Sunday, December 04, 2016

 

Issue #520: After the SCT Redux


Four years ago, an article appeared here with the title “After the SCT.” In truth, it really didn’t have a darned thing to do with Schmidt Cassegrain telescopes. What it was was a report on the 2012 Deep South Regional Star Gaze. That year, the telescope I took to the event was my hallowed 12-inch truss tube Dobsonian, Old Betsy. The fact that I had her on the field instead of a Schmidt Cassegrain impelled one of my (shocked) fellow star partiers to ask me worriedly whether my next book would be called After the SCT. I replied, “There ain’t no ‘after’ for [me]. I am still Mr. SCT and I still use Schmidt Cassegrains more than any other design of telescope.”

Yes, despite leaving the CATs at home with the cats in 2012, it was true I still loved SCTs best. Well, maybe that was true, or maybe I was whistling past the graveyard. Those words were written just after I completed the observing project of a lifetime, The Herschel Project, my quest to view all 2500 Herschel deep sky objects. Chasing down more than two thousand galaxies, nebulae, and star clusters over the course of a mere three years, especially given our weather and my work schedule at the time, ensured I was sorta wrung out and ready for a change.

Oh, I continued on for the next two years much as I had, using my SCTs to slowly, ever so slowly, tie the ribbon on the H-project. Using my C11, Big Bertha, and my C8, Celeste, to clean up a few objects here and there. Some that I wasn’t 100% sure I’d identified correctly, and some that I wanted to re-image with my new color Mallincam. That’s what I told myself I was doing anyway, but the truth, I think, was really that I had no idea what—if anything—came next for me in (amateur) astronomy.

I did try to get various new observing projects off the ground. I started in on the ARPs, for example, observing them in much the same way I had the Herschels. Some visual observing with the C11 and the 12-inch Dob and lots of video observing with the C8 and C11. It, like every other project I tried, however, fell flat. With a resounding thud. I was worried. Had finishing the Herschel Project also finished amateur astronomy for me?

There it remained until early 2015. That’s when things began to change. No, I didn’t suddenly think up a new approach to amateur astronomy. That happened, but it was the result of other changes. Mostly me entering in upon a time in life when I began considering larger questions than just “Hmm, I wonder how a C14 would do on a CGEM DX?” The big questions, questions like, “How did I get here?” and “What is it all about?” and “What (if anything) comes after this story is done?”

“Began to change”? Not hardly. The astounding thing was that I went to bed one night in early 2015 (after imaging that winter’s cool little comet) feeling much the same as always, and awakened feeling entirely different. What concerned me now was no longer observing projects, but the questions above and many more like them, which suddenly seemed more significant than Arp galaxies. I also began to look with dismay at all the astro-junk I’d accumulated over the last 25 years of my near 50 years as an amateur and began to thin the herd.

Big Eye of my 6-inch...
I won’t bore you with the answers to some (not all) of those questions I’ve come up with so far. Every person has to wrestle with these things for themselves and the answers you arrive at may be starkly different from those I’ve arrived at. We’re talking astronomy here, anyway, and the point is that being preoccupied with deeper thoughts meant I didn’t want to worry about, struggle with, or obsess over telescopes anymore. I did still want to observe, though.

I just didn’t want to be bothered by my telescope when it was time to watch the skies. The C11 was out. So was the C8. I didn’t want to spend 30-minutes setting up a scope. Heck, I didn’t want to spend 2-minutes. In the months immediately following that 2015 winter’s night with the comet, the yen to look at the stars often came on the spur of the moment, and our AR102 4-inch achromat or my C102 4-inch achromat on a light SkyWatcher AZ-4 alt-azimuth mount didn’t bother me. I’d put one of the refractors on the mount and carry it into the backyard in a single piece. No drives, no batteries, no computers, no aggravation, just me contemplating the cosmos.

