Archive for the ‘SkyScanner 100’ Category

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Why and how to make a sub-aperture mask for a refractor

February 11, 2017

60mm-aperture-mask-6-comet-edition-close-up

Here’s the Bresser Messier AR102S Comet Edition with a homemade aperture mask. I just converted the scope from a 102mm f/4.5 to a 60mm f/7.7.

“WAT!? You took a refractor, the most aperture-challenged of the three basic telescope designs, and made it even smaller?”

Yup. For several reasons.

The first and most obvious is to control chromatic aberration (CA), also known as false color. Despite the name ‘achromat’, which literally means ‘no color’, doublet refractors without extra-low dispersion (ED) glass do show some false color, because their lenses do not bring all of the colors of light to the same focus point (they’re still a LOT better than scopes with a singlet objective lens, like those used by Galileo). For dim objects like galaxies, nebulae, and most field stars, the effect is not noticeable, even in large and optically fast scopes like the AR102S Comet Edition (nickname needed). But bright objects like the moon, planets, and first magnitude stars will be surrounded by purplish halos, and may have yellowish margins. In effect, the purple and yellow-orange parts of the spectrum are forming out-of-focus images that are superimposed on the main in-focus image.

The problem is that CA gets bad fast as refractors get bigger. There are a couple of standards that are commonly used to describe the focal ratio necessary to minimize CA to acceptable levels, the Conrady standard and the Sidgwick standard. By the Conrady standard, the focal ratio must be 5 times the aperture in inches; by the less stringent Sidgwick standard, 3 times the aperture in inches is good enough. Note that the standards describe focal ratios, not focal lengths, so they go up fast with increasing aperture. Here are some apertures, focal ratios, and focal lengths required to meet the Sidgwick standard:

  • 50mm (2″) : f/6 : 300mm
  • 76mm (3″) : f/9 : 684mm
  • 102mm (4″) : f/12 : 1224mm
  • 127mm (5″) : f/15 : 1905mm
  • 152mm (6″) : f/18 : 2736mm

This, along with mounting considerations, explains why reflectors and catadioptric scopes are progressively more common past 4″ in aperture. A 6″, f/8 Newtonian will be free of false color (as are all reflectors) and has such a gently converging light cone that it is easy to collimate and to focus – it’s easy for such scopes to achieve ‘planet-killer’ status if the mirror is good. A 6″, f/8 achromat will be a beast to mount and it will show lurid false color on bright objects.

But people still make, buy, and use such scopes! Why? Horses for courses: big, fast achromats can be superb deep-sky scopes, where chromatic aberration is typically not a problem. With the fixed sizes of standard eyepieces, achieving wide true fields requires short focal lengths (not just short focal ratios), and bright images require aperture, which drives the development of large but optically fast scopes like the AR102S Comet Edition. At f/4.5, it is well into ghastly CA territory on bright targets. The other night I stayed up late to catch Jupiter, and in the AR102S the planet wouldn’t even come to a clean focus. It was just a bright ball of light inside a sea of purple. I switched over to London’s 60mm f/11 Meade refractor and Jupiter snapped into a sharp and essentially color-free focus. There was a moon emerging from behind the limb of planet, already one moon-diameter out into black space, that was completely invisible in the CA-smudged view of the AR102S.

I’m okay with that – as I noted in a previous post, observing bright solar system targets with the AR102S is deliberate misuse of the scope. When I want good planetary views, I have a 5″ Mak and a 10″ Dob that can both be pushed to 500x (assuming the atmosphere is steady enough). But their max fields of view are pathetic compared to the AR102S – about 1.1 degrees for the Mak, and a shade over 2 degrees for the Dob, versus 3.6 degrees for the refractor, which is enough to take in all of Orion’s sword at once, with space left over on either side.

Still, I’m not going to take all of my scopes out with me every time I go observing, and chances are good that at some point I’ll want to look at something bright even if my main goal for the evening was low-power sweeping with the AR102S. Under those circumstances, it’s easier to have an aperture mask shoved in my eyepiece case than to pack a second scope. Hence this project and this post.

But I’m getting ahead of myself. There are other reasons to stop down a scope besides reducing CA:

  • To reduce glare from bright objects. Mostly applies to the moon when it’s full or very gibbous.
  • To give a more aesthetically pleasing image when the seeing is bad. Opinions differ on this point. Some folks prefer to look through a larger aperture despite the increased susceptibility to bad seeing, on the grounds that in the moments when the atmosphere does settle down a bit, you’ll see more detail. I suppose it depends on whether one is in exploration mode or aesthetic observation mode.
  • To make it easier to focus. F/4.5 is a steep light cone, and it’s easy to overshoot the point of best focus. Stopping down the scope makes a shallower light cone, so it’s easier to watch the image transition from out of focus, to near focus, to in focus. I’m going to test this method of finding best focus on some close double stars.

