Archive for the ‘Gear’ Category

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

February 11, 2017

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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

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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.

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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.

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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.

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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.

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Here’s the scope before…

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…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.
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Upgrading secondary collimation bolts on a reflector

February 5, 2017

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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.

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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.

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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.

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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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Marking up sky atlases

February 4, 2017

I’m a book lover. Any space I’m in for long will have books on every available surface and piles of extras on the floor. Because of this love of books, for a long time I wouldn’t mark them up. This hands-off reverence extended to my sky atlases. But eventually I realized that sky atlases are tools, not heirloom pieces, and anything that makes them more useful when I’m observing is justified.

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Here’s a representative page from my working copy of the Pocket Sky Atlas (I also have a second copy, autographed by John Dobson, that actually is an heirloom piece now). The circles and polygons flag objects from various Astronomical League observing projects. Triangles are double and multiple stars, rectangles are Herschel 400 objects, big circles are for the Binocular Deep Sky objects, and an open letter C designates Caldwell objects. I also drew in the position of Almach, which is just off the edge of this chart, wrote in the number for the multiple star 57 Persei, and wrote down the magnitudes of Algol and some of the useful reference stars, including Almach. Arrows in the margins are left over from my Caldwell tour.

I’ve finished all of those projects except the Herschel 400. You’ll see that some of the little rectangles have a diagonal slash across one corner – that’s how I flag which ones I’ve already observed. I’ve actually seen all of the H400s on this chart, I just got lazy about marking them off in the atlas. But I did write ‘CLEAR’ in the corner of the page so I know not to waste my time looking for unobserved H400s here. Other pages have the numbers of the H400s I still need written in the margins, for quick sorting and bookkeeping at the eyepiece.

These marks are very helpful while I am working on a project, because I have an instant visual reminder of what’s available to see in any given stretch of sky. And once I’m done with a particular project, the marks still point me to a lot of ‘best in class’ objects that I might otherwise overlook or forget.

Oh, I also sketch in the positions of comets from time to time, with the dates of observation.

This method has worked so well for me that I have thought about picking up extra copies of the PSA (for $13!) just so I could mark them up with objects from other observing projects. I’ve done that with a couple of my other atlases. My copy of the Cambridge Double Star Atlas has all of the AL Binocular Double Star targets marked, and I use my Jumbo PSA (which is ridiculously useful) to keep track of targets from the last several years of Sky & Telescope’s Binocular Highlight column, to help me avoid repeats. Of course I have other lists for all of these things, both physical and digital, but it’s nice to have an easy reminder when I am out observing or doing desk research.

Do you mark up your atlases? If so, what system do you use? Let me know in the comments.

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Unboxing the Bresser Messier AR102S Comet Edition

January 31, 2017

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I’ve been interested in this scope since late 2014. The Celestron TravelScope 70 turned me on to the joys of refractors back in 2012, which led to the C102, which led to the C80ED, which got me firmly hooked on low-power, widefield scanning, which led to this.

This is the Bresser Messier AR102S Comet Edition, which I believe is a record for the longest name of any telescope I’ve owned. And you actually do need all of it, because there is another Bresser Messier AR102S that is a completely different scope. That other AR102S is a standard f/6 achromat. The AR102S Comet Edition is an f/4.5 rich-field scope. And as you can see from the photo, it’s built funny. Instead of having the focuser at the back end of the tube, the focuser is mounted on the side of the tube, as in a reflector, and a reflector-style secondary mirror* bounces the light from the objective lens to the eyepiece. This makes for a very short, compact scope, and theoretically for easy collimation via that secondary mirror (I haven’t tried that yet). Scopes like this are sometimes called “reflactors” because they combine an objective lens with a secondary mirror. I’ve seen ATM builds using this design, but I’ve never seen another one marketed commercially.

* Existential telescope question: is it still a secondary mirror if there’s no primary?

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As far as I know, this scope has only ever been sold as part of a travel kit that includes the OTA, an eyepiece, an alt-az mount, 7×50 binoculars, and a backpack to carry it all. That package has a list price of $349, but the list price has been creeping downward. Explore Scientific’s online store and OpticalInstruments.com both carry the AR102S Comet Edition (man does this scope need a nickname) package for $299, but B&H Photo-Video has it for $249 with free shipping. Amazon used to have it for $249 as well, but I seem to have gotten the last of those – as of this writing, the price is hovering in the $340s.