Yes, I will admit I missed the light gathering power of the SCTs at first. My solution was to buy an inexpensive and ultra-simple 10-inch solid tube Newtonian, a GSO Dobsonian, Zelda. She is almost as quick and painless to set up as the refractors. Do I use her a lot? I did when I first got her, but of late not quite so often despite her simplicity. This past year, my refractors have been in the backyard more often than the big 10-inch. 

What changed? I began concentrating on what I could see with my "small" refractors rather than what I couldn't. When I learned to do that, it was as if the deep sky became new to me again after all these years. I won’t tell you I was seeing more details in my favorite objects, but I was seeing a different, a new—or at least forgotten—aspect of them and I welcomed that.

It wasn’t just my new mindset that impelled me begin a more relaxed sort of visual observing. It was my body. No, age didn’t suddenly catch up with me, or at least that was only part of it. I was washing down the front porch of good, old Chaos Manor South just after we moved out. Stupidly, I was wearing flip-flops, slipped on the soapy front steps, and crunched my back—but good.

I was in pain for a while, but it seemed as if I’d dodged a bullet and just gotten bruised up and that would be the end of it. Guess again, Skeezix. Last summer, it became obvious that was not the case. I did something that aggravated that back injury. I don’t know what it was, but I was in real pain for weeks. Carrying a C8 into the yard would have been laughable. 3-inch and 4-inch refractors became my lifelines to astronomy. And I had so much fun with them that when my back pain suddenly subsided—almost overnight—my inclination was to stick with them.

The C102...
Sure, I could have gotten a similarly light and portable CAT, a C5 or a C6 SCT, or a 4 or 5-inch MCT, and used it in similar grab ‘n go fashion, but the refractors, and especially the AR102, had the additional benefit of giving me wide-field views at my dark site. That's something I seem to favor these days. Maybe just because I am weary of examining tiny bites of the sky, looking at PGC smudges, after the years of the Herschel Project. Or, maybe, thanks to my new philosophical bent, I have come to want to see the big picture. I'd also be lying if I told you I haven’t begun to appreciate a certain refractor je ne sais quois.
  
What is that special something refractors are supposedly imbued with? There is one overriding advantage to them:  they are unobstructed systems. There is no secondary mirror getting in the way of the of the objective lens. That has several benefits.

First, the light gathering power of the scope is not compromised by the blockage of the secondary. You get the full effect of the aperture you’re paying for; it’s not “4-inches minus the secondary mirror.” That helps some, but not really a lot, since the light gathering power of the telescope is dependent on the area, not the diameter of the mirror or objective. Still, more light is always better than less.

A refractor will deliver more light than a reflector of the same aperture not just because of the absence of the light blocking central obstruction, but because a higher percentage of light is transmitted through a lens than can be reflected by a mirror. As the coating of a mirror ages, its reflectivity decreases and a refractor continues to pull ahead, often to the tune of 1 or 2-percent a year.

Somewhat better light gathering power aperture for aperture is not the largest advantage of a lens-scope, though. What is more important is the better contrast offered by them. The lack of that central obstruction results in sharper, higher contrast images. Not only does that help with details on Solar System objects, stars often look better in lens-scopes.

You often hear refractor-philes say stars are “smaller” in a refractor than in a reflector. That is due in part to refractors often being smaller aperture, shorter focal length instruments than the average reflector. But that is not the whole story.

As you probably know, stars are not perfect pinpoints in any telescope. The merciless laws of physics make that impossible. What we see is an “Airy disk” surrounded by diffraction rings. Here’s the thing:  thanks to the missing secondary mirror, refractors distribute less energy into the diffraction rings and more into the Airy disk than obstructed telescopes. Stars tend to look “smaller.” If you’re trying to split double stars at the limit of the telescope’s resolution, the less prominent rings in a refractor may make the difference between success and failure.

