Sunday, October 11, 2020

 

#568 My Yearly M13: 2020

 

My Yearly M13, like my Christmas Eve peek at M42, is a tradition I’ve maintained through the years—when I can, anyhow. 

“What the heck is Unk goin’ on about now?” One of two astronomical things I’ve tried to do every year, muchachos, is get out and take a picture of Messier 13, the Great Globular in Hercules. Why? Well, it’s tradition. But even moreso, it ensures I’ll have to get behind a camera mounted on a telescope at least once per annum.

Now, I certainly try to and usually do get out and do astrophotography more than once a freaking year. But long stretches do often separate my sessions. The main reason for that being the weather. As I have oft-opined here, it seems to me imaging-worthy skies have been less common over the last 8 years or so than they used to be. I’d be the last to claim you can make any conclusions about weather trends from a mere 8 years of observations, but that is the way it seems to me.

One thing I do know for sure? In the first decade of this new century I had many mid-summer nights of imaging and observing fun down south in Florida at the Chiefland Astronomy Village. That good summer observing began to dry up around 2012, and Chiefland weather the rest of the year began to decline not long after. That is one of the reasons I have not been back to the fabled CAV in nearly five years. Even the still somewhat hardcore (well, a little) Uncle Rod can only stand so many nights holed up in a cotton-picking Quality Inn under cloudy skies. Unfortunately, it ain’t just Florida skies that now seem worse year-round; the same is true up here on the northern Gulf Coast in Possum Swamp.

Be that as it may be. Resolving to shoot M13 once a year, yeah, ensures I get out with a camera and a telescope at least once between late spring and early autumn.  The last time I did some honest-to-God prime focus, long exposure, guided imaging? Wellllll...that was…I can’t exactly remember, y’all, but maybe not since last year's M13.

So it was that once bad old Hurricane Sally had become just an unpleasant memory, and the clouds that had followed in her wake had all flown off, I prepared to shoot my annual portrait of the big glob. Two weeks after the storm, we were enjoying a nice stretch of weather. Plenty of Sun and blue skies with highs in the upper 70s and lows at night in the 50s. While “50s” is a little cool for your aged Unk’s bones, I prefer being a chilled to having the sweat dripping off me and onto the laptop as I try to take deep sky pictures in my bumbling fashion.

So, as October came in, I would be getting out into the backyard with telescope and camera. But which telescope and which camera? As I said last time, I’m lazy in these latter days. What is a pretty much guaranteed way to get recognizable deep sky shots without much effort? Shoot them with a short – medium focal length 80mm APO (color free) refractor. My beloved 80mm William Optic Fluorite f/7.5, “Veronica Lodge,” would fill that bill.

Veronica is elegantly and sturdily built, but still light enough not to challenge my Celestron Advanced VX GEM mount, so that was what I would put her on. The only question in that regard? “Guided or unguided”? The sky Friday before last was clear, but man was it hazy. Haze scatters light, making the light pollution of my suburban backyard worse than it is on a clear and dry evening. That meant I’d probably limit my exposures to two minutes. Since I’d be doing a precise polar alignment, I probably could have gotten away with no guiding at all for 120-second shots. But since I’d have the guide camera with me to do a Sharpcap polar alignment, why not guide?

Scope, check. Mount, check. Camera? I thought that would be my old Canon Rebel. It’s dependable, I have an AC power supply for it, and as things are reckoned today, the 12-year-old camera has relatively large pixels. That ain’t a bad thing in the deep sky imaging game, campers, since “larger pixels” naturally means “more sensitive.”

All that remained was to decide on the software I’d be using.   As always, I’d be controlling the Canon and acquiring images with Nebulosity. The program, by Craig Stark, author of the original PHD Guiding, will do anything I need it to do and more including acquiring, stacking, and processing DSLR images. While it was initially intended for use with Canon DSLRs, it also works with many astronomical CCD cameras.

I dunno about you, but when I’m imaging I do not like hanging out at the freaking telescope. I want to sit at the computer and run the show from there. I could have used Celestron’s CPWI program, the successor to NexRemote, which we talked about a couple of weeks back. That would have allowed me to control everything from the laptop including the goto alignment. I don’t have much experience with the program yet, though, and thought it best to keep things a mite simpler.

The new Cartes du Ciel beta.

Likely I’d be fussing with the other software, trying to remember what little I ever knew about it. So, instead of CPWI I thought I’d use a nice, friendly, simple planetarium program with an ASCOM driver. ASCOM would give me a little onscreen hand control useful for centering objects in the camera’s frame.

What I’ve used most over the last few years when it comes to PC planetariums is the excellent Stellarium. However, a sentimental favorite, Cartes du Ciel, was, I heard, in a new (beta) version, 4.3. That being the case, I thought I’d give the latest CdC a whirl. I’ve noted quite a bit of traffic on the program’s mailing list of late, so Cartes is obviously more than just still alive.