I’ll have a first light report along soon, this one is mostly photos of the unboxing and the scope.

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Outer box…

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…contains the middle box…

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…contains the inner box. That’s right, three boxes before you get to anything other than packing material and the instructions.

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Inside box number three are the backpack and two more boxes.

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Inside the backpack is the OTA in a plastic bag, and on the right you can see the eyepiece peeking out of the side pocket.

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Oh, also in the backpack are the 7×50 binos. Everything bagged.

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And inside the bags, the telescope OTA with wrapping paper, the binocular case with the binos in yet another plastic bag inside that, and the eyepiece bolt case with the eyepiece in yet another plastic bag inside that. Oh, and a couple of hex wrenches inside the bag with the bolt case, for collimating the OTA.

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And here’s everything finally outside of the various bags, bolts, and cases.

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The OTA is 20″ long and 4″ in diameter, with a 4 1/4″ diameter dew shield. In the shots before this one, you can see the dovetail on the right side of the OTA, and here you can see the shoe for a finder (not included) on the left side of the OTA. Having the dovetail on one side and the finder shoe on the other is convenient, because it means the OTA can’t roll over and bang the focuser if you set it down on a flat surface.

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Here’s the lens cap. If you’re thinking it looks like a Meade, you’re not wrong.

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And way down inside the dewshield, 4 1/4″ in, is the objective lens, with its dark green anti-reflection coatings. The achromatic doublet is fully multicoated. The dewshield has an outside diameter of 4 1/4″, and an inside diameter of 4 1/8″. Past the objective lens you can also see the single baffle inside the OTA, which is otherwise just painted flat black inside.

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Remember those other two boxes? The long one has the tripod and the short one has the alt-az head.

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The alt-az head, which is metal, and the eyepiece tray, which is plastic.

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The mount assembled. The alt-az head looks like my SkyWatcher AZ-4/Orion VersaGo II, but it lacks the adjustable tension knobs.

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Here’s a feature that I really like: the eyepiece tray goes solidly onto the spreader bars with no tools. It threads over a central bolt, and then rotates to snap into position. This is super-handy at the end of the night, because I can unlock and rotate the eyepiece tray without taking it off, and fold the tripod legs in just enough to get through the door.

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The whole rig set up. The tube looks not quite square here, but that’s just field distortion from the iPhone camera, which we’ve seen before here.

The OTA weighs 6.2 lbs, the mount weighs 6.8, so the whole rig clocks in at 13 lbs even. That’s pretty portable, although certainly at least flirting with being undermounted. More on that in the first light report.

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User end. The eyepiece is a Bresser 20mm 70-degree model, which is currently on sale for $40, down from $60, at OpticalInstruments.com. If you’re thinking that $60 seems like not much money for a new fully-multicoated 70-degree eyepiece, I agree, and I am likewise suspicious. I assume it’s some kind of Erfle, but I haven’t taken it apart to confirm. The size, form factor, and even barrel detailing are very similar to Orion Sirius Plossls, but the eye lens is just slightly too big for Sirius dust caps to fit (which is a shame, since it gets in the way of me stuffing this thing in my pocket while I swap Plossls and Expanses around). It gives 23x and a 3-degree true field of view.

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Here’s the left side of the back end, showing the finder shoe, the collimation bolts for the secondary, and another look at the focuser. The focuser is an all-metal rack-and-pinion job. Oddly enough, the focuser drawtube is 2″ in diameter but the 1.25″ adapter at the top is permanently mounted. So it’s a 2″ focuser that only accepts 1.25″ eyepieces. I think there’s a reason for this – the focal plane is 6-7 inches (150-175 mm) away from the center of the OTA, which means at least a third of the 459-mm light path occurs after the light hits the secondary. I think a 1.25″ drawtube would cut into the light path and stop down the scope.

