can get it.  I had an annoying spot on mine, and I ended up taking it apart, cleaning it, and putting it back together.  One of the directions says to put the shiny side inside the funnel.  I agree.  This side is easier to clean, as it’s slicker.  Try to keep the clamp as close to the top as you can, as it will want to slip down as you tighten.  After a while, though, the grabbiness of the cloth will keep it in place.  Pull the cloth down from under the clamp as you go, and try to eliminate any creases.  After a while, the sliding down will just tighten.  I tightened mine until I could ping the top like a drum.

I don’t have a shade yet, but what I’d suggest more is a shade umbrella or tent.  A beach umbrella clamped to the mount, or even a chair would be nice.  It gets hot observing the sun.  In fact, this is probably conducive to sitting in a chair to observe anyway, since you don’t have to be hunched over the EP.  The only part of the scope that got noticeably hot was the front of the funnel, from the outside, not the inside.

The Solar Scope

Pardon the leaves…that’s another project for this week.  This is a Bushnell 50mm F12.5.  The ideal EP is around 17.5mm, but the closest I have is 15mm (OWL), and it works fine.  Note that this diag is either 90* or 45*.  I didn’t try 45*, but that might be nice for sitting in a chair.

The Solar Finder

This is a nifty and very inexpensive solar finder that David came up with and described in a couple of previous emails. He wrote:

Something finally worked and was darn easy.

I took a clear-ish film canister, with a grey lid, and punched a hole in the center.  This was the hardest part.  I used my centering punch to fight the little nib and get a hole a close to the center as possible.  (If you don’t have one of these, get one.  They are cheap, and you can use them for all sorts of things.  You put the point where you want to mark and press down. It’s spring loaded and will “pop” when enough pressure is applied.  You are under control up until the pop, so you can’t miss making a small indent exactly where you want it.  Pop it several times to make a deeper dent.  I use this for starting screws, getting a drill bit to start where I want, etc.)  I ended up with a bit if a smile hole, but in testing it worked.  I did go back up and clean up the hole with a 1/16″ bit.

I bought two nylon spacers, zip tied them together, punched holes in the bottom of the finder, and put the spacer set on with a zip tie.  I zip tied the assembly to the end of the scope.


Notice the dot of light on the back of the canister in the second picture.

The film canister finder works very well.  I has some movement, but it really easy to align.  It didn’t need to be shimmed, only twisted by a minute amount.  This is actually the second one I made, and I tucked the first one away and am not quite sure where.  The hole is just punched.  It looks like it’s overkill to drill the hole out.

The Solar Funnel Eyepiece


I keep a cap on the end of the EP when not in use.  I’m not sure where/how I’m going to store this, as it’s relatively large.

The View

Note that this looks like you are looking inside something.  But, it’s a flat surface.  You can make out some sunspot activity about halfway out from the center to the left.  I’ve looked through solar scopes before, and this setup shows most of the details that I’ve seen in those scopes, though the scopes can zoom.  The surface of the sun even roils in this view.  One note – don’t try to focus on the edge of the sun, as it’s moving.  Try to pick an interior detail if possible.  Now, some close-ups so you can see the real deal.

This is a big picture–click to thermonucleate!

The dark fleck about an inch up from the bottom is a speck on the back of the screen.  You can easily see three sunspots, and in fact, I could see six.  At one point I thought I saw a brief flare, but it didn’t last very long.  There is also a nice sunspot on the right edge, that you can see better in the next pictures.  I left the fleck out of the picture so that it isn’t confused as solar detail.


Here is a cut of the sunspots that are on the left side of the picture.

One question that might be asked…how do you know the other spots aren’t on the screen.  Well, for one, they move with the sun as it goes across the screen, and second, they can be focused.  Anything on the back side of the screen is always in the same spot, and always in focus.

Many thanks, David, for a very clear and compelling writeup, and for permission to share it here. Now I want to build one more than ever.


The King of Planets courts the Goddess of Love

March 13, 2012

For the next few nights, Jupiter and Venus are going to be as close together in the sky as they’ll get this year. I took this picture this evening from my driveway with my old Nikon Coolpix 45oo, about a 1 second exposure. Jupiter is on the left.