I had done some calculations in advance to figure out what sizes of aperture masks I’d want to try out. Given that the AR102S has a fixed focal length of 459mm, here are the focal ratios at full aperture and at 10mm decrements:

  • 102mm gives 459/102 = f/4.5
  • 90mm gives 459/90 = f/5.1
  • 80mm gives 459/80 = f/5.7
  • 70mm gives 459/70 = f/6.5
  • 60mm gives 459/60 = f/7.7
  • 50mm gives 459/50 = f/9.2
  • 40mm gives 459/40 = f/11.5

3-inch-sub-aperture-mask

I didn’t want to trade away too much resolving power, so I tested the scope on the moon using cardboard masks of 76mm and 60mm, made from the light cardboard spacers from a box of wet cat food. The 76mm is shown above. Perhaps unsurprisingly, at this aperture and focal ratio (f/6) the view was still unappealingly soft. But 60mm looked good, with minimal CA. This makes sense – the working focal ratio of f/7.7 is a healthy step beyond the f/7.2 that the Sidgwick standard suggests for a 60mm aperture. Going any smaller would be trading away valuable resolution, without significantly improving the image.

60mm-aperture-mask-1-gallon-jar

The light cardboard aperture masks were fast and easy to make, but they weren’t very sturdy. To make a more permanent mask, I needed plastic, heavier cardboard, or foam-core board. So I unscrewed the dewshield from the scope and walked down to the dollar store, where I looked for food packages and storage containers that might fit. Finally on the last aisle I found this 1-gallon plastic jar. The lid slip-fit over the dewshield with just a bit of extra room, which I knew I could shim out with some sticky-back felt.

60mm-aperture-mask-2-marking

I wanted to make sure the lid would fit before I did the hard work of cutting, so I put the felt on first. This was very familiar – it seems like every other scope I get has a loose dust cover that has to be shimmed to fit correctly. I’ve been slowly chipping away at the same package of sticky-back felt since 2010. I didn’t have a compass handy, so I used a small paper ruler to make a ring of marks around concentric 60mm circle inside the lid. Then found a lid to a jar of vitamins that was exactly 60mm in diameter and used that to trace the circle neatly.

60mm-aperture-mask-3-completed-mask

I was going to cut out the aperture using hobby knife, but the plastic was too tough. So I moved up to a box knife, and then a linoleum knife. Then I said heck with it and got the Dremel. The hole I cut wasn’t perfectly circular and had rough edges to boot, so I wrapped some sandpaper around a pill bottle to make a tool for rounding out the aperture.

60mm-aperture-mask-4-comet-edition-before

Here’s the scope before…

60mm-aperture-mask-5-comet-edition-after

…and after.

Even with the aperture mask, the AR102S is not a champion scope on solar system targets. The C80ED blows it away, which makes sense – it has a 33% resolution advantage over the stopped-down AR102S, and frankly just better glass. But at least the view now is clean and not appallingly degraded. A dramatic way to see the difference is to get a good tight focus on the moon with the mask on, then quickly take it off without removing one’s eye from the eyepiece, and watch the view get a lot brighter and a lot softer at the same time.

I have a few more things I want to do. The 60mm aperture mask fits over the end of the scope so securely that it could work as a dust cover, if only I can find or make something to plug the central hole. Also, I think I am going to play with making aperture masks in other sizes, just to see what happens.

And finally, I have another 4″ scope that will be fun to make an aperture mask for. But that will be a subject for another post.
skyscanner-aperture-mask-test-fit-jar-lid

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Hacking the SkyScanner 100: six easy pieces

February 7, 2017

skyscanner-100-before-hacking

Remember this thing? It’s a lovely little scope, but I got tired of crouching over it. And it’s made out of tractable materials – rolled steel and particle board, mostly – and costs next to nothing as these things go ($100 as of this writing), so it was basically crying out for customization. I made six fixes – two on the base, two on the outside of the tube, and two on the inside of the tube. They’re all cheap, fast, and easy, hence the title of the post (with apologies to Richard Feynman!).

skyscanner-hacks-1-eyepiece-rack-and-handle

My first two mods were to the base. (1) I had a leftover eyepiece rack, which I screwed to the base in the only place and at the only angle that it would fit. It works great. My very first scope, an Orion XT6, came with an eyepiece rack like this (which has since been dropped from the base model XT6), as did my XT10, and I’ve always found them to be very convenient. It took me a long time to realize that an eyepiece rack didn’t have to be horizontal to work, especially if the eyepieces are always capped so they can’t fall out.