The finder shoe is not one I’m familiar with. Almost all of my experience is with gear made by Synta (Orion/Celestron/SkyWatcher), which uses the same mostly-but-not-quite industry standard dovetail shoe for finders. This is a weird square rig that is outside my experience. I probably won’t use a magnifying finder – I can get by okay just dead-reckoning, and when I feel like cheating I can lay a laser pointer along the dovetail shoe or the square edge of the focuser and get on target very fast. But I might put a counterweight there, to get the balance point a little farther back so the eyepiece height would change less going from horizon to zenith. Or here’s an interesting thought: I bet I could gin up an eyepiece rack that would attach to the finder shoe. That would be cool, convenient, and a counterweight.
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Here’s the focuser again, with the axis drawn in blue. This is to make a point. I’ve seen one or two folks on Cloudy Nights alleging that this is a “leftover scope” – that Bresser/Explore Scientific had some leftover tubes, leftover secondaries, and leftover focusers, so they cobbled it all together into this Frankenscope. But that doesn’t hold up. The focuser is a single-piece aluminum casting with two features of note. First, it wraps tight to the 4″ diameter tube, which if it was leftover from a reflector would have housed a smaller-than-4″ mirror. There are 3″ reflectors out there, like Orion’s SpaceProbe 3, but no-one puts 2″ focusers on them. Second, and more importantly, the focuser knobs point across the tube on this scope – that’s what the blue line shows in the image above – as opposed to down the length of the tube as in all mass-produced reflectors. Again, the focuser is a single chunk of aluminum – the 2″ tube can’t be separated from the base, or rotated relative to it. So I’m confident that this focuser was purpose-built for this scope.

The “leftover scope” idea was pretty dumb anyway. The most expensive part of any refractor is the objective lens, which has to be figured to a tolerance of a millionth of an inch. The rest is just steel, aluminum, plastic, and fasteners, which cost peanuts by comparison. As far as I’ve been able to tell, neither Bresser/Explore Scientific nor their parent/partner Jinghua ever sold a 4″ f/4.5 scope before. It doesn’t make any sense to figure a bunch of bespoke objectives – the expensive part, especially after full multi-coating – just to sell the cheap hardware.

So, somebody decided that a fast, 4″ reflactor was a good idea. Were they right? Tune in next time and find out.

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What’s in my eyepiece case

January 9, 2017

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In the 9.3 years I’ve been stargazing, I’ve had three eyepiece cases. The first was a Plano tackle organizer with a thin layer of bubble wrap taped into the lid, which held half a dozen 1.25″ eyepieces. After that I got one of the cool foam-lined purpose-built eyepiece cases that Orion and everyone else carry, but that one didn’t last long – probably less than a year. The problem was that although it did a fine job of holding the eyepieces, it didn’t have room for all the other stuff I wanted to cram inside.

Then in 2012 or so I got the eyepiece case that I’m currently using, and the one that I’ll probably be using for a long time to come. It’s not bespoke – it’s a $20 Craftsman toolbox I picked up at Orchard Supply and Hardware. I think this particular model has been discontinued, but there is something almost identical on the shelves today, and there probably will be from now until the end of time (or at least civilization). This one is probably the current incarnation, and hey, it’s only 10 bucks and has a better latch.

The exterior doesn’t deserve much comment. I put my name on it, and its contents, mostly to make it clear to anyone who might find it among my stuff if they’re going through the garage looking for tools of the terrestrial variety. I don’t fully trust the single latch so I keep a zip tie run through the hole where the lock would go. The zip tie goes in the top shelf when the case is open.

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The top shelf, which is removable, holds my red flashlight, Astro-Tech dielectric diagonal (previously discussed in this post), eyepatch, Barlow, and quick-look and outreach eyepieces – various Plossls, the 6mm Expanse, and the dreadful 4mm VITE that I haven’t yet thrown away. Not shown in the photo are a spare pen and a little Sharpie, both buried under the bag containing the diagonal. You can see that all of the eyepieces are still living in the boxes or cases they came in, and they’re held in place against rocking or tipping by a thick layer of bubble wrap taped into the lid of the tool box.

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Another sheet of bubble wrap sits below the top shelf and cushions the gear in the bottom of the toolbox.

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The bottom of the toolbox holds my ‘top shelf’ eyepieces and a lot of spare gear besides. The three Explore Scientific eyepieces came clamshelled in foam, and each one rests in the bottom half of its original clamshell. One of the top halves forms a bed for the 5mm Meade MWA. The two slots in the middle used to hold my Stratus eyepieces before I let them go – the ES models are smaller, easier to handle, and do a significantly better job. Now those slots hold the 32mm Astro-Tech Titan, my only 2″ eyepiece, the GoSky iPhone adapter I blogged about here, and a cord to hang my eyeglasses when I’m observing.