If you have optics, even small ones, you should be able to see the moons of Jupiter and see that Venus is a half-lit D-shape instead of a round ball of light.

I was out for a bit this afternoon and again this evening with the 90mm Sky Watcher Mak. I am learning to live with the finder, and the scope itself continues to impress. This is one of the sharpest bird photos I have ever taken:

The seeing was better tonight than it has been in a long time. I put the little scope on Jupiter and dropped in a 6mm eyepiece for 208x. Jupiter was razor-sharp and zebra-striped with cloud bands. In the steadiest moments, the South Equatorial Belt showed a ragged edge, and a small white storm notched its southern border. It was one of the most mesmerizing things I have ever seen with a small telescope.

As always, I am amazed that a little hunk of metal and glass the size of a 2-liter bottle can do so much. I have really missed having a little Mak around, and I don’t intend to be without one again.


Banner photos, part 1: the little boy with the telescope

March 10, 2012

London with Astroscan

Once when I was a kid Mom and Dad and my brothers and I sat out in lawn chairs until midnight or maybe later to watch a total eclipse of the moon. We only did it once, but it’s always stuck in my mind as Reason #4,769,341 why My Parents Are Awesome (that’s actually a pretty high rank, considering how many museums, zoos, turtles, cats, chickens, model rockets, hikes, skinned knees, dirt clod fights, movies, puzzles, trips to the bookstore, vacations, homeworks, county fairs, kolaches, and giant pans of lasagna went into our upbringing).

The night of February 20, 2008, there was a total eclipse of the moon. It started at 5:45 PM and ended a little after 9:00 PM. We were living in Merced at the time, and I’d only been into amateur astronomy for a few months.

2008-02-20 Eclipse 03

London and I watched the eclipse from the back porch, and Vicki came out a few times to look, too. The “baby red telescope” (a used Edmund Scientifics Astroscan) was my Valentine’s present from Vicki that year. London loves it and at the time he was very possessive about it, but we talked about it and he decided to share. He was just three when these pictures were taken; he’s seven and a half now.

I passed this Astroscan on to a friend, but I got another just for London. They are nearly indestructible scopes. The newest versions from Edmund Scientifics have red-dot sights, but the old ones have a metal peepsight, so there is typically zero user maintenance. That doesn’t sit well with everyone–for one thing, there’s no provision for collimating the mirrors so if they slip out of alignment, you’re basically stuck. Unless you want to disassemble the telescope, that is. For the brave, Gary Seronik posted instructions on how to disassemble, collimate, and reassemble the Astroscan.

2008-02-20 Eclipse end

The tank-like build of the scope is a big selling point. We often take London’s Astroscan when we go camping, because we can always find enough room for it in the car and we don’t worry about it getting banged up. I have read about people who leave their Astroscans in the trunks of their cars on a semipermanent basis so they’re never without a scope, and about Astroscans that have tumbled off tables and tripods and been none the worse for the wear.

One of my favorite observing sessions with the Astroscan was in Yosemite Valley with some ecology students on a field trip. A group of us drove out into the middle of the valley to get out from under the trees, set the Astroscan on the hood of the truck, and spent a couple of hours just cruising the skies. One of the students had never seen Saturn before with his own eyes. It was tiny in the Astroscan–the short focal length limits the magnification–but very sharp, and he stayed hunched over the telescope after everyone else had gone off for some naked-eye stargazing. I will never forget that night; I was so glad I had a scope along and could show people a little of what’s up there (this was about a year before I started doing sidewalk astronomy).

If you want to read up on the Astroscan, the review at dansdata is funny, Tony Darnell has an inspiring writeup here, and Ed Ting’s review is both thorough and charming.

2008-02-20 Eclipse with London 02

If you actually want to buy an Astroscan, you have a choice of paths. The new Astroscan version with the red-dot sight is called the Astroscan Plus, and Edmund Scientifics will sell you one with two eyepieces and a shoulder strap for about $250. For an additional $180, the Astroscan Deluxe package includes a third eyepiece, a sun-projection screen, a tote bag for the scope, and a full-size tripod for getting it up off the ground.

