Archive for the ‘Hacks’ Category

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Guest post: David DeLano’s ultimate Galileoscope quest, Part 4 – The GS F11 SCT GS to end all GS

March 9, 2014

The moment you’ve all been waiting for–I would be shocked if anyone, anywhere, ever, has put this much time, thought, experimentation, and additional gear into their GS. But having used it in the field, I can tell you that David’s monster GS is both a potent observing tool and a real pleasure to use. To see how David got from the stock GS to this, see the previous posts in this series.

GS F11 SCT

There is actually one other way to solve the Galileoscope focal length issue. When the Learning Encounters site (http://www.leosciencelab.com/ [not linked here because there is nowhere to go–MW]) was functional, they carried a diagonal kit, with which you could construct your own diagonal to go with your Gallileoscope. Part of the kit was a new, F11, objective. With this longer focal length objective, a diagonal will work in the GS without shortening it. This is the ideal solution, but it is likely very difficult to find one at this point. I had modified my daughter’s GS with this kit, and it worked perfectly well with a Stellarvue diagonal w/helical focuser. I also had a spare kit, originally bought for my son, but he lost interest. So, I decided to use it for myself.

Somewhere along the way in this project I also bought a used SCT focuser off of Cloudy Nights. The SCT focuser ended up to be a lot larger than I had thought it would be. It was far to long to use the original F10 objective, but since I had the F11 objective I decided to give it a try.

I had a 2″ adapter with SCT threads from my previous experimenting. I had to buy a M-M ring to mate it to the focuser, and the first one I tried didn’t quite work. I found a second one that had a lower outer profile, and it actually nestles inside the focuser barrel so that the 2″ adapter and focuser are mated with no additional length. I tested this out, and it was almost short enough to focus, but not quite. The SCT focuser has a 2″ EP holder on it, and I used the shortest 2″ to 1.25″ adapter I could find, but was still in need of a couple mm in length. I also found that the tube was butting up against the inside of the 2″ barrel, so I shortened that a bit (and at this point it barely touches, which is the best length to have), but I was still not satisfied. I found a prism diagonal with a lower profile EP holder, but was still not quite satisfied. I found a 2″ to 1.25″ adapter at ScopeStuff that was almost zero clearance. It would be zero clearance with an EP but since I was attaching a diagonal, it added 1-2mm. ScopeStuff, however, removed the lip on the adapter for a small fee, and this gave me the focal length I desired – I can focus with my glasses on or off! The adapter attaches to the diagonal barrel with a couple of inset hex screws, which works perfectly.

I added a more than necessary red dot finder that I had bought cheap somewhere along the way. It looks like overkill, but actually helps with the balance. This scope is really too much for a finder, though I did use it while observing at the Salton Sea with Matt. It will likely end up as my lightest grab and go as the mount it is attached to in the picture rides on a photo tripod, and both the scope and tripod fit into a bag together. All that is needed is an EP or two. As a finder, I had been permanently using a 32mm Plossl, but as a viewing scope I’d likely take along a couple of other EPs to use.

Modded GS compared to GS F11 SCT

Side by side with Matt’s modded GS you can see that it is about 50mm longer, which is what the F11 objective gives you. The SCT focuser makes it look even more massive, but it still is a GS at heart.

And also to give some comparison, here are, top to bottom, the SCT set, Matt’s set, and the ABS part, so you can see how much focal length each adds.

attachment comparison

I think I’ve covered everything. If you are still reading this, I hope you enjoyed the ride. If you have a Galileoscope kit, I hope that I have inspired you to turn it into a usable scope or finder. If you have questions, please post them to the blog comments, and I’ll try to clarify.

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Guest post: David DeLano’s ultimate Galileoscope quest, Part 3 – The Difficult Solutions

March 2, 2014

The third installment in David DeLano’s GS-hack-a-thon guest post series. For the rest of the series, click here.

To make the Galileoscope really useful you need to have a better way to focus it, and need to be able to use a diagonal with it, for comfort of viewing. These are difficult problems to solve, but hopefully the information given here will resolve these issues in a relatively easy fashion. I’ll give a little bit of the process I went through to come to a usable solution, to help others come up with their own solutions. At the end, I’ll give what should be an off-the-shelf solution, though I have not used it myself.

First, the focus issue – the only reasonable solution is to find a helical focuser, though in the next post I’ll show another possible solution. When I first started looking for a helical focuser, they were difficult to find, at least at a reasonable price. I eventually found a diagonal with a helical focuser at Stellarvue, but only by sending them an email and asking if they had any available standalone, as they packaged it with one of their finders. Now, however, I see that they have them on their web site, so hopefully they will remain available for anyone wanting to mod their GS.

You might ask, why not just use the diagonal with the helical focuser with a Barlow lens attached, and not have to mod anything. Well, I tried this. It was a bit baffling at first, and I could not get the focus to really do anything. Then it occurred to me…by lengthening the distance between the Barlow lens and the EP lens, all I was doing was changing the magnification due to the Barlow lens. I would still need to use the push-pull focus.

StellarVue diagonal

Stellarvue diagonal, from the Stellarvue website.