Around the edges I have all kinds of stuff crammed into the spare spaces. Clockwise from the top:

  • Contact info, just in case the case ever gets lost and found by someone decent. Has my name, address, email, and cell number.
  • Lens cloth, just in case.
  • Spare AAA batteries for the green laser, the red flashlight, and the laser collimator.
  • A ziploc. Never know when you’ll want a small waterproof bag. Sometimes holds spent batteries if I have to do a field swap.
  • Laser collimator. Reminds me, I need to blog sometime about how to collimate a laser collimator.
  • A set of hex wrenches for collimation.
  • Small pliers for the same purpose – I’ve swapped the hex bolts on a lot of scopes for standard hex-head bolts that I can tweak with pliers. Much better than farting around with hex wrenches.
  • Green laser. Super-useful when stargazing with newbies and old hands alike.
  • Tiny atlas – so I’m never without one. This is the Collins Gem Guide to Stars, which has little charts of the constellations and a short list of the most impressive DSOs for each one. Unlike Sky & Tel’s Pocket Sky Atlas, this thing truly is pocket-sized, and small enough to take up essentially no space or weight in the case. It has saved my butt a couple of times when I forgot all other atlases.

There is one other thing. In the third photo you can see a light blue bag through the intermediate layer of bubble wrap. I think that’s the bag the eyeglasses cord came in. Now I use it to hold a set of iPhone earbuds, which serve as a remote trigger when I’m taking pictures with the iPhone adapter, as shown and explained here.

That’s it – an inexpensive, sturdy, and above all roomy case for my eyepieces, with nooks and crannies for a whole lot more.

What’s in your eyepiece case?

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SkyScanning in Utah – and Claremont

July 25, 2016
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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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Binocular Highlights: what I’m rolling with

July 23, 2016

I just turned in my sixth Binocular Highlight column for Sky & Telescope. While I had everything out for the write-up, I thought people might be interested to know what sources I make use of.

Here’s the stuff I use pretty much every time:

  • S&T’s Pocket Sky Atlas and Jumbo Pocket Sky Atlas. I usually take a full-size clipboard and Interstellarum out with me to observe, so the Jumbo version is no added hassle. Consequently – and perhaps counterintuitively – I tend to use the Jumbo version for nearby excursions, and the classic for desk reference and travel. This is usually my first stop.
  • interstellarum Deep Sky Atlas: Desk Edition. Despite the name, my primary ‘deep’ field atlas. Goes out with me practically every time, unless space is really at a premium. Also sees heavy use indoors for planning sessions and following up on things.
  • Chandler Night Sky planisphere. Hands down, my most-used tool – it goes out with me every session no matter what, and I frequently refer to it indoors as well.
  • Chandler Sky Atlas for Small Telescopes and Binoculars – particularly useful for the Milky-Way-centric chart that shows the galaxy as a flat band with the celestial coordinate grid deformed around it. Useful for thinking about where things are with respect to the disk of the galaxy, for quick looks, and for the object list.
  • SkySafari 5 Pro app on my iPhone. Astounding amount of information. Usually my first source for looking up distances, separations, etc., although I always confirm with some other source.

Sources I turn to often, but not always:

  • Glenn LeDrew’s atlas of the Milky Way in The Backyard Astronomer’s Guide, 3rd Edition. I already had the 2nd edition – it was one of the first books I picked up when I first got into amateur astronomy back in 2007. I got the 3rd edition primarily for the Milky Way atlas, and I was not disappointed. The identification of OB associations is particularly useful.
  • The Cambridge Double Star Atlas. Super helpful for checking on double stars, and a handsome and useful atlas all around. Also, kind of an insane steal at $22 on Amazon.
  • Burnham’s Celestial Handbook. Not my first stop for astrophysical data, but it’s nice to get some historical perspective and Burnham excels at this.
  • O’Meara Deep-Sky Companions series. Useful for astrophysical info, historical persepctive, and visual impressions from one of the world’s foremost observers. Crucially, O’Meara usually describes how objects look at varying magnifications, including naked eye and binocular appearances, so although the books are grounded in telescopic observations they are still quite useful for binocular observers.
  • Uranometria, All Sky Edition. Always nice to have the big gun in reserve, although I find Interstellarum more useful for most practical applications.