(2) The second mod is the wire handle on the top of the base, which I scavenged from an earthquake stabilization kit for furniture. It’s just a small woven steel wire with an eyelet at either end which is screwed into the particle board that makes up the base. When I put it on, I thought I’d cut a piece of aquarium tube to slide over it as a cushion. I still might do that at some point, but so far I haven’t needed to. The whole scope and mount only weighs 6 lbs, maybe 7 with a full eyepiece rack, and I’m never carrying the scope that far. Basically from the garage to the driveway, or from the car to a picnic table. So the wire handle has not had the opportunity to get uncomfortable yet. This was the simplest mod but may be the one that has made the most difference in terms of overall convenience. Orion should just build ’em this way, even if it bumped up the price by five bucks.

The piece of tape on the tube is covering the holes intended for mounting the dot finder. I never used it, and now the holes are in an inconvenient place. I’ll come up with a more permanent and better-looking solution than the tape, but at least it keeps dust out of the tube for now.

skyscanner-hacks-2-focuser-position-and-laser-trough

This photo shows the two mods to the outside of the tube. (3) Originally the focuser pointed straight up, with the focus knobs on the opposite side of the base arm. I wanted the focuser to face up at a comfortable angle, so I wouldn’t have to lean so far over the scope while using it. And I wanted the knobs on the same side as the base arm, so the eyepiece rack would face the user. Achieving both of those goals meant moving the scope’s dovetail bar about 135 degrees around the tube. To do that, I had to drill new holes in the tube. I used a paper wrap to get the new holes lined up with the old ones and with each other, made pilot dents using a thumbtack, then drilled them out with a cordless electric drill. It’s not a good idea to have metal filings flying around precision optics, so I removed both mirrors before drilling the holes. It’s fun to take a telescope all the way apart and put it back together, especially if it works better after you’ve done so. Everyone should try it.

(4) Once I had the dovetail moved over to the new holes, I had a couple of perfectly good holes in the tube in a convenient place, and at a convenient angle from the dovetail and the focuser. So I built a laser trough to go there. It’s an idea I got from Ken Crowder, a former PVAA member. Back in 2010 on one of my first trips to the Salton Sea, Ken had his 8-inch SCT set up with a video camera for taking integrated shots of deep sky objects. To help get on target, he had wooden bracket pretty much like the one you see above, into which he would lay his laser pointer. Lots of companies make special rings for adapting handheld laser pointers into telescope finders. But like me, Ken wanted to be able to do other stuff with his laser at a moment’s notice, like trace out constellations for newcomers, or point out especially nice things in the sky without moving his telescope. The wooden bracket lets you drop in the laser and get on target quickly, and then lift it out and use it for other things.

To fine-tune the aim, Ken would shim his with little scraps of wood and paper, and I intend to do the same if necessary. But with the SkyScanner’s 400mm focal length, a 32mm Plossl yields 12.5x and 4-degree true field of view, and even a 25mm gives 16x and a 3-degree field, so even without shimming the laser is usually good enough.

skyscanner-hacks-3-laser-trough-close-up

Here’s a close-up of the laser trough. I built it out of wood scraps and glue. The hardware store didn’t have hex-cap metric screws in the size I needed so I got machine screws and washers. I used a spade bit to cut little indentations for the hardware. The two square stringers on the bottom are to help keep the whole rig aligned with the long axis of the tube.

skyscanner-hacks-4-primary-center-spot-and-secondary-bolts

Finally, the two inside-the-tube mods. (5) I center-spotted the primary to aid in collimation. The best thing to use for this is a notebook reinforcing ring. I have a whole package of those somewhere, but I can’t find it. But I did find a package of the little round stickers of the kind you use to make price tags at garage sales, and made it into a ring with a handheld hole punch. It works great. I have doubts about its longevity, but if and when it falls off, I’ll just make another. It seriously takes less than five minutes. Most mass-produced reflectors these days ship with their primary mirrors already center-spotted, and it really helps with collimation.

(6) As explained in the last post (link), I swapped the stock Allen bolts for secondary collimation with standard hex-cap bolts that I can turn by hand and lightly tighten with a small pair of pliers.

skyscanner-hacks-5-all-ready-to-go

So how does the reborn SkyScanner work? Pretty darned well! It was already an extremely convenient and easy-to-use scope, and now it’s even moreso.