I should also note that I have received two different helical focusers from Stellarvue. The original one “worked”. The newer ones have more travel, but add a bit more to the focal length, and won’t work for all cases. What this really means is, you need to find a focal length solution that takes into account this additional length.

Now on to the real mod work. The focal length needs to be shortened. I wish I could tell you how much the length needs to be shortened, but measuring the light path is not as easy as it sounds, especially through a diagonal. I should also note that this diagonal has a prism, rather than a mirror, making the measurement even more complicated. The prism does give a correct image, though, which is what you really want in a finder.

So…the tube needs to be cut. This is the most difficult part of the mod, but it isn’t impossible to do. I happen to also have woodworking as a hobby, and have a nice crosscut saw, but any saw that will cut ABS plastic and give you a straight, flat cut will work. The cut will leave a bit of a rough edge, but it can be sanded or filed smooth(er). This edge will not really be seen, so don’t sweat it much. However, the truer the cut and edge you create, the easier it will be to collimate the scope, or to at least assure that it’s close to a parallel light path. Note that I’m avoiding saying this is easy to do. I run into instructions that state something is easy or simple all the time, only to find out that it’s next to impossible to do with the tools I have. But it is a reasonable, not impossible, task.

cutoff point

I came across the place to cut the tube by experimenting. In fact, I have one tube that ended up cut too short, but I think I can give enough instructions so that others will avoid this issue. The tube itself actually gives you the spot to start, so you don’t need to measure anything. There is a baffle inside the tube at the rear. Cutting just one side or the other of this baffle is the spot to start.

Once the tube is cut at this point, the focal length is very close to where it needs to be, in order to bring a diagonal into focus. The cut will look like this, to top half being cut and the bottom half not yet modified.

Note that while doing all this work, remove the objective and keep it protected. Don’t add it back into the tube until you are ready to test the focus.

cutoff illustration

A can of compressed air comes in handy here. You will likely have ABS chips all over the place, and they tend to cling to the tube due to static electricity. Blow everything off as cleanly as possible. If you don’t, you’ll end up with whatever is left clinging to the back side of the objective. I should also note that I use the compressed air to clean dust off the objectives. Yeah, I know you aren’t supposed to do that, but it actually works a lot better than trying to clean the objective with a cloth, and let’s face it – this objective cost all of about $15. I have yet to find any scratches on mine.

Now, you have a shorter tube, but nothing to hold the tail end together, other than the O-rings, and the resulting hole is really too large for the diagonal. You could probably modify the focus tube to somehow hold the diagonal, but I could not come up with a decent solution that I was satisfied with. So I set out to find something that would fit over the newly made end of the scope.

This brings me to the GS3 mod. In searching through the ABS plumbing parts, and believe me, I bought and tried a LOT of different parts, I came across a part that I think is a 2″ to 1.5″ reducer. Note that plumbing parts measure things in several different manners, and like threads, nothing appears consistent. In any case, the part will friction fit over the end of a pipe, and thus the scope, and the other end has a threaded cap and compression ring that just happens to have in ID of 1.25″. The cap will actually tighten around the diagonal barrel quite nicely.

ABS plumbing part mod

The story could end here. I used a GS with this mod for quite some time, but there are a few issues with it, and that is what set me out to find something better. First, the focal length just barely works. I could just get it to focus, most of the time, while wearing my glasses, but not without them. Matt didn’t have any issue, though he was wearing glasses also. I probably could have cut just a bit more off the tube to give more in-focus, but only if the plumbing part would actually push on further and wasn’t at it’s limit. The tube is sloped at this point, so the more you cut off, the larger the OD. It was an iffy situation that would have rendered the scope unusable if the cut didn’t work. Also, over time, the force fit became loose and I was always having to force the end back on, sometimes in the middle of a viewing session. And, one thing that I had not considered was that the scope was poorly collimated. I verified this with a refractor collimator and I wasn’t getting near the views that I should have been getting.

2-inch adapter mod

Off to experimenting again. The breaking point was when I realized that a 2″ EP holder could be fitted over the end. This also fit more deeply onto the tube, making the cut off point more forgiving.

Now I just had to figure out what to fit onto the 2″ EP holder and make it short enough to bring the scope to focus. I started out with a 2″ extender that just happened to have a barrel that screwed off and had a 48mm thread. This is the same thread as a 2″ filter. Note that a 2″ to 1.25″ adapter usually has a filter thread on the bottom, and thus the two could be mated.

2-inch to 1-25-inch adapters

Alas, this solution was just a bit too long. However, your mileage may vary, so feel free to experiment with parts you have on hand before buying any new parts. Actually, with the lowest profile adapter that I could find, I could barely get the scope to focus, but with no leeway, so I kept looking for another solution.

In my searching, I found three different ways to mate a 2″ holder to a 1.25″ holder. There are parts with a 48mm thread, an SCT thread, and a T-thread. Some of these solutions need a Male-Male or Female-Female adapter, depending on what threads the parts have. Experiment with any of these that you might have on hand.