To get the latest astrophysical data I turn to the web. Particularly helpful sources are the SEDS Messier database, non-Messier NGC/IC/etc page, and Interactive NGC Catalog, the NGC/IC ProjectSIMBAD, the NASA Extragalactic Database, and if all else fails, Google Scholar and ArXiv.

For inspiration I’m quite omnivorous. Gary Seronik hit the Messiers pretty hard for the last few years, so I’m avoiding them for the time being, both to avoid duplication and to force myself to go find new stuff. The Astronomical League’s Deep Sky Binocular observing list (free), the Irish Federation of Astronomical Societies Binocular Certificate Handbook (free), James Mullaney’s Celestial Harvest, Phil Harrington’s Touring the Universe through Binoculars, and my own notes compiled over the past 8.5 years all serve as jumping-off points. Tom Price-Nicholson’s Binocular Stargazing Catalog (free) looks like a useful source as well, although I haven’t had a chance to explore it thoroughly yet. More often than not, I go out to find a particular object or to survey a set of objects (open clusters in Cygnus, for example) and end up discovering new things. So far I’ve been generating many more possible topics to write about than I actually can, so it seems unlikely that I’ll run out of subject matter anytime soon. We’ll see!

If you know of something I should be using that’s not on the list, please let me know – the comment field is open.

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My 9.5-pound observatory

June 27, 2016

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In the last post I introduced my new small scope, the PICO-6 60mm Mak-Cass. After having a positive first light, I decided the scope was good enough to be the center of a new travel observing kit. Here’s the scope mounted on a Universal Astronomics DwarfStar alt-az head and a Manfrotto CXPRO4 Carbon Fiber Tripod.

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Here’s the kit broken down. The case is an AmazonBasics Medium DSLR Gadget Bag, which Doug Rennie helpfully put me on to. The Pocket Sky Atlas and small Night Sky planisphere go in the back pocket. In front of the bag from left to right:

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Here’s everything packed away. This was just a first pass. The final arrangement I came to is as follows:

  • The left-hand slot holds the DwarfStar head with the handle removed and stowed separately, as shown here, and the 6mm eyepiece in its cardboard box, wrapped in a small piece of bubble wrap.
  • The middle slot holds only the PICO-6 OTA, just as shown here.
  • The right-hand slot holds the 32mm Plossl and the 8-24mm zoom eyepiece on the bottom, both of them in the beige metal cases that the zoom eyepieces come in (I had a spare). The tops of the two cases form a horizontal shelf which holds the diagonal, wrapped up in a small drawstring bag.
  • Finally, a piece of bubble wrap goes across the tops of all three slots and gets tucked in at the edges and corners.

Oh, the vertical dividers in the case are held in with velcro so they can be adjusted or removed as needed.

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For flight, the tripod can go in a backpack or in checked luggage, and the AmazonBasics case goes as my carry-on “additional item”. The tripod weighs 3.5 lbs, the fully-packed case weighs 6. For a total of 9.5 lbs, I have a full-size tripod, a smooth, variable-resistance alt-az head, eyepieces giving magnifications of 22x, 29-88x, and 117x, a scope which will show the Cassini Division and split Epsilon Lyrae, a planisphere, and a mag 7.6 all-sky atlas.

Oklahoma dig

This past week I was out at Black Mesa, at the northwestern corner of the Oklahoma panhandle, to dig up dinosaurs. I took the whole kit, and I used it. On Sunday night I showed half a dozen people the moons of Jupiter, the ice caps of Mars, the rings of Saturn, a couple of double stars, and the full moon. Monday night I was too pooped for stargazing. Tuesday I spend a couple of hours observing with my parents and a couple of other visitors who were also staying at the Black Mesa Bed & Breakfast. We looked at the same run of stuff as I had Sunday evening, plus a couple more double stars, the open clusterM7, and the False Comet Cluster in southern Scorpio, which is a visual amalgam of the open clusters NGC 6231 and Trumpler 24. After that, we were clouded out for the rest of the week, but it was still more than worth it to have the little scope along.