I’m not done hacking on it. As shipped, the primary mirror can’t be collimated. I read on CN about lengthening the bolt holes in the OTA that the mirror cell is screwed into, so that the mirror cell can be tilted to achieve primary collimation. I tried this and didn’t like the results. It’s very hard for me to get the mirror cell mounting bolts tightened down enough to keep the mirror cell from shifting. Especially because it’s natural to grab the back of the scope to help aim it, and in doing so I almost always shift the mirror cell relative to the OTA and subtly throw off collimation. Or not subtly – at f/4, every last arc-second of collimation matters. So I’m going to build a fully-collimatable mirror cell.

And I’m going to figure out a better way to cover those holes in the tube for the finder. And flock the inside of the tube, and make a long dewshield to keep stray light from hitting the secondary and the focuser drawtube. And probably do some other stuff I haven’t thought of yet. I’m basically going to treat this scope as a testbed for every hack I can think of. Should keep me busy for a while.

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Upgrading secondary collimation bolts on a reflector

February 5, 2017

dscn1615

Here’s a fast, cheap, and easy hack that I do to every reflector that passes through my hands. I hate messing around with hex wrenches while collimating my reflectors, so I replace the Allen bolts with standard hex-cap bolts that can be turned by hand and lightly tightened with a socket wrench or pliers.

I’ve done the mod to all three of the StarBlast 4.5s that the PVAA has placed with the Claremont Public Library – which I am responsible for servicing every couple of months – as well as to my XT10, my SkyScanner 100, London’s XT4.5, and the 5″ f/5 SkyWatcher Newt I had a few years ago. You’ll notice that so far, all of the scopes I’ve done this to have been Synta-made and Orion or SkyWatcher branded. All of the smaller ones have taken identical hardware, but I did the XT10 so long ago I don’t remember – I think it took longer and possibly larger-diameter bolts, but I could be talking crazy.

If this is something you’re interested in doing, you need to take two measurements, make a run to the hardware store, and do about five minutes of work when you get back home. Or you can get a set of Bob’s Knobs, which are much nicer and designed for no-tool use. But making your own with hex-cap bolts costs less than five bucks and gives passable results, and doesn’t stop you from picking up Bob’s Knobs later if you like.

The first thing you want to know, that you can only find out from your assembled spider/secondary mirror mount, is the length of bolt that you’ll need. The secondary holder has two parts, the hub that the spider attaches to, and the 45-degree-angled mirror holder that is usually attached to the back of the secondary mirror itself with double-sided tape. The collimation bolts engage with threads in the hub, and bear against the flat back surface of the mirror holder. The Allen bolts that the scopes ship with are much shorter than the distance from the mirror holder to the front of the hub. So collimation requires sticking a hex wrench down the hole blindly and fumbling a bit to get it seated in the socket (at least for me – if that doesn’t bother you, this post will probably not be of much use).

secondary-mirror-diagram

If you’re going to replace those little shorty Allen bolts with regular bolts, you need to know the distance from the mirror holder to the front of the hub – it’s the dimension between the dotted lines in this diagram, labeled “min. length for bolts”. Your replacement bolts need to have shafts at least this long, or their caps are going to run into the hub before they engage with the mirror holder. It doesn’t really matter how much longer they are, as long as it’s not ridiculous – you don’t want them sticking so far out of the front of the scope that they’ll catch on things or scatter light into the tube.

The second thing you need to know is the type of collimation bolt your scope has – its diameter and thread pitch. If you don’t know that, and you probably won’t the first time out, just back one (and only one!) of your Allen bolts all the way out, and take it with you to the hardware store.

metric-bolt-gauge

At the hardware store you’ll find a bolt gauge like this one. Actually you’ll probably find two, one for English hardware and one for metric. If you have a scope made in China, it probably uses metric hardware, so start there.

testing-original-bolt

Here’s a close-up of me testing one of the collimation bolts from the SkyScanner in the metric bolt gauge. As you can see, it fit the 4mm socket.

replacement-bolt-bag

I already knew from measuring the scope’s secondary that I needed bolts longer than 20mm. And here’s my part: a 4mm x 25mm (diameter x length) bolt, part #81494 at Orchard Supply and Hardware. I bought six – three for my SkyScanner 100, and three for London’s XT4.5, which I hadn’t done yet.

testing-replacement-bolt

My motto is “trust but verify”, especially before buying hardware. If unbagging a part to test it in the store makes you queasy, you can just push the end of one bolt through the bag, enough to try it on the bolt gauge. This won’t destroy the packaging should you need to put it back – buy it or leave it, you can poke the bolt back into the package and only leave a tiny hole (in this case, 4mm!).

original-allen-bolts

Here are the old bolts ready to go into the bag, which has all of the original Allen bolts from half a dozen reflectors now. I don’t know why I save them. I ‘m kind of an astro-hoarder. If anyone out there wants these, let me know and I’ll send them to you gratis.