Note that if you can put the 2″ part completely on the scope tube, you can either mark it with a pencil, or just turn it around the tube a few times. You may not be able to get the 2″ part on all the way, in which case you’ll need to estimate how much more of the tube to remove. But, as long as you leave enough room for the 2″ part to grip, you can now cut anywhere between the baffle point and the 2″ mark. I also found that the closer you can come to the inside limit of the 2″ tube, the easier it is to keep the part square as you fasten it down. Having a 2″ part with a compression ring and two or more screws also helps.

There is actually a fourth solution, and it’s the one I ended up using for Matt’s scope. A 1.25″ to 2″ adapter will work if you have the right parts. This is an adapter that allows you to use a 2″ EP in a 1.25″ focuser, not the normal 2″ to 1.25″ adapter. My original solution was to thread a spare EP holder onto the scope end of a diagonal. But, I just happened to have this part spare after converting a prism diagonal to use a helical focuser (at one point I was able to obtain a few of the helical focus EP holders as parts, not mounted on a diagonal). You are at the mercy of the threads matching if you go this route. That was the first version. I ended up buying a prism diagonal from ScopeStuff, though, to get a shorter EP holder. This diagonal happened to also take a helical focuser (threads matched) and the scope end had a barrel that was held on via a 1.25″ filter thread. So, on Matt’s final mod, the 1.25″ to 2″ adapter was screwed directly onto the diagonal body, giving the absolute maximum amount of in-focus (minimum focal length). In fact, the focal point, at least with glass on, is about in the middle of the helical focuser, which is ideal. The 2″ mated with a 1.25″ adapter is shown beside it, so that you can see the difference, around 10mm, in the focal length.

GS Matt version

After looking at the measurements of all the parts I came across I think I have a solution that should be fairly cut and dried (note I didn’t say simple or easy). It ends up that the T-thread adapters that Agena Astro covers are the shortest I could find. I think you will still need a M-M or F-F adapter to connect them, but this only adds a mm or two. This along with the Stellarvue diagonal w/helical focuser should put you in business.

update kit

And to answer Matt’s question…..by the time you get a decent way to focus and add a RACI diagonal to an otherwise inexpensive scope, you might as well buy a RACI finder.

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Observing Report: Night of the Refractors redux

November 20, 2013
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From left to right: my TravelScope 70, my C102, David’s C102. When I took this picture, we hadn’t put the finders on the big scopes yet, or gotten my stand-alone GalileoScope set up yet.

This one is a little late: David DeLano and I spent the night of Sunday, November 3, observing at the Salton Sea. This is the belated observing report.

We met up at the visitor center at the headquarters campground. We rendezvoused there a little after 3:00 in the afternoon because we had some things to do before sunset, which because of the time change was coming at 4:50. The visitor center gift shop has a little astronomy section and both of us picked up a copy of the Sky Atlas for Small Telescopes and Binoculars, by Billie and David Chandler–more on that atlas another time. David also picked up a nice plasticized version of the Chandler planisphere.

Chandler Sky Atlas

After that we drove down to my favorite spot at the Sea, which is the south end of the Mecca Beach campground. A couple at another site were loading up as we were pulling in, and the left a few minutes later. After that, we were the only humans at the campsite all night long, except for someone in the late evening who pulled in, turned around, and left, all without stopping.

Our first activity was dinner at a picnic table in the shade. We split the gear and groceries like so: David supplied firewood and snacks, and I brought dinner (Subway sandwiches) and cooked breakfast (pancakes).

IMG_1243

Even as we were eating, the second activity commenced: the exchange of hostages. As far as I can tell, David is a hot rod mechanic who happens to work on small refractors instead of cars; if that strikes you as hyperbole, just read on. Anyway, he’s way more adept at getting refractors to sing than I am, so I had brought him an unfinished Carton 60mm f/15 refractor and a couple of small objectives that I had rescued from otherwise unsalvageable garage sale scopes. To transfer into my care, David had brought a nice Celestron 2-inch star diagonal for my C102, and–most importantly–a GalileoScope that he had built and modded for me.

Galileo is Rocking Out in His Grave

The GalileoScope was created for the International Year of Astronomy in 2009, when it originally sold for $15. That was mostly down to economy of scale; now that sales have cooled, the price is up to about $50. It’s still a lot of telescope for that price. David’s GalileoScope mods have been featured here before.

The stock GalileoScope is a straight-through instrument with an f/10 objective and a push-pull focuser, which you aim by looking along some gunsight-style ridges on top of the OTA. My GS has had its tube chopped to accommodate a Stellarvue 90-degree diagonal with a helical focuser (the #D1026AF unit here, if you want one for yourself), and has a Daisy red-dot finder perched on the forward gunsight.

IMG_1242

Above, my nicely tricked-out GalileoScope. Bottom, David’s insanely modded version–possibly the most attention anyone has ever lavished on a cheap build-it-yourself 50mm refractor.