Verdict: an amazingly flexible and capable setup. I look forward to many more adventures with it.

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Here’s one more shot from the road. Nothing telescopic – on Thursday morning the rising sun was accompanied by a pair of sun dogs. This is a raw shot with my iPhone 5c. The best sun dogs I’ve ever seen in my life.

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Small telescope quest reloaded: the PICO-6 60mm Maksutov

June 26, 2016

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This came a couple of weeks ago. I got it from Kasai Trading in Japan – here’s the link. They market both a 60mm Maksutov-Cassegrain, which is the PICO-6 shown here, and an 80mm Mak-Cass called the PICO-8. These appear to be the same scopes as those sold in Europe as the Omegon MightyMaks, which are available through Astroshop.edu (here) and Amazon.co.uk (here).

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It’s been a while since I posted about small scopes, and after getting the little SV50 refractor nearly six years ago, I declared my small telescope quest complete. But the SV50 turns out to be a more satisfying finder than stand-alone scope, even for air travel. For deep-sky work when I’m traveling, I’m usually happy with binoculars (most recently on the Channel Islands), but sometimes it’s nice to check on the planets, too, and the SV50 just doesn’t have the reach.

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I thought this little Mak might be just the ticket. As you can see, it is tiny. It weighs just a bit over 1 pound. Here it is with a regular-sized beverage bottle and my largest eyepiece, the 2-inch 32mm Astro-Tech Titan.

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And here it is next to the SV50. The SV50 has a focal length of 210mm and a focal ratio of f/4.2. The PICO-6 has a focal length of 700mm and a focal ratio of f/11.7, which makes it roughly equivalent to the 60mm refractors sold by any number of astro vendors. I actually tested the PICO-6 side-by-side with London’s 60mm f/11.7 Meade refractor. The refractor threw up a brighter image – no shock there, since it’s unobstructed and has no mirrors to reduce light-throughput. But much to my surprise, the PICO-6 was a hair sharper: it could resolve fine details and split close doubles beyond the reach of the refractor. The differences weren’t dramatic, but they were there.

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The PICO-6 comes with a dovetail bar and a brass compression ring in the visual back. Both required a bit of work. You can also see two of the three collimation screws in this photo.

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I could not get a diagonal to seat in the visual back. After some investigation, I found that the brass compression ring could not fit neatly down into its groove. It had been poorly made, and had an extra flange of metal in two places that made it wider than the groove. It was the work of 5 minutes to grind down the extra width with my Dremel, but it’s still pretty disappointing. I don’t know how these things are made, but it seems unlikely to me that anyone could have seen this and not known that it was a problem.

Also, on the Kasai Trading “Dear Customers” page (here), under the heading “Quality Inspection” it says (courtesy of Google Translate):

Astronomical telescope of our handling is through the “Jisshi inspection” all by Kasai will be shipped to the customer. This is a test carried out by actually seen the night of stars, most practical-world, but the one that is adopted for performance is a test, it takes time and effort, also takes place on the night of good clear weather of seeing because it can not be accurate inspection unless, depending on the weather will give sometimes can not keep our promise of delivery date. Excuse me, please understand that effect.

That makes it sound like all of the scopes are star-tested before they go out to customers, but that clearly is not the case, because the scope I received was unusable until I fixed the visual back.

UPDATE: I was mistaken. According to Mr. Kasai in an email to a Cloudy Nights user, all of the scopes are tested before they ship out, but when they test them they unscrew the visual back. Here’s the key quote, and the “somebody” he’s referring to is me:

Also I dare to emphasize the fact that we do perform visual test on each unit with artificial stars – to check the residual aberration, collimation and mirror shift. Somebody who bought PICO-6 suspected us of this fact, as the brass ring in the eyepiece adapter was bent and it couldn’t accept an eyepiece easily. I feel sorry we forgot to check this defect on this case, but still this has nothing to do with our visual test.

Full message here.

So, I guess they do test them all. I still think it’s dumb to test all the scopes optically but not mechanically – sending out a scope that is unusable until one of the parts has been further machined is arguably worse quality control than sending out a scope has some spherical aberration. But at least they are optically tested, and I retract my claim that they aren’t.