However, you can probably have an Astroscan for a lot less dough if you want. The scope’s basic indestructibility and absence of things for users to fiddle with means that, apart from the switch from the metal peep sight to the red-dot finder, 20-year-old Astroscans are about the same as the ones rolling off the assembly lines today. And the scope has been in production since about the time I was born, so there are a lot of used ones out there. I’ve bought two used Astroscans, the one I passed on and the one London still has, and I found them the same way: put ‘Astroscan Craiglist’ into Google and see what comes up. You might have to do this on a regular basis over the course of a few weeks to find one that is (a) in your area and (b) in your price range, but they do turn up with surprising regularity. You can also find them on eBay sometimes, but usually being sold more dearly. Expect to pay $100-150 for a used Astroscan, although I have seen the occasional one pop up at $75 or even $50 if someone finds one in the back of the closet and just wants it out of the house.

In terms of price and aperture, the Orion StarBlast 4.5 ($180-200)and SkyScanner 100 ($110) are clearly intended to compete with the AstroScan, and if you’re just looking for a reasonably sturdy, portable, 4-inch widefield reflector, either of those would do nicely. But the Astroscan is more maintenance-free (in that it has no provision for user maintenance–whether this is a bug or a feature is up to you); solidly built to the point of near invulnerability; and has a distinctive charm all its own. I suspect that at this point most people don’t end up owning an Astroscan because they wanted a small telescope, but because they wanted an Astroscan specifically. If that’s you, go nuts. It’s an awesome little scope.


Sidewalk astronomy with SkyWatcher Mak 90

March 9, 2012

I took the little SkyWatcher Mak downtown tonight to do some sidewalk astronomy. I haven’t blogged about sidewalk astronomy in a long time because I haven’t done any in a long time. And that’s been bumming me out. I was away from it for too long.

I got started doing sidewalk astronomy back in 2009, as part of the global 100 Hours of Astronomy event during the International Year of Astronomy. It’s a pretty straightforward gig: take a telescope to a public space and give passersby free looks at stuff in the sky. The moon and planets are good targets, because people are familiar with them (not everyone knows what the Pleiades are), they’re naked-eye visible so you can point them out to folks, they punch through city light pollution just fine, and they look great in small telescopes. I know some sidewalk astronomers take big telescopes, and more power to ’em, but I have found that my inclination to go do it is proportional to the size of telescope I have to lug downtown (about five blocks from my house).

For the first long while, my sidewalk scope was my original 90mm Mak, the Orion Apex. It was perfect for the job: compact, lightweight, able to be set up and torn down in about one minute on either end, sharp optics, easy for newbies to focus… Then one night at an astronomy club outreach I reach out in the dark and turned the wrong knob on the mount, and dropped the telescope. On the way down it hit a tripod leg and my foot, but neither absorbed enough energy to keep it from hitting the ground pretty hard. The impact spalled a bit of coating (at least, and possibly some glass underneath it) off the primary mirror. I sold it cheap to a fellow amateur who thought it was salvageable.

My next sidewalk scope was another 90mm Mak, an old orange-tube Celestron C90. I had always wanted one, ever since I saw my  first telescope catalog back at age 12. They are sweet little scopes, build like tanks, and since they focus with a rotating barrel like a camera lens there is not much that can go wrong with them; if the focuser ever gums up you just unscrew the front part of the tube, re-lube the threads, and screw it back together.

It turned out, though, that I liked the idea of the C90 better than the actual thing (this was a far different beast from the modern C90 that is on sale at Amazon and elsewhere). The rotating barrel sounded good in theory, but in practice it was a huge pain to focus the scope while keeping it pointed at an object, especially at moderate to high powers, and especially for people with no experience. I used the C90 for sidewalk astro once or twice and then sold it.

