Sunday, October 05, 2014

 

The Refractor Way Part II: Imaging with a Small APO


“’Twas a dark and stormy night.” Not really, muchachos. In fact, the last dark of the Moon Saturday evening was one of the best we've seen in the swamp in a long, long time. Damp, sure, but reasonably cool. Some autumn-like haze on the horizons, but clear 30-degrees up with nice, steady seeing.

As always, though, your old Uncle is putting the doggone cart before the horse. Let’s start at the beginning, shall we? I had several goals for my Saturday night expedition to the Possum Swamp Astronomical Society Dark Site. Firstly, I needed some images, both for a magazine assignment I am working on and for use with my “Uncle Rod’s Messier Album” series here.

I also wanted to do the observing for Part II of “The Refractor Way,” which I began last week. The second installment would concern imaging with a small APO refractor, and, ergo, I needed to do some imaging with a small APO refractor.

Lastly, I wanted to check out a “new” piece of gear, Hotech’s SCA field flattener, which is designed for f/5 to f/8 refractors. While the evening’s scope, the Megrez 80, Veronica, has a moderate f/7 focal ratio and a relatively flat field, she is not perfect in that regard, and I was interested to see what the SCA could do for her. While I received the flattener last fall, the weather, other projects, and our move to the New Manse had prevented me from doing pea-turkey with it.

Come 5 p.m., I loaded up the 4Runner, Miss Van Pelt. Which was not hard to do. I’d only be on site for a few hours, so I didn't need the EZ Up canopy—I’d work out of the back of the 4Runner. Wasn't doing video, so I didn't need a monitor or a DVR. What I packed was the VX GEM mount, the 80mm William Optics Megrez II refractor, “Veronica,” in her case, the Canon 60D DSLR, the Toshiba laptop (for Nebulosity), couple of gear cases, and three jumpstart batteries. One for the DewBuster, one for the mount, and one for the big-screen laptop (via an inverter).

Out at the site, everything was “go” for once. I’d have several buddies with me for the evening, including my old pal Max, who’d be imaging with his 80mm refractor, a Brandon. Most importantly, perhaps, the sky was holding. A couple of my weather resources, including Scope Nights and the dadgum Clear Sky Clock, had been showing a possibility of clouds, but as sunset came on, the few white fluffy things that had been cruising the sky scurried off. Next on your old Uncle’s agenda was setup.

Which was remarkably easy. Plunk down tripod, attach VX mount head and counterweight, place Veronica in the saddle, plug in HC (being careful to get the cord in the right socket less I let the cotton-picking smoke out), hook up battery, rig the DewBuster heater and its battery, install the Intes 2-inch diagonal and reticle eyepiece for alignment, and I was ready to go.

I’d already tested the mount with the Canon 60D and SCA on the scope, so I knew where the declination counterweight needed to go for proper balance (slightly east heavy). Almost all the way up the counterweight shaft, that is. While the Megrez is not a lightweight for an 80mm refractor, she is considerably lighter than the Edge 800. When I get a few pennies saved up, I need to order a 7.5 pound counterweight, which will be more suitable for Veronica and much more suitable for my 66mm APO than the VX’s stock 11-pound weight.

And that was it. No guidescope, no guide camera. Given my experience with unguided imaging with the VX Down Chiefland Way last summer , I was purty sure keeping exposures to a minute or less would, with a reasonable polar alignment, produce round stars with the Megrez's 560mm of focal length. At any rate, I didn’t have a mount for my 50mm Orion mini-guidescope appropriate for Veronica (since rectified), so I’d have to go unguided.

While I normally run the VX with NexRemote, I demurred on this night. I wanted the gear loadout and the cables and the hookup to be as simple and quick as possible. I’d just use the Plus HC that came with the mount. While I still don’t like the new HC as much as I liked the old NexStar hand control, I reckon I’ve made friends with it. I have a perfectly good old-style programmable HC I could use with the VX, but I haven’t yet been moved to do so.

The Hotech SCA Flattener...
Anyhoo, all that remained was to wait for Polaris to wink on. When the North Star did so, I centered him in the hollow polar bore of the VX to make AllStar a little quicker. The closer you get to the pole initially, the less you have to move the mount during the hand control's AllStar polar alignment procedure, and the less the need for a redo of the goto alignment afterwards. I sometimes use a polar align helper program, usually one on my iPhone (the free Scope Help these days) to get the R.A. axis as close as possible to the NCP during rough alignment, but I didn’t this time; just centered Polaris is the polar-scope-less R.A. axis bore.