Anyway, so far, so good. You get home, back out the Allen bolts, and replace them with the hex-cap bolts. Now, this is important: for your sanity, replace the bolts one at a time. If you screw all of the original Allen bolts out before putting in any of the replacements, your secondary is going to be flopping around uselessly. It may well rotate in place and end up not even facing the focuser drawtube. Take it from an idiot who has done this! But if you replace the bolts one at a time and get all of the replacements finger-tight, the mirror will maintain its radial orientation and may even stay in pretty good collimation through the procedure, although of course you’ll want to recheck and touch up the collimation when you’re finished.

There are loads of good sources on Newtonian collimation online so I’m not going to reinvent that particular wheel. I’ll just add a couple of tips that have made my life a lot easier. The first is to try to balance the push and pull on the three collimation bolts. In other words, if you want to screw in one bolt, back off another one first. If you only ever collimate by screwing in, you’re going to either run out of travel, jack up your mirror holder, or force it farther down the tube, depending on what the deal is with the mounting bolt (some are spring-loaded, some aren’t). When I sit down to collimate the secondary, I quickly go around to each bolt and turn it both ways, backing out first and then screwing in, to get a sense for what each bolt does.

The second tip is specific to these replacement hex-cap bolts on the Orion/Synta scopes that I own and service. Once I get the secondary collimation where I want it by tightening the bolts with my fingers, I go back around and give each one a small additional twist, maybe a sixth of a turn, with the little pliers I keep in my eyepiece box (see here). If I do this evenly to all three bolts, it doesn’t affect the collimation, and the extra bit of tightness helps the scope stay in collimation longer. That might no be needed or even helpful depending on how the mounting bolt engages the mirror holder. Play around with it and see what works for you.

Replacing these bolts was just one of half a dozen hacks I made to the SkyScanner 100. The rest will be covered in another post very soon. Until then, clear skies!

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SkyScanning in Utah – and Claremont

July 25, 2016
SkyScanner in classroom

Everyone should have one of these.

I’ve been interested in Orion’s SkyScanner 100 tabletop Dob ever since 2012, when I got to look through the SkyScanners owned by Terry Nakazono and Doug Rennie. In particular, the evening I spent stargazing with Doug up in Oregon that October is in my short list of all-time favorite observing sessions. See that observing report here, and be sure to check out Terry’s guest post on the SkyScanner 100 here.

After spending literally years contemplating the purchase, what finally tipped me into SkyScanner ownership was my own forgetfulness. On July 3 I was driving to Utah to spend 10 days hunting dinosaurs with friends and colleagues. I knew I’d want some dark-sky time so I packed my C80ED, eyepiece case, sky atlas, and binoculars. About the time I hit Barstow – just too far to turn around and go back – I realized that I’d forgotten to pack a mount and tripod. So my choices were to roll with binos only, or come up with Plan B on the fly.

The number of dedicated telescope stores on the direct route between Barstow and Moab continues to hover near zero. However, I was already planning to pass through Flagstaff, which has the Lowell Observatory, which has a gift shop. I called ahead: did they have any telescopes in stock? Why, yes, the Orion XT8 and SkyScanner 100, and both were 10% off as part of a holiday weekend promo. Not long after, I had a SkyScanner in the back seat of the car and a song in my heart.

Matt with SkyScanner 100 at July 2016 PVAA meeting

Demonstrating how the SkyScanner can ride on any tripod with a 1/4 or 3/8 bolt.

I spent that first night in Bluff, Utah, after having driven through Monument Valley, which I’d never visited before. Bluff is truly remote – the nearest towns with more than 5000 people are Moab (5046), 100 miles north, and Kayenta, Arizona (5189), 68 miles southwest. So the skies are inky dark. I rolled in pretty late and I really needed to get some rack, but there was zero chance that I was going to pass up first light for the SkyScanner under those jet-black southern Utah skies. I drove about five miles outside of town and pulled over on a dirt road.