(Aside: one of these days I’ll blog about the joys of buying and selling used telescopes. The bottom line is, scopes hold their value pretty well. If you are judicious and buy used you can usually sell them for what you paid for them, so once you’ve ponied up the initial investment you can essentially try out new [to you] gear for free.)

Then I went through a phase of doing sidewalk astro with bigger scopes: a 5″ f/7 reflector on a homemade mount, a 5″ f/5 reflector (Stubby Fats), and an 80mm f/11 refractor (Shorty Long). These are all fine scopes for showing people stuff in the sky, but not so hot for having to lug five blocks. I needed a dinky scope, something bigger than my 50mm refractor (which is too small for that kind of work) but smaller than my other scopes. Frankly, what I needed was a 90mm Mak, I’d just put myself in the position of not having one.

Until now. Suitably armed with the SkyWatcher Mak, I went forth into the warm spring night, and between 7:35 and 8:45 I showed 48 people the moons of Jupiter. The seeing was godawful, as bad as I have ever seen it. Jupiter was a visibly waving ball of fire, when normally I can see at least half a dozen cloud bands (as shown in the previous post). But the Galilean moons were all visible, strung out in a ragged line to the west of king of planets, and everyone who stopped to look seemed bowled over by the views, so who am I to complain?

I didn’t take the multi-mount that came with the scope, just the little Universal Astronomics DwarfStar alt-az mount that I used to use with the old 90mm Maks (shown in the picture at the top of this post). I left the finder and diagonal on the scope, put it nose down in the included backpack, put spare eyepieces in the side pockets, put all that on my back and carried the folded tripod and mount in one hand. It was great, just like old times.

John Dobson argues that the only measure of a telescope’s value that is worth a damn is the number of people who have looked through it. By that metric, I reckon this little Mak may end up becoming my most valuable scope. I’ll keep you posted!


SkyWatcher Mak 90–more pictures, and using the mount in manual mode

March 4, 2012

More pictures of the SkyWatcher 90mm Backpacker Mak-Cass. Yesterday I took the multi-mount off its tabletop base and put it on my Manfrotto tripod for some digiscoping. I was using it without the power on, as a manually-aimed alt-az mount.

Another of those down-the-tube shots showing the optics. The point of this photo is different, though. Check out the knurled knob on the left that tightens the dovetail. Usually these just have a fat set-screw that goes straight onto the scope’s dovetail bar, and tightening that screw puts a tiny dent or ‘bite’ into the dovetail bar. On this mount, though, the set-screw bypasses the scope’s dovetail bar, and turning the hand knob tightens a broad metal clamp (the silver bit just underneath the hand knob in the above photo) that grips the dovetail bar along its entire length. So the scope is held more securely, and there’s no bite mark on the dovetail bar. Very nifty–I wish more mounts had this.

The big news about using the mount manually is simply that it can be used that way. You don’t want to manually aim the scope once the power is on, or you risk damaging the gears inside the mount, but as long as the power is off you can just grab the tube and point.

A close-up of the back end showing, from left to right, the Astro-Tech dielectric diagonal and 32mm Plossl I was using for birding, the six-screw  mount for the little 8×20 optical finder, and the dovetail clamp and adjacent latitude/altitude scale on the mount.

Getting lined up on a distant bird using the optical finderscope. Imagine that the mount was sitting on its tabletop base and that you were trying to find something high in the sky–eventually there is just no room to get your head behind the eyepiece of the finder. That’s why I strongly prefer RACI–right angle, correct image–finders, which orient the finder eyepiece in the same direction as the telescope eyepiece, so you can look down and in from above.

Waiting for the fall of night.

My two best shots of Jupiter with the little Mak. I could see about half a dozen distinct cloud bands at the eyepiece, and for once the photos bear that out. As usual, however, I could still see more detail at the eyepiece than the camera captured. The views are not as good as through the Apex 127–compare to the Jupiter photo here–but they’re not that far behind.