Finally, one of the most important advantages of a refractor for me these days is one’s thermal stability. Despite their closed tubes, refractors require considerably less time to cool down than reflecting telescopes. The lens is less affected by changes in/changing temperature than a mirror and is ready to deliver good images more quickly when moved from a warm house to a cold yard. Despite our relatively mild climate, I find my 6-inch refractor is ready to go much sooner than my 5-inch Maksutov Cassegrain.

Zelda...
None of the above is to say reflectors don’t have advantages; they do, of course. They are cheaper per inch of aperture, available in (far) larger apertures, and are more portable in larger sizes. These things are true, all things being equal, but all things are rarely equal.

A 6-inch achromatic refractor is still considerably more expensive than a 6-inch (or 8-inch) reflector, but 6-inch achromats are much more affordable than they have ever been. If you just have to have 12—or 20—inches, you don’t want a refractor, true, but many of us, especially those of us focused on imaging, find we don’t need more than 6-inches of aperture to be happy. Portability? A 6-inch Newtonian is nothing; a 6-inch refractor is something of a beast. Nevertheless, I find setting up my 6-inch on a GEM to be easier than setting up my fork mounted Ultima 8 was in the old days.

There’s also the color question. “False” color, the purple fringing around bright objects in some refractors. This chromatic aberration is not necessarily a deal breaker. APO/ED refractors that show virtually no false color are, like achromats, cheaper than ever. Also, some people are more disturbed by color than others (as we baby-boomers age and our corneas yellow a little, we become ever more happy with “just” achromats). Finally, most of us don’t spend much time observing that bane of achromats, Venus; usually we are viewing deep sky objects that show little or no false color.

The ground truth for me is that the refractor advantages, sharp images, the portability of smaller aperture refractors, and their relative immunity to cool-down issues, have made these telescopes more practical for me for visual use now. Most of the time. There are still times when I just have to drag out my trusty 10-inch Dobsonian. BUT—and I hope I am not turning into a refractor snob—when I look through that Newtonian, something, that ineffable refractor something, is missing.

While I have not done a lot of video imaging since the end of the Herschel Project, that doesn’t mean I haven’t done any astrophotography. Admittedly, I laid off for a while following that night of the comet, but when I eventually picked it up again and began doing some simple, informal deep sky imaging with my DSLRs, I actually found it relaxing. Since I was using refractors for visual work, it seemed a natural to continue with them for photography. And was I ever glad I did.

The best thing about refractors, for me anyway, is their imaging capability. Affordable apochromats may be the best thing to hit amateur astrophotography since the death of film. Let me say here that I have recently been experimenting with imaging with inexpensive achromats, and I’ve been amazed at what they can do, but if you want to do astrophotography, you want an ED scope.

One of the things I'd known for a while, but had filed away in a little drawer in the back of my mind, and only recently taken out (along with some non-astronomy related things) and examined in detail is that deep sky imaging is just easier with a refractor. As you know, I've taken many a shot with SCTs over the years, but my results were never, frankly, quite as good or easy to get as what I can achieve with my 5-inch APO refractor given my modest skills. Sure, if I could afford an AP or Bisque or 10Micron mount I might still be slapping a big CAT on the GEM, but I can't afford a ten-thousand dollar mount these days. Refractors are more usable for imaging on my Ford and Chevy mounts. 

OK, so what makes a refractor better for imaging? Three things, I’ve found, speed, focusing, and weight. By “speed,” I am referring to the telescope’s focal ratio. As you may be aware, what matters when determining how bright an extended object (a galaxy or nebula) will be to your camera and how long your exposure will need to be to adequately record it is the telescope’s f-ratio. F-ratio for f-ratio, the only thing more aperture gets you on extended objects is larger image scale. The typical SCT is at f/10, and that requires punishingly long exposures to properly expose dimmer objects. The average apochromatic refractor, in contrast, comes in at f/5 – f/7. Getting these smaller focal ratios with an SCT will require a focal reducer, which can cause illumination problems, vignetting, among other things.