The sky was just incredible, even better than out on Santa Cruz Island back in June. Again, the Milky Way looked like an astrophoto and the Messiers in Scorpio, Scutum, and Sagittarius were almost all naked-eye visible (minus a few of the minor globs). I did look at a handful of things with the SkyScanner, and they all looked fine, but honestly I spent more time with my 10×42 binos and even more time than that just staring around with my naked eyes. In skies like that, a telescope can almost be a distraction.

Still, I’m glad I got that first light session in on the evening of the 3rd, because opportunities would be thin for a while. I did set up the scope on the 4th of July, on the trunk of the car in the driveway of my friends’ place in Moab, and we looked at a few things, but everyone was pretty pooped after a day of hunting dinosaurs and partying so we didn’t push very late. And after that, the sky was at least partly cloudy for most of a week.

Finally on the evening of July 10th we got nice, clear skies. I drove out southeast of Moab on the La Sal Loop Road with a couple of new friends and we spent a very pleasant couple of hours rocking through the best and brightest. The SkyScanner performed like a champ.

Howard Karl and Matt at July 2016 PVAA meeting

Karl Rijkse (center) shows his heirloom German binoculars to Howard Maculsay (left) and me.

I’ve only had it out a couple of times since betting back to Claremont, both times for quick peeks. As a grab-n-go scope it is, as far as I’m concerned, unparalleled. With an assembled weight of just over 6 lbs, it is the definition of a one-hander. The tabletop tripod works great, very smooth, and the rubber feet provide a good grip even on the precarious edge of a sloping car hood. And it goes on my Manfrotto tripod (3.5 lbs) for a 10-pound setup that’s perfect for a long session seated or standing.

As you can see from the photos (kindly provided by Terry Nakazono), I took the SkyScanner to last Friday night’s meeting of the Pomona Valley Amateur Astronomers, where it drew a lot of interest. I was going to set up the scope outside after the meeting so we could all have a look at Saturn, but the night sky was almost completely blocked out by smoke from the wildfires and the air quality was terrible, so we packed it in. I think I’ll get in the habit of taking the scope to meetings so we can do a little observing after – it’s always seemed to me that an astronomy club should have at least one working scope at each meeting.

Here’s my number one thought regarding the SkyScanner 100: how extremely stupid of me not to have gotten one sooner. If you’re interested in this scope and you’re on the fence, just do it. Heck, if you’re shopping for a big scope and you’re not sure what you want, get a SkyScanner to keep you busy in the meantime. It’s an insane amount of scope – and mount – for a little over a hundred bucks.

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Observing Report: SkyScanning in Oregon

October 2, 2012

I was up in Oregon last week to visit my university’s second campus in Lebanon. It was a kill-many-birds-with-one-stone type trip: in addition to day-job work in Lebanon on the weekdays, I got in a productive meeting about a joint project with a paleontological colleague who lives nearby, and–the point of this post–last Wednesday night I got to go stargazing with frequent commenter Doug Rennie.

Doug lives up by Portland and I was staying in Albany, so we needed someplace in between with reasonably dark skies. We settled on Baskett Slough Wildlife Refuge, just north of Dallas, OR. We met in Dallas for dinner and then drove out to the slough.

I had along a new-ish pair of Nikon Action 10×50 binoculars that I picked up this summer and haven’t used much. Doug brought his Celestron SkyMaster 15x70s–the same model I have and love–and his Orion SkyScanner 100 tabletop telescope.

Neither of us really knew what to expect in terms of sky quality. The waxing gibbous moon was only three days shy of full, and I was seriously concerned that we’d get “mooned out” and not be able to observe anything in the deep sky.

This brings up the interesting question of how much moonlight it takes to significantly degrade the night sky. I’ll write a full post about it someday, but for now it is enough to note that the brightness of the moon increases exponentially on the run up to opposition (full moon), and decreases exponentially after full moon. For explanations of why that is, check out this graph and this tutorial and read up on opposition surge and heiligenschein. The upshot is that three days shy of full the moon is only perhaps a quarter as bright as it is at full moon, and happily we were able to see quite a bit.

I didn’t know that when we started out, though, but I knew that we wouldn’t see anything if we didn’t try. Ursa Major was opposite the moon, getting closer to the horizon, and with it some of the best and brightest galaxies in the sky. I spent a few minutes faffing around and managed to get M81 in the field of view. It was dim, but it was there, and our observing run was underway.