Lest you get too jealous of my pimped-out GalileoScope, let me describe David’s own GS. He got the aftermarket f/11 objective kit, which lengthens the light path enough to allow the use of a diagonal without chopping the tube. At the back end of the scope, there’s a 2″ Crayford focuser (yes, you read that right) with a 1.25″ adapter. His diagonal also has a helical focuser for fine-tuning; in fact, in use I forgot about the Crayford and used the helical focuser exclusively. At the front end, there’s some kind of fancy RDF, sold by Cabella’s for use by hunters, with the largest eye-lens I’ve ever seen apart from the “boxy” astro-only unit-power finders, the Telrad and the Rigel Quikfinder. A set of nice rings with Delrin-tipped screws completes the instrument, and allows David to mount it coaxially with his larger scopes as possibly the most awesome luxo-finder-slash-second-instrument that I’ve ever encountered (on a small scope; the 9.5-inch refractor mounted on the 12-inch Zeiss in the Griffith Observatory probably takes the cake for larger instruments).

David’s GS really must be seen to be believed. Once on the Dinosaur Mailing List, Mickey Mortimer wrote, “Looks like it’s time to over-technicalize this previously tame post.” I can’t think of David’s GS without those words going through my mind. I wouldn’t be surprised if it is the most extensive hack anyone has done on a GS. It is definitely the most badass.

I should mention that getting both of the GalileoScopes to work as well as they do involved a lot more than just throwing some nice parts on. It required a lot of work and thought and experimentation. Happily, David documented the process and will have a guest post about his adventures in GS-hacking in the not-too-distant future. So stay tuned for that.

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David’s GS mounted on his C102 as the luxury finder to end all luxury finders.

After dinner and the exchange of hostages, it was time to set up scopes. I was rolling with the C102/SV50 combo again. I also set up the TravelScope 70 just to have something different to plink around with. David set up his second tripod for my GS, and put his mod-tastic GS on his own C102, using a third tube ring to support the GS stalk and rings. This makes for an imposing setup. I studied it as intently as an American astronaut getting his first look under the hood of a Soyuz capsule. We used some antennas on a distant mountaintop to get everything aligned, and then almost immediately we were off and running.

Skyward!

Our first target, at 5:30, was Venus. There wasn’t much to see–basically a very bright half-circle–but checking in just feels like the right thing to do.

Next we turned to the Double Cluster and Stock 2 and spent a few enjoyable minutes tracing out the loops and chains of stars in our various instruments. Like last time, I could see the red stars in NGC 884, and if anything they were easier this time since I knew what to look for.

After that we turned south and did a big tour of the Sagittarius/Scutum area, eventually going north into Aquila and then west through Serpens to Ophiuchus. But I’m getting ahead of myself.

We started with the teapot asterism in Sagittarius, and let that guide us to M8, the Lagoon Nebula. Then we hopped up just a bit to M20 (the Trifid Nebula) and the open cluster M21. After that we took a break to hit M13 in Hercules before it sank down into the light dome over Palm Springs. We returned to Sagittarius with globs on the brain and took in M22, which I thought was a serious contender in the field of majestic globs. Then it was up to the M24 star cloud, where we got lost for a few minutes at the sight of literally thousands of stars in our eyes. Somewhere in Seeing in the Dark–and irritatingly I cannot find the passage right now–Timothy Ferris describes a swath of the sky, possibly M24, as a “wonderland of far-flung suns”. Whether he intended it for M24 or not, it’s an apt description.

At the risk of letting my current bout of refractoritis get the best of me, I must say, the view of M24 through the C102 was just breathtaking. Now, I have visited M24 before, many times. It is one of my favorite places in the sky. But I had not taken a good look at it through a decent-sized refractor under dark skies. The contrast was superb: against a jet-black background, the stars were so finely graded by brightness that I noticed rivers and shoals among them that I had never been aware of before, including a current of brighter stars running north-south and paralleling the Milky Way. Truly, this is the backbone of night.

But even in a palace, one can want for variety (or so I’ve heard), so we ventured onward. Past the open cluster M18 we came to the Swan Nebula, M17, very bright and clear and looking just like its namesake. Then farther up we found M16, the Eagle Nebula, its tendrils of glowing gas wrapped around a dense cluster of newborn stars. Then back to M24 to pick up the open clusters M25 and M23, which attend the majestic star cloud like obsequious courtiers. M25 is one of my favorites; it sits at the center of a curving arc of stars that David describes as a spiral, but that to me has always looked like a fishhook, with M25 as the bait.

After working through all of those objects with the scopes, we stopped for a binocular tour. I had along my Nikon Action 10x50s and David was rolling with his Nikon action 10x40s. I found that if I held David’s green laser pointer between two fingers of my right hand and the binoculars, I could aim the laser beam at the center of my field of view. We shared many sights over the course of the evening using this trick. For starters, we revisited all of the Sagittarius clusters and nebulae mentioned above, and picked up the little glob M28 as well.

DeLano 1 chart - wide

The asterism “DeLano 1” next to Mu Aquilae. It is much more obvious than this Stellarium view shows, and looks more like a bright open cluster.

Then we turned north to Scutum and Aquila. Our first stop was M11, the Wild Duck cluster. Then I took a break for bathroom and snacks, and David went crazy finding new things. When I got back to the scope, I had some catching up to do: the open clusters IC 4756 in Serpens, and NGC 6633 and IC  4665 in Ophiuchus. David had also discovered something pretty that was not listed on any of our charts: a small group of bright stars just north of Mu Aquilae. So far I have not found this listed anywhere as a named object; for the heck of it we called it DeLano 1.