Guiding? I ain’t used anything but PHD2 since it came out. And I hadn’t used anything before that but the original PHD Guiding since the dark ages when I was photographing the skies with my old self-guiding SBIG black and white astro-CCD. It would be PHD2 Guiding all the way. I had to get it going on a new laptop about a year ago, and was quite not sure I had all the settings correct—I hadn’t used it since then—but I figgered it wouldn’t much matter with short focal length Veronica.

Anything else? Well, I was darned sure glad I checked out Sharpcap the day before my M13 expedition to make sure all was well with it. It turned out my subscription had expired. You see, I use the Pro version (the one with the polar alignment tool). It ain’t freeware, being offered on a yearly subscription basis. Seemed like I had just renewed the program for the very reasonable fee of 15 dollars a year, but, yes, another year had flown by. Anyhoo, it took but a few minutes to get a new subscription and a license in place. Glad I wasn’t blindsided by that in the dark backyard, though.

So, into that backyard I went, setting up in my usual fashion with the scope beside the deck and me and the laptop on the deck. It’s like an observatory for somebody who doesn’t want an observatory: I can leave the telescope set up in my secure backyard for as long as the weather stays nice. Sitting at the patio table under a big umbrella, I’m out of the dew and so is the PC. And I’m just steps from my den where I spend my time while the exposures are clicking off. Oh, I check things once in a while, but watching The Mandalorian on TV while drinking a…uh… “sarsaparilla” is a lot more fun than watching the PHD2 guide graph, friends.

While I hadn’t used Veronica in a long while, she went together smoothly:  plunked her into the mount’s Vixen saddle, attached her tube extension to the focuser, put my (excellent) Hotech field flattener into that, and mounted the camera via a, natch, Canon format T-ring.

Nebulosity doing its thing.
Of course, that was only the beginning. The Orion 50mm guide scope had to be secured in Veronica’s finder shoe, the QHY guide-cam had to go into that, and a USB cable and an ST-4 cable had to be hooked up. Had to have dew heaters on both telescope objective and guide scope objective even in the autumn down here in the Swamp. They had to be connected to the DewBuster controller, and it had to be hooked to a power supply. Gotta rustle up the StarSense hand control and StarSense camera. Oh, need an AC power supply for the mount, and—well, y’all get the idea; even setting up “just” an 80mm refractor for imaging is a complex and rather lengthy task.

Whoooeee. I was close to sweating even in the cooling air as the stars winked on. Next order of bidness was polar alignment. I temporarily placed the laptop on a little tray-table next to the scope, plugged the guide scope into the computer’s USB port, and fired up Sharpcap.

How long does a Sharpcap polar alignment take? Maybe 10 minutes first time out. Five minutes or less after that. The process is simple. Set the mount in home position pointing north in declination with the counterweight down. Click in the Tools menu to start the polar alignment.

Sharpcap will expose a few frames and will shortly tell you to rotate 90 degrees in RA. That done, you’ll use the mount’s altitude and azimuth controls to point at the North Celestial pole with the aid of onscreen graphics and text directions (“Move up 12’…”). How accurate is it? Now that it takes refraction into account, I have faith that when it tells me I’m just seconds from the pole that’s just where I am. And my results indicate it is telling the truth. If you have a guide camera, Sharpcap is the obvious cure for the polar alignment blues.

Polar alignment done (the somewhat course altitude/azimuth controls on the AVX make the process more difficult on that mount than on my Losmandy—but it’s not bad), it was time to essay a goto alignment via the StarSense auto-align camera. I’ve never had a problem with the StarSense; it’s always produced an alignment as good as what I can do with the normal hand control. But there are a couple of gotchas to watch out for—one of which your hapless raconteur encountered on this very evening.

Full sized image.
The StarSense camera is furnished with two mounting brackets. One for Synta-style finder shoes and one for the peculiar and proprietary finder mounts Celestron uses on its Edge scopes (and maybe others these days). I’d last used the StarSense on my Edge, so I’d have to unbolt the camera from the Edge bracket and put it on the Synta mount on Veronica. I knew changing mounts would probably affect the camera’s aim and calibration and the accuracy of the goto alignment. But given the wide field of the 80mm, I hoped I could squeak by.

‘Twas not to be muchachos. The StarSense did the goto alignment successfully as always, going to four star-fields and plate solving. When it was done, I sent the mount to Vega, which I thought would be a good target for rough focusing. Fired up Nebulosity, started clicking off focus frames and…no Vega did I see. Tried slewing around a little. Nope. No Vega. Sighted along the tube and did some more slewing. Nope, sorry, Charlie.