AR102 + AVX...
The average f/10 8-inch or larger SCT has another liability thanks to it aperture and higher focal ratio:  long focal length, as in 2000mm and longer. If you’ve tried deep sky astrophotography, you know with every increase in focal length, tracking becomes more critical. Your mount will have to offer excellent tracking, and you may have to guide it even during shorter exposures if your pictures are to have round stars. Alas, the mounts most of us can afford are challenged by long focal lengths, and it’s difficult to get untrailed stars even with guiding.

Focusing as done in SCTs, with the usual moving mirror arrangement, is also a problem for imagers. I don’t just mean focus shift, the subject moving in the field as you focus, but, worse, mirror flop. As the scope tracks, changes in attitude can cause an SCT’s mirror to move slightly, producing trailed stars if you are using a guide scope for photographic guiding as most of us do. Some modern SCTs have mirror locks, and some of Meade’s newer scopes have improved focusing systems, but almost all SCTs are still saddled with the old mechanics and resulting flop.

Finally, mounts always track better with lighter payloads. The GEMs most of us turn to, which tend to be in the Atlas/CGEM class and below, may track very well during imaging with an 80 or 100mm refractor onboard, but can have real problems with 8-inch and larger long focal length SCTs.

Certainly you can take good pictures with SCTs; I’ve taken my share over the years. It’s just easier to do, much easier, with a short, fast refractor. If nothing else, astrophotography is less stressful—it can even be fun—with a refractor. I don’t ever remember a time when I was doing long exposure imaging with an SCT that I wasn’t at least slightly stressed out by something.

And there you have it. More than a few of you have stared in open-mouthed amazement at the news your old Uncle has become a refractor man. Believe you me, nobody is more surprised than moi. That’s just another example—in a rather long series—of how wrong I was a few years ago when I just assumed this stage of life would be without surprises.

Don’t be too sad about this if you’re an SCT enthusiast. I haven’t completely deserted your camp. I still have my Edge 800 and my C11 (though I keep telling myself I will sell Bertha, the 11). None of this says all that much about the basic worth of SCTs. They are still the most versatile scopes, period, and I will always love them (I even have plans for a Solar System imaging project for my Edge C8). No, what my current transition to refractors speaks volumes about is me. 

Sunday, November 27, 2016

 

Issue #519: How Simple Can It Get II: Kicking it Up a Notch


You’ve accumulated some hours in the backyard imaging with a simple achromat and an Atlas/Sirius/CG5/LXD75/AVX/Bresser Exos-2 class mount. You’re pretty pleased with the results you’ve gotten, and as your processing skills have advanced, you’ve been known to mutter, “Hmm, not bad, not bad at all” when looking at your latest batch of astro-snaps. You’re beginning to think you might be ready to take astrophotography to that vaunted next level, and your questions now are “Should I?” and “How?”

As for the first question, “Should I?” the answer, as it so often is in astrophotography and amateur astronomy in general, is “It depends.” If you are planning on continuing a program of imaging relatively bright objects from the backyard, a higher quality scope and guided imaging can make some difference. However, as you can see in the shots below, it is not like night and day.

Look at M27. The top picture is our original unguided stack of 20 30-second exposures taken with the AR-102 achromat. On the bottom is a stack of 20 3-minute subs done with my William Optics 80mm Megrez II APO. The APO shot is better, but it sure ain’t like night and day. The colors are somewhat more saturated, there is less noise, there is a little (but not a lot) more detail in the nebulosity, and, the main thing, the bright stars are smaller and have no halos. There is even less difference when comparing the APO/Achro M15 pix. These pictures were taken under marginal conditions, but still represent, in my experience, what you can expect from the backyard when you kick things up that notch.