The waxing gibbous moon, again with the little Mak. This is probably the sharpest moon photo I’ve ever gotten with a 90mm Mak. This SkyWatcher scope is at least as good, optically, as the Orion Apex 90 I used to have. I don’t know yet if it’s as good as the Celestron C90, which has gotten stupid-good reviews, but I don’t think it will disappoint anyone. Last night the sky was still enough that I could run it up to 200x and the view was still razor-sharp. That’s 57x per inch of aperture, compared to the rough rule of thumb of 50x/inch in a good scope, so this little scope is punching above its weight. I haven’t tried to max out the magnification to see where it breaks down, but I think it will probably be quite a bit higher.

The fact that the meniscus is merely coated instead of multi-coated has not impaired the scope’s performance as far as I can tell. Possibly the few percent difference in light transmission will be noticeable when one can switch back and forth between this scope and one with a multi-coated meniscus; it is certainly not noticeable when using the scope on its own.

I still haven’t had time to try out the tracking function on the mount, but this afternoon I did put batteries in and slewed it around and didn’t have any problems. I’ll report back when I’ve had it out tracking under the stars.


The SkyWatcher 90 Backpacker on the moon and some birds

March 2, 2012

Fate smiled on me yesterday and early this morning, and I was able to get some pictures with the SkyWatcher 90 mm Backpacker. If you’re impatient you can scroll to the bottom of the post for the photos.

I should stop here and say that I ultimately intend to test the whole kit–scope, mount, and accessories–as a system, because whether you use it as-is or mix-and-match components, it is sold as a system and is at least theoretically supposed to function as one. However, between teaching, taking a statistics class, and wrangling ostriches, I just haven’t had time to mess with the mount. My primary concern has been to assess the optical quality of the scope–and now I actually have some information.

I got in a brief observing session between responsibilities yesterday afternoon. I was plinking around the yard, looking at birds. For these observations I started out using the included 90-degree prism diagonal and 25mm Plossl eyepiece. I first looked at a couple of obvious birds silhouetted against the sky in treetops, and they looked fine. Then I went after one hidden in the leaves and branches of one of my neighbor’s trees, and in those dimmer conditions I noticed something unnerving: the eyepiece view was very soft and didn’t snap to focus, as if I was observing with a very short focal ratio scope like an Astroscan. Also, there was some ghosting of the image in the eyepiece, and the edge of the image was poorly defined. In short, it was very, very different from the crisp, sharp, detailed images that Maks are renowned for, and not in a good way. I was just having a “Hey, what the–!” moment when I remembered where I had seen these kinds of problems before: in scopes using cheap prism diagonals instead of mirrors.

Without moving the scope, I went to the garage and pulled the Astro-Tech dielectric diagonal off my Apex 127, and swapped that out for the prism diagonal. I held my breath as I put my eye back to the eyepiece–were the problems all in the diagonal, or had I gotten a lemon of a scope?

Sweet relief–even in the dim light amongst the leaves and branches, the view was razor-sharp and contrasty. It was like someone had run a very good image-sharpening algorithm on the eyepiece view. Suddenly details that were invisible before were popping out all over the place. Leaves that had been too fuzzy to invite close inspection were etched with delicate networks of veins. The whole view just looked more real.

I decided then that I would try to find out just how good or bad the prism diagonal is, and under what conditions.

After that quick peek I didn’t get another chance to use the scope until about 10:00 last night. The first quarter moon was still fairly high in the west, but the seeing was not good. The air just roiled over the moon, and every star I looked at scintillated with fast-moving rays of light. Not good conditions for testing a new telescope, because it’s hard to push the magnification up and tell if the results you’re getting are because of the scope, the seeing, or both. But I went ahead and put the scope through it’s paces anyway. The thing about seeing is that from time to time it does settle down a bit, at least momentarily, and in those instants the amount of additional detail that is visible is sometimes shocking. So the longer you look and the more patiently you observe, the more likely you are to catch those rare moments of steadier air and see something really remarkable.

For eyepieces I used a 32mm Sirius Plossl from Orion and the 12.5mm and 6.3mm SkyWatcher Plossls that came with the scope. I took all of the pictures in this post afocally with a Nikon Coolpix 4500 hand-held to the 32mm Plossl, and with the camera optically zoomed enough to eliminate any vignetting.