DeLano 1 chart 2 - narrow

A closer view of DeLano 1.

Zoom Zoom Zoom

I see that I have not mentioned what I was using for eyepieces. Thanks to the 2″ diagonal I could use my 32mm Astro-Tech Titan, which gives a wider true field than any other eyepiece I own. In the C102 it gives a magnification of 31x and a 2.2-degree true field of view, which was great for framing almost everything we looked at (the Pleiades fit with a little room to spare, even). My only other 2″ or dual-barrel EPs are the 21mm and 13mm Orion Stratus EPs, which I used infrequently Sunday night. When I wanted more power, I put in the 1.25″ adapter and my new toy, the Celestron 8-24mm zoom eyepiece.

My only previous experience with a zoom EP was a Scopetronix 7-21mm, which was pretty stinky. Zoom EPs always have wider apparent fields of view at high magnification and narrower AFOV at low magnification. That is pretty much the opposite of ideal, but physics is physics, and the comparatively narrow apparent field is tolerable as long as it doesn’t get too narrow–below about 40 degrees you feel like you’re looking through a soda straw. Unfortunately, with the Scopetronix zoom, the AFOV started at 40 degrees (at high mag) and ended up somewhere below 30, at which point the image is so small you might as well be looking through the other end of the telescope.

Happily the Celestron 8-24mm zoom has a more generous AFOV. The stated range is 40-60 degrees, and that seems about right to me. What’s not so great? It’s not parfocal across its magnification range (I don’t know how many zoom eyepieces are), so you have to refocus as you change magnification. Also, it’s a little soft at high power. Not egregiously so, but my 8.8mm ES82 is not going to be losing any sleep. On the plus side, it’s decent, convenient, and at a current street price under $55, dirt cheap.

Incidentally, this is the danger of getting a couple of high-end eyepieces: they are so sharp and so clear that when you go back to merely average EPs, the differences are immediately noticeable. It makes you spoiled.

Lyra, Cygnus, Vulpecula, and Sagitta

After I got caught up in Ophiuchus, we turned north, first to Polaris and the “Engagement Ring” asterism, and then to the Lyra/Cygnus/Sagitta area.

Naturally our first stop was Epsilon Lyrae,  the “double double” star, which was cleanly split at 125x with 8-24mm zoom. So if you’re curious about that eyepiece, there’s a point in its favor.

After that we followed my usual J-shaped path through this  region: from the Ring Nebula, M57, on past the fair-to-middlin’ glob M56 to the brilliant, contrastingly-colored double star Albireo. Like a lot of double star observers, I like doubles when they’re not too widely split, and at 31x the 32mm Titan and C102 gave perhaps the best view of Albireo I’ve ever had in a scope. After Albireo, go straight south to find Collinder 399, better known as Brocchi’s Coathanger. Southwest of the Coathanger one comes to the pair of closely-spaced, equally-bright stars that mark the feather end of the constellation Sagitta, the arrow. Halfway along the arrow a zig-zag pattern of stars leads to the faint glob M71. Then proceed along the arrow to the third bright star up from the feathers and hang a right to find M27, the Dumbbell Nebula.

The Dumbbell does a neat trick as either one’s scope or one’s sky conditions improve. From a small scope, or a big one under city lights, it looks like a bow tie. As things get better, the ends of the bow tie sprout extensions to either side, so the nebula starts to look more like an apple core. Finally the area to either side of the apple core starts to fill with nebulosity, so the nebula ends up looking like a football with a bright band–the former bow tie/apple core wrapped around its “waist”.

10-04-2008_DumbellThe football form of the nebula is obvious in most astrophotos of M27. Here’s a nice example by Rogelio Bernal Andreo (DeepSkyColors.com) that shows the different aspects in different colors: white bow tie center, red apple core extensions, blue football wings. I have seen the football before in the XT10, but I had never seen it in a small scope before Sunday night. And, to be clear, the C102 did not show the entire football. But it did definitely show the wisps of nebulosity extending out on either side of the apple core. It’s probably  best to say that M27 was halfway between  the apple core and football forms. It was missing the crisp cut-off at the edge of the football, which the XT10 will show under sufficiently dark skies. But it was still way more than I expected. I am still learning what a 4-inch scope with high contrast can do under dark skies; the answer is, “an awful lot”.

The striking appearance of M27 can in part be chalked up to excellent transparency in the early evening. Another example is that both of us could clearly make out the North American Nebula, NGC 7000, in the binoculars. My best-ever views of the nebula have been with 15×70 bins out at Owl Canyon. I have caught glimpses of it in the 50mm glasses before, but never as good as it was Sunday night. David was getting it clearly in his 40mm bins, which is pretty amazing.

We did another binocular tour in this area, hitting all of the objects listed above as well as M29, M39, the heart-shaped asterism around the bright star Sadr in the heart of Cygnus, and the wide blue/orange binocular double Omicron Cygni. This was about 8:30 PM, four hours into our 9-hour run.