Now, just a little more waiting to give the alignment stars time to peep out. I spent that time admiring Max's Brandon refractor. While it’s an older scope now and could use some updating, like with a modern focuser, it is still a nice telescope. It's not an APO, but its images show little color. The most striking difference between it and the Megrez? The Brandon looks like an 80mm. Sly Veronica often fools folks into thinking she is a 4-inch. At any rate, the images of deep sky objects the two scopes produce are near identical.

The six-star (two alignment stars and four “calibration” stars) goto alignment went smooth as silk, but it really wouldn't be an Uncle Rod observing run if there weren't some kind of a foul-up, now would it? That came during the AllStar polar alignment. The best star to use for the automated polar alignment routine is one due south, not too far from the intersection of the Celestial Equator and Local Meridian. What was over that-a-way? Sagittarius, and I knew one of the Archer’s stars, Nunki, was in the hand control’s “named star” database, so I thought I’d use it as my polar alignment “tool.”

I mashed the buttons to send the mount to Nunki, and when the VX stopped, I peered into the 12mm reticle eyepiece in Miss Veronica’s diagonal. I didn’t look through the Mergrez’s zero power finder, since I had little doubt the star would be in the field of the main eyepiece. Sure enough, Nunki was just off center and shining bright.

Star visible in the eyepiece, I didn't center it; instead, I hit the Align button on the HC and started AllStar from that button’s menu. First thing that happens is that the HC tells you to center the star with the hand control buttons. I did, and the HC reported that it was synced to the star, Nunki. It then slewed away and instructed me to re-center the star with the hand control buttons. I did so, and the mount slewed away one last time. A considerable distance, since the star was no longer in the eyepiece. The HC’s next message told me to center the star one last time using the altitude and azimuth adjusters on the mount, not the buttons. Hokay…

Zhumell's "Deep Sky" clone...
So far, so good, till I squinted through the finder. The little bull’s-eye was a long ways from Nunki. I was no doubt a degree or two off the pole, but not what looked to be close to five degrees. I was flummoxed. Should I power down the mount and start over? Then I had an embarrassing epiphany. I had it in my head that Nunki was the “top” star on the lid of the teapot. Was that right? I asked Bubba Taras. He had the same impression, but said maybe we ought to take a look at a chart and fetched his Sky and Telescope Pocket Sky Atlas.

Wheeew! Turned out we was both wrong. Nunki is the brightest star in the teapot’s handle. That being the case, the mount had stopped a reasonable distance from the star. I used the altitude and azimuth adjusters to move the relatively small distance to re-center Nunki and we was done.

As I said up above, if you have to move the mount far during polar alignment, you will need to do a new goto alignment (or replace the alignment stars in the hand control). I essayed a goto to M13 to see how we had fared in that regard. The Great Glob wasn’t quite centered, but it was easily in the somewhat narrow field of the 12mm Meade reticle eyepiece. I decided we could get by without messing with the goto alignment, and spent a couple of minutes just admiring the globular.  It wasn’t yet dark, but inserting the 7mm Uwan eyepiece showed good resolution.

It was now camera time. I stowed the diagonal and eyepiece and got the Canon 60D out of my gadget bag. I replaced the 60D’s lens with the combination of a T-adapter ring and the T-threaded SCA flattener, which screws right onto the T-ring. I inserted the whole shebang into the 2-inch extension tube on the Megrez (which is needed for imaging and visual use both). The SCA is particularly cool in this regard. After I inserted it in the extension tube, I turned the SCA's threaded ring, which causes a series of rubber o-like rings to expand, ensuring the flattener is held securely in the drawtube. The nature of this arrangement makes the SCA self-centering, which is critical for good performance.

All that remained of camera setup was connecting the 60D to the laptop via a USB cable and lighting off my camera control program, Nebulosity. When I was done, I was feeling a mite skittish, however. I wasn’t sure whether I’d got the scope properly configured with extension tube, SCA, and T-ring so I could achieve focus. I sent the VX to bright Arcturus and started up Nebulosity to find out.