The moon looked surprisingly good with the Astro-Tech diagonal in place. It was fairly swimming in the turbulent air, as if being viewed under a thin stream of moving water. But if I focused on a particular crater or feature for the space of a minute or two I would catch a patch of calmer air and see perhaps double the detail in those brief glimpses. Small craters that were otherwise just spots would pop into focus with dark rims and bright floors. The 12.5mm eyepiece had tighter eye relief than I am used to in that focal length; I have long-ish eyelashes and they were occasionally brushing the eye lens, something I don’t remember ever happening with the 12mm SkyWatcher Plossl that I got with Shorty Long, my 80mm f/11 achromat. That 12mm looks identical to the Orion Sirius line, whereas the eyepieces that came with the Backpacker have smooth silver barrels and no rubber eyecups, so even though they are both branded SkyWatcher they might have somewhat different guts. Also, I’ll have to look more closely the next time I’m out, but the 12mm felt like it had a narrower apparent field of view than the 32mm, which shouldn’t be possible if they are both Plossls, which typically yield a 52-degree apparent field. Could be that the short eye relief was playing tricks on my perceptions. Anyway, with the 12.5mm EP in the scope was working at 100x and I was still seeing plenty of few detail in the still moments.

I put the 6.3mm EP in just for the heck of it. I wasn’t expecting much, both because of the punk seeing and because that magnification–200x–ought to be pushing on the edge of what this scope can do. A commonly used rule of thumb is that a good scope should be able to handle 50x per inch of aperture. At 3.5 inches, any of these 90mm Maks ought to be good up to at least 175x. But I have to point out that the 50x/inch “rule” is often broken and not only by premium scopes. David DeLano has had his 114mm reflector up to 400x (89x per inch), and the other night I took my Apex 127 to 514x (103x) to split a close double star that was not split at 257x. I’ll just note that those are both relatively long focal ratio scopes, about f/8 for David’s reflector and f/12 for the Apex, and maybe that has something to do with it; such gently-tapering light cones are certainly easier on eyepieces and so on. Anyway, at 200x with the 6.3mm EP I was still getting glimpses of considerable detail. I can’t say for certain because of the lousy seeing, but I think this scope can handle 200x. I hope I get a still night soon to test that.

Okay, so far so good with the Astro-Tech diagonal. I swapped it out for the stock prism diagonal and went back to the 32mm Plossl. YUCK! I almost could not focus my eye on the moon, because there was a moon-sized ghost image floating around in the field of view that looked like it was probably some kind of reflection of the primary mirror or maybe even the corrector. It was a big white donut with a dark hole in the middle, anyway. I’ll stress that this ghost image or whatever it was was not there with the Astro-Tech diagonal. I have never seen anything quite like it before, and given the controlled conditions of time, place, observer, scope, and eyepiece, I feel confident blaming the prism diagonal.

I tried the two other eyepieces. The ghost didn’t show up in either of them. The 12.5mm was merely okay, producing a slightly softer view in the prism diagonal than in the Astro-Tech. The 6.3mm was very noticeably softer; this time going from 100x to 200x looked and felt like empty magnification.

I also looked at Belelgeuse and Mars with all combinations of diagonals and eyepieces. Betelgeuse was sparkling in the Astro-Tech diagonal, but at least the scintillating rays of light were sharp. In the prism diagonal it was a fuzzy mess. Betelgeuse was down near the horizon, though, and Mars was very high, so I hoped to see at least some detail on good old Barsoom.

Mars really required the 12.5mm EP; at 39x it was a bright orange BB, too small to see detail on, and at 200x it was a big orange smudge. At 100x with the prism diagonal I could only suspect the polar cap, and that might have been because I knew it was there to be seen. I had started that run with the Astro-Tech, and in steadier moments the polar cap was a well-defined white patch with a hair-fine black border. In brief flashes I also saw dark markings on the face of the planet’s disk. So despite the lousy seeing, the little scope lived up to the Maksutov reputation as a fine planetary instrument.