This is pretty much how we proceeded for the rest of the night: pick an area, figure out some of the best and brightest objects therein, and hop our way through them. David was working off the Evening Sky Map and suggesting objects from its lists, and I was working from the PSA and rediscovering some goodies I hadn’t seen in a while. Rather than give an exhaustive list of everything else we saw, I’ll just list some highlights:

NGC 253 and NGC 288 – NGC 253 is the Silver Coin Galaxy. It’s up there with Andromeda (M31), the Whirlpool (M51), the Sombrero (M104), and Bode’s Nebulae (M81 & M82) as one of the best galaxies for northern hemisphere observers. My first view of it was in binoculars from Big Bear Lake, and under those dark mountain skies it looked as good in the 15×70 bins as a lot of galaxies look through a telescope. Mottled details is visible in even small scopes under sufficiently dark skies. While you’re in the area, might as well drop down about one eyepiece field and pick up the globular cluster NGC 288.

NGC 7789 – Here’s one I’d seen before but forgotten about. This is a nice open cluster off the tip of Cassiopeia, sandwiched between two small groups of bright stars. There are a lot of open clusters in Cassiopeia–we did a third binocular tour that encompassed NGC 457, NGC 436, M103, NGC 663, NGC 659, NGC 654, and Cr 463–but NGC 7789 might just be the best, not only for its inherent charm but for the rich surroundings in which it is set.

M37, M36, M38 – This is the famous trio of open clusters in Auriga, which are among the most popular and  most visited objects in the winter sky. The one that impressed us the most Sunday night was M37, the lowest (east-most) one. It is a dense swarm of tiny stars, which David described as “crystals”, and which to me looked like the proverbial scattering of diamonds on black velvet.

M46, M47, M93 – These open clusters in Puppis are also popular winter objects, especially the close pair of M46 and M47. I suspected the planetary nebula NGC 2438 in M46, which I first spotted at the All-Arizona Star Party back in 2010. Since then, I always look for it, and when I do spot it, I wonder how I was able to go  for so long without seeing it.

M76 – This is the Little Dumbbell Nebula in Perseus, and one of just a handful of planetary nebulae in the Messier catalogue (the others are M27, M57, and M97). As its name implies,  the Little Dumbbell is the smallest and probably least impressive of the Messier planetaries, but I’ve always had a fondness for it. Although small, it has a high surface brightness so it’s not hard to spot if you know where to look, and it is not without its charms.

Planetary nebulae illustrate why the Messier catalogue is a two-edged sword. On one hand, the Messier catalogue does include some best-of-class objects in almost every category of DSO; on the other hand, there are numerous objects in other catalogues that outshine (sometimes literally) the less impressive Messiers. For galaxies, you have things like the Silver Coin and NGC 4565 in Coma Berenices; for open clusters, look no farther than the Double Cluster in Perseus and NGC 663 and NGC 7789 in Cassiopeia; for diffuse nebulae, see the Flame Nebula (NGC 2024), the Rosette (NGC 2237), and the Christmas Tree or Cone Nebula (NGC 2264).

But planetary nebulae get especially short shrift; a quick-and-dirty list of impressive non-Messier planetaries in northern skies includes the Cat’s Eye (NGC 6543), the Eskimo (NGC 2392), the Saturn (NGC 7009), the Ghost of Jupiter (NGC 3242), and the Blinking Planetary (NGC  6826). This is not because Messier had anything against planetaries but because his catalogue was discovered rather than assembled post-hoc, and discovery is always a haphazard process. Still, we are not discovering these things for the first time, and with their often high surface brightness and charming array of forms, planetary nebulae are great targets for beginning and city-bound observers.

By 2:00 AM we were winding down, and so were the skies. A cloud mass that had been hovering over Palm Springs started to send forth offspring, and the haze near the horizon was getting worse. A bright star in Leo that I just couldn’t place turned out to be Mars. We had one last look at the Double Cluster and called it a night.

It was one of the most fruitful observing runs I’ve ever had. By my count, we looked at:

  • 49 Messiers
  • 20 NGC, IC, Collinder, etc., objects
  • 4 double stars (counting Epsilon Lyrae only once)
  • 4 asterisms (DeLano 1, the Engagement Ring around Polaris, the Heart around Sadr, and Kemble’s Cascade)
  • 3 planets (Venus, Jupiter, Mars)

So about 80 things in the sky, not counting the numerous shooting stars, which we noted every few minutes all night long. That is by far the most things I’ve seen in one evening when I wasn’t doing a Messier Marathon. But we weren’t rushing or trying to get through a ton of objects, we were just basically out for a spin, and if you cruise around the sky for 9 hours, you are going to end up seeing a lot.

Lessons

I came away from the evening with a couple of firm directions for future observing.