Some hazy clouds were skirting the northern horizon, and I was worried they might come south and ruin things for us. Also, after the frustrating chase and unimpressive view of M81 we needed a win, so our next target was the Double Cluster, NGC 869 and 884. They were spectacular–two brilliant knots of stars in the rich Milky Way starfields of northern Perseus.

After that we hit some other summer and fall “best of” objects, including the Andromeda galaxy (M31), the Great Glob in Hercules (M13), the Ring Nebula (M57), and the Dumbbell Nebula (M27). Next to M31 we caught the brighter and more compact of its two Messier satellite galaxies, M32. I don’t know if M110 would have been visible or not. It’s a tougher catch, especially under less-than-perfect skies, and I didn’t waste any time looking for it.

M13 was an easy catch, and we kept running up the magnification to see if we could get it to resolve at all. Doug’s 6mm Expanse yielded 67x and, we thought, some tantalizing hints of detail. We Barlowed it up to 133x and the cluster took on the slightly grainy texture that is often the most resolution one can get in a small scope. We also tried lots of magnifications on the two planetary nebula, M57 and M27. We could only glimpse in averted vision the slightly darker center that makes the Ring a ring, and the Dumbbell showed the barest hint of its bilobed structure.

After that we turned back north and plied the starry Milky Way between Cassiopeia and Perseus. Cassiopeia is just lousy with asterisms and open clusters; the only ones we bothered to identify were M103 and nearby NGC 663, which is bigger and brighter.

A highlight of the evening was sweeping the Alpha Persei Association with binoculars. It’s really seen best this way–very few telescopes have a wide enough field of  view to show more than a small part of it. I once read a description of this big, close cluster–variously catalogued as Melotte 20 and Collinder 39–as a “vast wonderland of far-flung suns”, and I can’t look at it without those words coming to mind.

Since Perseus was now a good way up the sky I thought it would be worthwhile to track down the open cluster M34. I’m glad we did. When Doug looked at it he said, “I know this cluster–I’ve drawn it!” And he had–his sketchbook recorded the fingerprint-specific arrangement of stars that make up the cluster. I was most impressed by this–by the drawing and his visual memory both.

At this point we were winding down a bit and just scanning around with binos, taking things as they came. Halfway down the western sky I found the brilliant blue-white double star 16/17 Draconis. By this point Doug’s green laser pointer was fading a bit from cold and overuse, but with some yammering and gesticulating on my part–and much patience and good humor on his–we were able to get both pair of binos on target. That really is a gorgeous double, and just wide enough to be clearly split in low-power binoculars. I recommend it.

Our last stop of the night was the Pleiades, which had just climbed over the northeastern horizon. They were stunning, as always. That gave us a total of nine Messier objects, three non-Messier NGCs (663, 869, and 884), another big open cluster (the Alpha Persei Cluster), and a double star. So, 14 objects in all, which is pretty good for a two-hour session under any conditions.

Using the SkyScanner was a revelation. I had taken a few brief peeks through Terry Nakazono’s SkyScanner on our Baldy runs, and been impressed, but I’d never gotten to just pick one up and freewheel. And “freewheel” is a pretty good description of what we were doing. The scope is light enough that you don’t think twice about just picking up one-handed and moving it wherever you need it. At the same time, four inches is a lot of aperture, and I was consistently impressed by how much the little scope could do, both in terms of light-grasp and resolution. Doug must have collimated it to within an inch of its life, because the image was still good at 133x–a real achievement in any small, fast Newtonian. Finally, I didn’t notice any issues with the focuser. This is one of my pet peeves. Fast scopes have steep light cones and it takes a precise focuser to consistently hit focus without going past in either direction. One of the things that drove me crazy about the Celestron FirstScope was the lousy focuser, which consistently overshot focus. So when I say the focuser on the SkyScanner didn’t draw attention to itself, that’s a good thing. I’m sure that like all consumer scopes there’s some sample-to-sample variation with the SkyScanner, and Doug’s might be an unusually fine example, but so far both of the SkyScanners I’ve gotten to use have impressed me. I think I’ll get one for the Suburban Messier Project, which is on hold until it cools off some–it was 107 here today. In October!

Oh, and speaking of the Suburban Messier Project, I was most impressed by the quality of Doug’s sketches, and by the fact that, having sketched something once, he could recognize it at the eyepiece later without knowing in advance what it was. I’d like to have that level of familiarity with these objects, and I intend to get it–by sketching them. Stay tuned.