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The dovetail bar is also a bit wonky. It’s a couple of millimeters narrower than the Vixen/Orion/Celestron standard, so it will fit into a standard dovetail slot, but you really have to trust the thumbscrew because it will be the only thing holding the scope into the mount. I solved this by putting the scope on a dovetail shoe for the pistol-grip ball head shown here – by design or coincidence, that shoe is a good fit for standard Vixen dovetails. With the help of that shoe, I was able to use the scope with my Universal Astronomics DwarfStar alt-az head. More on that soon.

Now, it may sound like I am down on this scope. I’m not. I wish the quality control was a little higher, but the problems were not unfixable. At least for me, with almost nine years of experience tinkering with telescopes – I can’t recommend this scope for anyone who isn’t prepared to do some work on it. And optically it’s okay. It arrived out of collimation, but with a little help from Polaris I was able to get it tuned up enough to catch Saturn’s Cassini Division and split Epsilon Lyrae cleanly into all four components at 117x. After the mechanical difficulties with the scope, that was a welcome surprise.

Then I flew with it, but that’s a story for the next post.

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Getting ready for Mercury

April 18, 2016

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The planet Mercury will transit the sun on the morning of Monday, May 9. Mercury transits are not as rare as the more famous transits of Venus, but they still only come around once or twice a decade on average. The last Mercury transits before this one were in 2003 and 2006, and the next two after this year will be in 2019 and 2032. From southern California, the transit will already be underway when the sun rises at 5:57 AM, maximum transit (the point when Mercury is the furthest inside the sun’s disk as seen from Earth) will be at 7:58, and Mercury will exit the sun’s disk between 11:39 and 11:42 AM (all times in PDT).

For the transit of Venus in 2012, I used a simple homemade device called a “sun funnel” attached to a small reflecting telescope to project an image of the sun. You can read more about that here and here. The sun funnel worked well enough – I also used it for the annular eclipse in 2012 and the partial eclipse in 2014 – but the screen material degrades the resolution somewhat. Mercury is a lot smaller than Venus, and much closer to the sun, and both of those factors make it appear much smaller than Venus during a transit.

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I want maximum resolution for observing and photographing the upcoming transit, so I finally sprung for a full-aperture solar film filter for my 80mm telescope, which you can see set up at the top of this post. I got it out the other day for a test drive and got some decent photos of the current large sunspot AR2529, shown above. I’m pretty happy with the results – now if we can just get clear skies on the morning of May 9. If you’re curious, the filter I got is the GoSky Optics full-aperture filter with Baader solar film. There are several sizes available to fit all kinds of telescopes, and the filter attaches securely to your telescope tube or dewshield with three nylon-tipped screws. I got the filter for telescopes 81-113mm in diameter (outside tube or dewshield diameter, not optical diameter!), which is currently a little under $50 on Amazon.

This is my second GoSky product, after the universal cell phone adapter I picked up last fall, and I’ve been impressed with the solid construction and good fit-and-finish of both products. Some of the weird large-scale blotchiness in sun photos is probably either distortion from the iPhone’s tiny field lens, or gunk on the surface, and the uneven margin of the solar disc is from atmospheric turbulence. But I think the graininess across the surface of the sun is actual solar granulation. I couldn’t see it on the iPhone – not enough image scale. If I had, I’d have thrown in a shorter focal length eyepiece and tried some higher-magnification shots. They might not have turned out well even if I had taken them – the seeing was pretty awful – but it would have been worth a shot. Something to try next time.

The diameter of the sun is 109 times that of Earth. Here's how Earth would compare to the current large sunspot if they were side-by-side.

The diameter of the sun is 109 times that of Earth. Here’s how Earth would compare to the current large sunspot if they were side-by-side.

Unfortunately, I won’t be here in California to share the transit with my local friends and fellow observers. I’ll be in Utah chasing dinosaurs from May 4 to May 14, so I’ll have to catch the transit from there. I’m driving up and bringing my 80mm scope to take advantage of dark Utah skies in the evenings. If you want to plan your own transit observation, or just want to investigate how the transit will appear from various points on Earth’s surface, this interactive map is excellent. And if you need safe, inexpensive ways to observe the sun, check out my page on safe solar observing. Clear skies!