First, I don’t think I logged anything that I hadn’t seen before (DeLano 1 excepted!), but I saw a lot of stuff that I had forgotten about, like NGC 7789. Most of these were things that I had visited in the course of doing one or another Astronomical League observing program. That’s great because those programs have helped me to learn the sky, and they’ve introduced me to a lot of wonderful objects that I hadn’t seen before. But now that I know the sky, I need to go back and re-observe those things and spend a little more time with them. This is especially true of the many beautiful clusters on the Deep Sky Binocular observing list–I am ashamed to say that there are many of those that I still have not visited with a telescope. So even my terra cognita holds some wonderful things waiting to be rediscovered.

Second, I need to go south (in the sky)! Here’s some relevant math: the Salton Sea campgrounds are at about 33 degrees north latitude. That means that Polaris is 33 degrees above the northern horizon, the celestial equator is 57 degrees above the southern horizon, and with no intervening landforms or atmosphere I should be able to see down to -57 degrees declination when I look south. Now, in practice the near-horizon haze makes the last few degrees pretty worthless. But I have seen the globular cluster Omega Centauri with my naked eyes from the Salton Sea. At -47 degrees declination, it never gets more than 10 degrees from the horizon. If it’s naked-eye visible that low under good conditions, then binoculars and telescopes will reveal much more at the same declination, and maybe even a little lower.

In practice, I have explored almost none of that southern expanse. I am used to thinking of the Silver Coin galaxy as a far southern object, but at -25 degrees it culminates a full 32 degrees above the horizon–more than a third of the way to the zenith! Except for sighting Omega Centauri a couple of times, I have not deliberately gone south of about -30 degrees declination (and I’ve only gotten there in the area around the “tail end” of Canis Major), which leaves a LOT of unexplored sky out there. I was fortunate to get to see most of the best of the southern hemisphere sky when I was in Uruguay in 2010 and it was amazing. Much of what I saw there is visible from here, I just haven’t looked. I need to fix that.

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More low-cost solar observing

June 4, 2012

In preparation for the transit of Venus tomorrow, I did a little hacking and tinkering late this afternoon. Although the sun funnel worked well enough for watching the eclipse, as we’ll see below it is not perfect for photographing the sun in any detail. My full-aperture solar filter still hasn’t arrived, but I got to thinking about how to make a safe direct viewing setup.

I recently acquired a Celestron Travel Scope 70, a little 70mm (2.75 inch) f/5.7 achromatic refractor. Like a lot of small refractors, the dust cap for the objective lens has a smaller removable cap in the middle, in case you want to stop down the scope for more pleasant viewing of bright targets like the full moon. The diameter of the small hole in the middle of the big cap is 40mm, so with big cap on but the small cap off, the scope functions as a 40mm f/10.

I don’t have any loose solar film to make a 70mm solar filter or even a 40mm solar filter. But I do have a stack of eclipse glasses, each of which has two 1×1.5 inch eye holes covered with solar film. So I cut one of the eclipse glasses in half, made a round 25mm aperture in a square piece of cardboard, and mounted the eclipse glasses ‘lens’ (solar film still surrounded by two sheets of thin cardboard) and the 25mm aperture stop on the back side of the big dust cap. I didn’t think to take any pictures of the inside of the dust cap to show how it all goes together, but hopefully the general idea is clear enough. With the big dust cap on and the small dust cap off, the scope admits a 25mm beam of fully solar-filtered light to the objective, turning the scope into a 25mm f/16 solar refractor. And because the solar filter is on the inside of the big dust cap and protected by the small dust cap (in front) and the second piece of cardboard with the 25mm aperture stop (behind), I can leave it in all the time. Take the big dust cap off, the scope functions normally. Take only the small one off, I’ve got a 1-inch solar scope.

Two other design decisions to note. First, the finder–and I use the term advisedly–that came with this scope is without doubt the worst finder I have ever seen on a commercial scope from a brand name manufacturer. It looks like a 5×20 straight-through magnifying finder. However, right behind the (single, plastic) objective lens is an aperture stop with only a 1-cm hole in the middle. So in fact it’s a 5×10 finder with a plastic singlet objective. The immense irony is that the scope doesn’t need a finder at all; throw in a 32mm Plossl and you get 12.5x and 4-degree true field of view, so the scope effectively functions as its own superfinder. So I unscrewed both ends of the finder and dumped out all the plastic optics, turning it into a hollow sight tube. Why is this important right now? Because it’s really dumb to leave a magnifying finder on a telescope being used for solar observing; it’s too easy to forget what you’re doing and accidentally looking through the unfiltered finder and cause serious eye damage or blindness. There’s a good reason that every commercial telescope comes with a “don’t point the scope at the sun, dummy” tag or sticker or both. This is not something to mess around with. If you’re going to observe the sun with a telescope, cultivate the same habits of awareness and deliberate action that you would use around loaded firearms and power saws.

Oh, the included 45-degree prism diagonal is also rubbish and the light tripod looks pretty dodgy. Today I used my standard small-scope setup–an AstroTech 90-degree dielectric star diagonal and a Universal Astronomics DwarfStar alt-az head on a Bogen/Manfrotto tripod–and I’ll doubtless do the same in the future.