M13 (click for larger image)...
Two things I really like about my setup are the 60D’s Live View feature and Nebulosity’s focus tools. I told y’all all about Neb not long back, so here I’ll just say its focus mode is finer than split frog hair. Mash the “frame and focus” button and Neb displays the field on the big screen of the laptop with images updating in video fashion. That makes it simple to get a bright star as small as possible. And I was able to get Arcturus nice and small. I had to rack the focuser out a ways, but there was sufficient travel.

Rough focus done, I engaged “Fine Focus” and clicked on a dimmer, unsaturated star onscreen. That brings up a small zoomed-in image of the star along with intensity and Half Flux Radius numbers. Make the first number as large as possible and the second as small as possible, and you are focused.

To make sure everything was copacetic, I thought I’d start with a bright target, M13, natch. Slewed back to the globular, engaged Frame and Focus again, this time with 2-second exposures, centered the cluster up a little, and was soon ready to shoot.

I chose to image at ISO 6400. Some folks look askance at DSLRs’ higher ISOs, but my experience is that you capture more detail, especially in less than perfect skies, with higher speeds, and that today’s cameras are remarkably noise free at bigger ISOs. In fact, sometimes DSLRs' higher speeds offer better resolution than lower ones.

I did a 30-second preview, and was pleased with the results. M13 was a mite small, but not too small. At f/7 with the 80mm, we was only at 560mm, considerably shorter than my accustomed 1400 mm with the Edge 800 at f/7. The stars looked excellent to the very frame edge thanks to the Hotech flattener. I probably don’t have it quite at the correct spacing, but the results were still mucho better than without. I will hunt around and see if I can find a short extension ring before the next run to put the camera a little closer to optimum spacing with the flattener. In short, I was thrilled with the Hotech.

M92
Time to get started, beginning with M13. From the look of the preview frame, it seemed to me 30-second subframes would get it, so I instructed Nebulosity to take 15 of ‘em with the Canon 60D. I hit the “go” button, and wandered off to see what my mates were up to. Since I’d told the camera to take internal dark frames (with an uncooled camera, it is good to take your darks immediately after the lights), completing the sequence would require 15-minutes rather than 7.5-minutes.

What was going on with The Bubbas? What was going on was M57. It looked so good in good buddy Ken's 10-inch Orion/Synta goto Dob—I thought I almost glimpsed the central star at high power—that I asked Taras if he'd send his 15-incher over that  way.

At first, the elusive central star was no-joy, even at 450x, but, suddenly, as I stared, that pesky star winked in. I couldn’t hold it, but at powers from about 450x to 500x, it would make an occasional appearance. Averted imagination? For once, I don’t think so. Max and Taras also saw it. Which is damned good. While I’ve spotted it with my 12.5-inch a time or two, it is often invisible in a 25-inch. What helped? The clear skies were good, but I suspect the main things were that the Ring was close to zenith and that the steady seeing allowed the image to sit rock solid in the eyepiece. At 500x.

Just as I finished looking at M57, Nebulosity played the little fanfare that means, “Sequence is done, Boudreaux.” The last subframe on the screen looked good. The histogram indicated sufficient exposure. And it was easy to see the nearby small galaxy, NGC 6207, even in an unprocessed shot. So, I felt moved to go onto a new target, nearby M92.

M92’s fame, other than its status as a Messier, mostly has to do with it being Hercules’ “also ran” glob due to the nearness of stupendous M13. It was even smaller at 560mm than M13, but looked good nevertheless. I let M92 have 15-more frames at 30-seconds. I paid more attention to the subs as they came in this time, and noted the stars looked good and round and small in all of ‘em. Looked like we was on a roll, y’all.

M8
After M92, I skedaddled over to M10, which was getting right low in the west. I probably should have done M12, too, but by the time I was done, 15-minutes later, it was maybe a little too close to the horizon murk to get started on.

With the whole of Sagittarius laid out before me, I had my choice of legendary nebulae and star clusters. I went for what is probably the best of the best, M8, the Lagoon Nebula. Not only did I need a picture of it for the Messier Album series, I wanted to see how the unmodified 60D would do with nebulae. A thirty-second preview showed substantial nebulosity and even some red color, so I thought we’d give it a go. 15 more 30-seconders.

Before I started the sequence, however, I removed the camera and SCA, screwed a mild light pollution filter onto the flattener, which is, hep-fully, threaded for 2-inch filters, and refocused. I’ve had good luck with my 1.25-inch Orion imaging filter, and I thought a mild Deep Sky-like filter would help with M8, which was a little low and almost into the horizon glow.