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Guest post: A few thoughts about the Orion SkyScanner and other scopes, including the Bushnell Ares 5

July 8, 2012

Here’s the first guest post by frequent commenter and dedicated deep-sky observer Terry Nakazono. Actually “dedicated” is an appalling understatement, since Terry regularly challenges himself and his scopes by (1) observing faint deep-sky objects, mostly galaxies, (2) with small scopes he can carry on public transportation and by foot, (3) from light-polluted skies in and around Los Angeles. I’ve been looking forward to reading about Terry’s scopes and his observing techniques, so this guest post is most welcome–hopefully there will be more to follow.

I’ve been using the Orion SkyScanner the past 2 years for nearly all of my deep-sky observing needs because it’s so easy to transport and set up – crucial if you rely on public transport and your own two feet to get to darker sky sites. For a package weighing in at 6.2 lbs with scope and mount combined, 100mm of mirror is a lot of aperture.

Both scope and mount fits snugly in this Adidas Schmidt backpack. All that’s needed is a tripod to attach the mount to, and a solid Manfrotto weighing in at only 4.5 lbs. (but with a 15.5 lb. weight load capacity) provides a strong, stable support.

Factor in the eyepieces, star charts and other accessories, and you’re only transporting about 12-13 lbs. of equipment on your body. By comparison, the Orion StarBlast 4.5 weighs 13 lbs, while the Orion SkyQuest XT4.5 is 17.6 lbs. Both cost about twice as much ($199.99 and $239.99, respectively) as the SkyScanner ($109.99) and both add only 14mm of additional aperture to the mirror. As Joe Roberts says, you will not likely find a scope that will show more for the cost.

For deep-sky work, superb optics isn’t as critical compared to planetary and double star work, so a 100mm Newtonian reflector works well (for me). Despite not having a collimatable primary mirror, collimation can be achieved by center spotting the primary mirror and adjusting the tilt on the secondary with the help of a collimation cap, significantly improving the views of the planets and double stars as well as deep-sky objects.

Here, you can just see the notebook reinforcement ring I put on the center of the primary mirror; the secondary mirror is collimated by adjusting the three allen screws surrounding the main screw in the center of the secondary holder with an allen-head screwdriver.

Having said all that, I’m no longer wedded to the SkyScanner as my sole dark-sky instrument.

I now have an Orion shoulder bag that I can carry my Orion VersaGo II mount and Bushnell Ares 5 in.

I also have a Vixen Mini-Porta mount which will support my Celestron C90 Maksutov-Cassegrain (C90Mak, top) and Orion ShortTube 80-A (ST80A, bottom) telescopes. I just ordered a smaller Orion shoulder bag that will carry the aforementioned mount and one of these two scopes. These Orion bags are ergonomically well-designed and make it easy to carry both scope and mount over your shoulder without causing major strain.

I suspect that despite their better optics, both the C90Mak and the ST80A will not allow me to see “deeper” into space (i.e. detect fainter objects) than the SkyScanner. But I’ll need to perform a “shoot-out” between these scopes outside of light-polluted urban skies to confirm.

Right now, I see the collapsible tube Bushnell Ares 5 (BA5) as the scope that will eventually replace the SkyScanner as my deep-sky instrument once I’ve gone as far as I can with the latter. This is an F/5 130mm Newtonian which thanks to its unusual design, weighs only about 6.5 lbs. for the OTA. At only $164.99 (with no shipping or sales tax) from Optics Planet, this is probably the best scope deal in the country right now.

Here is the scope with the tube collapsed, mounted on an Orion VersaGo II (because of its bulkiness, I’ve discarded the 6.5 lb. tabletop mount that came with this scope).

And here is the scope with the tube extended all the way out.

I’ve created a light shroud made out of black felt to cover the open tube and protect it from the elements while observing.

In the limited amount of time I’ve used this scope in both light-polluted and semi-dark skies, I’ve had a tantalizing taste of what 130 mm. of light gathering power can show. In my light-polluted front driveway with direct vision, I was able to see the ring shape of M57 for the very first time, using only 65X magnification. With the 100mm SkyScanner, I can barely make out shading within the interior of the oval-shaped disk at 80X or more using averted vision in darker skies. Less than two months ago, I took my BA5 out to a semi-dark (orange-zone) site for the first time. M13 looked nothing like the views I saw through the SkyScanner – at 130X, this globular was just exploding with stars all over the place. Ditto for M5.

As Matt has shown us through his reports on using “Stubby Fats” in the desert, you can do some serious deep-sky observing with a 130 mm F/5 Newtonian in semi-dark or dark skies.

But the BA5 has to wait until I’ve exhausted all the possibilities of the 100mm F/4 SkyScanner.