The other design thing was the sun shield. At first I tried going without but look into a dark eyepiece to catch a filtered (= comparatively dim) view of the filtered sun while unfiltered sunlight was hitting the top of my head and my upper eyelid had me squinting and developing a minor headache almost immediately. The plastic dewshield on this scope pulls right off, so I got a handy piece of cardboard (part of the packaging of a picture frame), cut a hole just big enough to admit the front end of the scope without the dewshield, slid the cardboard sunshield on and used the plastic dew shield (and dust cap with solar filter) to hold it in place. I also cut a second, smaller hole to let light in to my sight tube sun finder.

If you do something similar, make sure that the sun shield can’t get blown off and take the solar filter with it. In my case, the dewshield slides on a long way and grips both the sun shield and telescope tube firmly; a strong enough breeze might upend the whole setup, but it couldn’t blow off just the shield and filter. Again, eye safety is paramount; don’t take any chances.

Okay, so how did it work in practice? Pretty darned well. I had already aligned the sight tube with the telescope, so all I had to do was rotate the sun shield a bit to make sure the second, smaller hole lined up with the sight tube. Then I could point the scope roughly at the sun and pan around until a perfectly round beam of sunlight (projected on my hand) emerged from the sight tube. That always put the sun in the field of view of a 25mm Plossl (16x, 3 degree true field of view). The view of the sun at the eyepiece was reasonably bright–for an astronomical object, not compared to the unfiltered sunlight streaming down all around–and razor-sharp. The sunspots with their umbrae (dark centers) and penumbrae (lighter borders) were striking, like they’d been etched on stained glass.

Happily, the filtered scope yielded nice, even light all over the surface of the sun, no matter where it roamed in the field of the view. My one beef with the sun funnel is that it can be hard to get really good photos because of the inherent granularity of the screen material. Inevitably some part of the projected sun is brighter than another, and if you manage to get the light perfectly centered, it can easily wipe out the sunspots. The best way I’ve found to avoid this flashlight-beam effect is to photograph the sun from a bit to the side, out of the direct path of the projected light (that’s how I got this very sharp photo), but then the sun is out of round–not ideal if you’re hoping to combine images into a composite or movie, or even get a nice, square-on shot of a circular sun.

For example, in the photo above the sunspots on the left are sharp enough–the big one even shows the umbra and penumbra clearly–but the dimmer two on the right are lost in the flashlight glow of the sun lighting up the screen material from behind. And in this view the sun is already way out of round.

Also note that this image is flipped horizontally compared with the image from the refractor. In fact, this image is correctly oriented. Normally Newtonian reflectors show things rotated by 180 degrees, but projecting the image on the screen undoes that and gets everything back to normal. The solar filter on the refractor just cuts down the intensity of the light, it does nothing to reorient the image, so the image at the eyepiece is right side up but, because of the 90-degree mirror, flipped left-to-right.

I didn’t go to all of this trouble just for the transit of Venus. I mean, I happily would have, had the transit been the only game in town. But it’s not–the Astronomical League has a Sunspotters observing program, and now that I have the gear for solar observing, I might as well start logging. I’ll keep you posted on that.

Now, I should point out that the flashlight-beam effect washing out the sunspots in the sun funnel is mostly a photographic concern. For visual appreciation, even solo, I think the sun funnel still wins. A 4-inch image scale and the ability to put your head and eyes wherever you want–and even wear polarized sunglasses to observe–can’t be beat. But for photography, I prefer the filtered direct view–even in a one-inch scope.

Fortunately I’ll be rolling with both tomorrow. Now if the weather just cooperates…

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Thinking about cheap finders–and cheap finder mounts

March 16, 2012

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

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

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

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

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

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

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

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

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

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

Well, what if I built my own finder stalk?

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

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

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

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

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

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

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

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

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

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Hack that scope

November 8, 2009

A time-honored tradition in amateur astronomy is amateur telescoping making, or ATMing. For many decades, most people didn’t buy their first scope, they built it, sometimes using optics or mirror grinding kits supplied by Edmunds and others, sometimes just hacking with whatever they happened to have lying around.

I’ve messed around with this a little; a couple of years ago I bought a National Geographic brand 76mm reflector at Target at a deep, deep discount. The scope had good mirrors but the mechanics were terrible; in particular, the eyepieces seemed to have been designed by someone who wanted to discourage people from looking skyward. Why, National Geographic, why? The old rule still applies: never buy a telescope anywhere that sells underwear (that includes Toys ‘R Us!). Unless, like me, you only want the scope for its parts, to build it into something better, and you can get it super-cheap.

Anyway, the full saga of the oft-rebuilt 76mm reflector will be a story for another day–not least because I am contemplating rebuilding it for, let’s see, the fourth time.

Outlook

Today I’m writing to bring to your attention this very cool rig built by frequent commenter David DeLano. It’s basically a board with three holes, but this  simple device allows him to mount his GalileoScope (tricked out with a diagonal and helical focuser from StellarVue) and his SkyScout (a handheld computerized planetarium-star pointer-thingy) on the same tripod. And he’s thinking of adding binoculars on top! His inspiration came from this cool tripod adapter from astronomy hacker extraordinaire, Rob Nabholz.

What do you have laying around the house that might make your observing life easier? Give it a think, and if you come up with any cool ideas, let me know!