While I’ve had success with the Orion imaging filter, I didn’t go out and buy the 2-inch version. No sir buddy. Orion’s 2-inch SkyGlow imaging filter is 130 freaking smackers, and your stingy old Unk wasn’t ready to dish out that kind of moola for a relatively small amount of contrast improvement. I hunted around and found what I wanted at, of all places, Hayneedle.com.

They had a Zhumell (Chinese) 2-inch filter just like I was looking for for about 30 bucks. Guess what? Based on visual looks and the improvement in my images, its performance seems every bit as good as that of the 100 buck more expensive Orion. It’s ain’t fancy; the “Urban Sky Filter” filter don’t come with a data sheet outlining its bandpass. You get a nice looking 2-inch filter in a cardboard box labeled, yes, “filter,” a padded plastic case, and that is it. But it works, y’all. Hell of a buy in this old boy’s opinion.

M22
How did the DSLR do with the Lagoon? My finished images show plenty of red nebulosity. Maybe  tetch less than the astro-oriented 60Da, but despite what you might have been told, the difference is not like night and day. When it comes to nebulae, images from an unmodified Canon require slightly more care in processing to bring out the reds, but not much more, campers.

Like M8, M10, M92, and M13, the target that followed the Lagoon, M22, was another easy and spectacular one. But for its location, which is purty far south, which makes it a little less lustrous from mid Northern climes, this huge Sagittarius globular would walk all over M13. For me down here at 30 north, it is well on the way to doing just that. I could see from the subs that my images of M22 and its rich field would turn out right nice.

With the easy done and the night growing older, it was time to essay a couple of harduns. At the top of that list was NGC 6888, the Crescent Nebula in Cygnus, which can be a tough target (visually) for a 12-inch. I did a 30-second preview, and, at first, it looked like I hadn’t got nuttin’ honey. Peering more closely at the sub, however, showed the dim arc of nebulosity blown off by a misbehaving Wolf-Rayet star. While it was visible in a single 30-second shot, I thought I’d better kick the exposure up to 1-minute. Given the tracking I’d been having all night, looked like the VX would have no trouble delivering round stars with 1-minute unguided exposures.

And, indeed, it did not. The stars looked good in the subs, and the Crescent was “there” enough to make me believe it would look right nice after some processing. Which it did once I ran the final stacked image through Photoshop. I intend to go after it with Veronica again with longer guided shots in hopes of picking up more of the nebulosity between the horns of the Crescent, but I was pleased at my first crack at it with the Megrez.

NGC 6888, the Crescent...
When half an hour of exposures of the Crescent Nebula was finished, it was getting late and damp. Very damp. I had to dry the Megrez’s objective with Max’s dew zapper gun. While I had a 3-inch dew heater strip on the refractor, the 3-inch one was not large enough to go all the way around the scope’s over-sized tube, and the objective eventually gave way to the damp. Next time I’ll make better provisions.

Time for one last shot, I reckoned. I’d wanted to get a picture of Comet Jaques, but had heretofore been stymied by weather. While, given the way it looked in Taras’ Dob earlier in the evening, it was a mere shadow of its former self, it seemed worth a try with Veronica. In my finished images, it’s a little green fuzzball adjacent to a field star. If you hold your mouth just right, you can even see a small tail.

And that was that. Fun is fun, but done is done. With my small scope and relatively light load of support gear, I was packed up and ready to go in a surprisingly short time. By 12:30, Miss Van Pelt and me was rolling for the New Manse. Back there, it was a little cable TV (A Haunting) and a couple of Kolorado Kool-aids. What? No Yell? Nope. I was just too tuckered to enjoy the magic elixir.

Takeaways, muchachos? I was pleased with the evening’s images. They were decently exposed, easy enough to process, and showed mucho cool stuff. It’s remarkable how deep a silly little refractor will go. Maybe even more remarkable is how much easier it is to get pictures when your focal length is short and your mirror don’t have to move to focus. Once I was set up, I just started clicking off deep sky image after deep sky image like a crazed 1960s tourist. What’s next for Veronica? I’ve adapted a guide scope mount for her, and hope to try some longer exposures when I get good weather again. When that happens, be assured you-all will hear all about it.

Next Time: The IBM GEM...

Comments:
Great info, I look forward to all your posts!
 
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