I did see some off-axis glare from Betelgeuse and Mars, but only in the 32mm Plossl. I am going to do some more testing to see if that is a scope issue or, as I suspect, an eyepiece issue. Also, getting the scope on target using the 8×20 straight-through finder was not difficult but it was uncomfortable, and usually required me to move my chair, squat behind the scope, and go back and forth between sighting down the tube and squinting through the finder. It’s doable, it’s just not fun, and something like a 6×30 RACI should be a high-priority upgrade if you get one of these.

This morning before work I got some photos of neighborhood birds, using both the Astro-Tech dielectric diagonal and the prism diagonal that came with the scope. Be aware that that both my camera and my photographic method are primitive. The camera is a 4-megapixel job more than a decade old now, and while its rotating barrel design is convenient for digiscoping, it just can’t keep up with the better modern cameras. Also, hand-holding the camera to the eyepiece means that I’m usually the most mobile link in the system, so any fuzz or blurring in the photos is possibly caused by my minuscule shakes rather than by the optics. To try to eliminate that factor as best I could, I took several exposures of each target and picked the sharpest from each set for the comparison images. In all of the comparisons between diagonals, the photo through the prism is on the left, and the dielectric photo is on the right. Other than having been put into the same image for comparative purposes, the photos are completely unprocessed: no sharpening, no levels or curves, no rotation, and I didn’t even flip the photos through the star diagonal, which are reversed left-to-right. Click each image for the original, full-resolution version.

The moon last night. The view through the dielectric diagonal was markedly sharper and more contrasty, and these unprocessed photos, taken just minutes apart, bear that out. The full-resolution dielectric photo shows a very thin line of purple chromatic aberration around the limb of the moon, but I couldn’t see it at the eyepiece despite being on the lookout for it.

This fellow was sitting a tree that I have paced out at about 70 yards from my driveway. Again, the dielectric photo (right) has better contrast, and look at the difference in the color of the background sky. This is the same bird and I took the photos about 2 minutes apart.

This dove was quite a bit farther way. I haven’t paced it out, but this powerline must be well over 100 yards from my driveway. Notice the scale of the bird in the photos and the pronounced drop-off in detail compared to the little songbird above. Detail is probably a wash here, but the dielectric photo has better contrast and again the background sky is more blue.

One more point to make is that I hardly ever post raw images. Almost every photo can benefit from a little processing with Unsharp Mask and Curves (I use GIMP, which is free–see details on what I do to each photo in this post). Here are the best dielectric photos of the moon and the songbird, with the unprocessed photo on the left and the lightly processed version on the right (this time I did rotate the moon and flip it to its correct side).

So, what did I learn from all of this? The SkyWatcher 90 Backpacker is a decent little scope. I couldn’t see any optical problems, and I was impressed to see details on Mars at 100x with the included Plossl and the Astro-Tech diagonal. Views of birds are as good as those I used to get with my Orion Apex 90. But the supplied diagonal is not good, and really limits the views the telescope is capable of providing. If you get one, replacing the diagonal with even an inexpensive mirror diagonal should be a top priority. Let me put in a plug here for the Astro-Tech dielectric diagonal. It consistently throws up a great image–it’s the diagonal I used when taking the Apex 127 to 514x for that double star split–but at $69.95 for the 1.25″ version it is no more expensive than some ‘entry-level’ mirror diagonals.

The supplied prism diagonal does have one potential use: if you have an old binocular laying around, you can disassemble it and use one of the objective lenses to make a proper finderscope, and if you include the diagonal it could even be a RACI. Mounting a bigger homemade finder to the scope will take some ingenuity, but I figure anyone who likes to tinker enough to build a finder in the first place can be trusted to come up with a mount as well.

So I now feel confident enough to recommend the scope, at least, although the mount is still a question mark and the diagonal and finder are troublesome (as expected). I don’t know how the scope performs compared to the Celestron C90, which is also on sale, because I haven’t had the chance to test them side-by-side. But with a little luck I may get that chance soon.

Hopefully this weekend I’ll have time to get the mount up and running. Stay tuned.