There was nothing for it. I’d just have to calibrate the StarSense. That is easy if you, unlike your silly Uncle, remember how to do that. Send the mount to a bright star (Vega in my case). Get the star in the field of an eyepiece or camera (I did that by replacing the StarSense with a red dot finder temporarily). Press Align, and use the hand control’s direction buttons to precisely center the star.

That sounds easy. And it is easy if you, unlike Rod, remember to press Align, not Enter. Pressing Enter sent the mount back to where it was in the beginning; where it thought the star oughta be. So, Unk got to start all over from the beginning after biting the bullet and digging out the StarSense manual.

Got ‘er done, and all should have been well. But wouldn’t you know it? Uncle Rod did some assuming, and you know what they say about that word. Once the calibration is done, the HC tells you you need to do another alignment. That’s easy, just press enter and it will be executed automatically. Silly old Rod, however, thought he should set the mount back to home position first—which you do not need to do. You will not be surprised to learn the AVX pointed the scope to the Earth for the first plate solve. Power down, start over from scratch one more time.

Zoomed in with a crop.
Well, alrighty then. All was finally well. Completed the goto re-alignment, requested Vega, and it appeared in the frame of the camera. I focused until it was as small as I could get it, and then attained fine focus using Nebulosity’s focus utility, which has you use an unsaturated, dimmer field star, adjusting until its displayed HFR (Half Flux Radius) number is as small as you can get it.

OK! We was rollin’ now. That’s what Unk thought, anyhow, but the gremlins weren’t quite done with his sorry self. Time to engage Cartes du Ciel. Started the program, connected the ASCOM driver to the mount, clicked M13, and then the slew button, and off we went for the globular. The mount was about halfway there when the computer went fitified with a blue screen of death. I don’t know I’ve ever had that happen with Windows 10, but it sure did happen on this evening.

Luckily, the mount continued to M13 unaffected, I restarted the computer, reconnected all the software, and the laptop was OK from then on. What was the problem? Despite the fact that I was using a beta version of Cartes, I’m guessing the culprit was actually the older ASCOM version I was running, 6.1. By the light of day, I investigated and found some people had had problems with that one. So, I updated to the current v6.5, even though I had had no further problems with Cartes for the remainder of the evening.

Cartes du Ciel? Other than that hiccup, it was wonderful. No, it does not have the pretty sky of Stellarium, but it makes up for that with the legibility of its display in the field, and has many more features for observers than Stellarium, despite me loving that program very much. Go out and get the new CdC; it is another winning version in a long string of winning versions.

The rest of the evening was frankly pedestrian in the extreme. I got PHD2 Guiding doing its thing without a hitch. While the seeing, never good, was degrading as time went by, my errors were just a little worse than 1” with PPEC not turned on. Well, till M13 began to get lower on the horizon after about an hour, and I began to approach 2”. Unfortunately, in October there ain’t much time before the glob begins to get low; especially if, like your fumbling Uncle, you waste at least half an hour before taking your first sub-frame. But the higher guide error toward the end of my sequence was not a problem. Again, an 80mm scope is very forgiving. You almost have to work not to get round stars.

And...the clouds are back.
A sufficient, I thought, number of 120-second sub-frames in the can, I threw that accursed big switch. The bugs were beginning to bite, the humidity was spiking, the Roku was calling, and so was that sarsaparilla. Not a bad night once I got on track, I thought.

The denouement? Early Saturday evening, I shot a series of T-shirt flats using the sky at dusk as illumination. As I was doing so, I witnessed the darned old clouds begin to flow back in after giving me almost a week’s respite. Not just that...another big storm was shortly threatening the Gulf. So, I was glad I’d got out, full Moon or no (did I mention shortly after my imaging sequence began, a fat Moon began to rise in the east?).  That done, I went through the usual processing steps with Neb:  debayer both lights and flats. Stack lights and flats into single images and combine master flat and master light into one photo, process using Nebulosity, and do final touchup with Photoshop.

“But what about darks, Unk? You gotta shoot darks, doncha?” I did, Skeezix, but I did that as I was shooting the lights, automatically. I set the Canon Rebel to subtract a dark after every image. It takes twice as long to get through your sequence, but I find doing it that way yields better results.  With an uncooled camera like a DSLR, it’s always best to shoot a dark immediately after the light so the sensor is at a similar temperature.

My results? Not so bad. While something like this would never appear in the magazine’s Gallery section (!), I’ve done worse on a hazy night in the suburbs with big Moon rising. Frankly, this year’s shot is at least as good as what I got in 2019 with an LX85 mount and a Meade 8-inch ACF under similar conditions (in late 2019; the blog article didn't appear till January 2020). But you know what? This exercise ain't about results, anyway; it’s about Unk getting his silly old self out under the night sky with a camera and getting back to work, muchachos.


Comments: Post a Comment



<< Home

This page is powered by Blogger. Isn't yours?


stats counter Website Hit Counters