Could I have made the difference larger by exposing for longer with the APO? Yeah, if I could have done that. In my backyard, especially in the presence of the not uncommon haze and humidity which amplify my light pollution, I can't go any longer than 3-minutes, really. As you can see in the unprocessed frame, the sky background was already extremely bright at a modest 120-seconds. I could have used a mild light pollution reduction filter to tone it down, but that brings its own problems.

Verdict? If you plan on continuing to do almost all your work from your less than perfect backyard, focusing on the more prominent objects, and the look of brighter stars in the achromat shots doesn’t annoy you, stick with that achromatic refractor and short, unguided exposures. If nothing else, completing a major project with a simple setup, maybe like imaging the entire Messier catalog from your back forty, will prepare you to take full advantage of more complex rigs if/when you decide to move up to that next level. Your wallet will certainly thank you for sticking with that humble AR102.

Still, there are reasons to think about upgrading to an apochromatic refractor. There’s no denying an ED APO scope is a more versatile scope. One is, for example, more suitable for viewing the Moon and planets—not that the Moon and planets can’t look good in a 4-inch achromat. The main reason for you to switch to an ED scope, however, is if you want to go deeper and intend to do at least some of your imaging from dark sites.

The longer exposures possible from a better observing location buy a lot. Some time back, I did M33, the Triangulum Galaxy. First night out I was tired and didn't want to stay on the observing field long and, so, stuck to short (2-minute) subframes. Looking at the raw images the next a.m., I determined I needed considerably more data, more exposure, to the tune of 3 – 5 minute subframes to make the galaxy really pop. When you are out in the dark you can do that, expose long enough to bring out faint details without the crazy bright background of backyard shots making that a losing battle.

OK, so if you want to take it to the next step, either because you’re going to start imaging at a dark site or because you just want a telescope that will do more things well than an achromat can, step one is getting an ED refractor. My choices, being cheap as I am, are the Explore Scientific triplets or the SkyWatcher Pro ED doublets. While the three element objectives of the ES scopes should theoretically put them ahead of the game in color correction, it’s really a wash when comparing them to the SkyWatchers. Unlike the ESes, SkyWatcher's two element objectives contain one lens made of FPL-53 synthetic fluorite, which makes up for the lack of a third lens element. Either a SkyWatcher or an ES is a great and economical choice whether you choose 3, 4, or 5-inches of aperture. I own the SkyWatcher Pro ED 120, which is a great scope, but I could be just as happy with the Explore (Triplet Essential) 127.

Achro top, APO bottom...
Get that new scope, have fun seeing what an essentially color free refractor can do, and and when you're ready try some longer exposure imaging with it. What you’ll quickly find is that once you get much the 30-second - 1-minute level, you likely won’t have perfectly round stars with the class of mounts we are using. If you want to go longer, you will need to guide. You’ll need a second camera that monitors the position of a “guide” star and issues corrections to the mount to keep that star centered. To do auto-guiding, you will need three things:  a guide telescope, a guide camera, and software to make it all work.

Guide Camera

Any camera, still or video, capable of sending images to a computer over a USB connection is capable of working as a guide camera. However, for best results you’ll want one that is sensitive and delivers monochrome images. The reason you need sensitivity is clear:  you want to always be able to find a guide star in the field of your target. A star that is good enough in the signal to noise ratio department to allow your guide software to stay locked onto it. The reason to pick a monochrome rather than color camera is that monochrome cams tend to be more sensitive and also less noisy.

So, which one? One of the best guide cameras in the business is Starlight Xpress’ Lodestar. Unfortunately, it’s not just a great guide cam; it’s a fairly expensive one at 650 dollars. At the other end of the price scale is Orion’s StarShoot Autoguider at about 250 bucks. The Orion works—I used one for years—but there is no denying it could be more sensitive. Also, while most guide cams can be used as imaging cameras as well as guiding cameras—many can do a good job on the planets or even the deep sky within reason—Orion’s StarShoot is really for guiding only. It can be made to deliver images with special software, but they are not very good.

So which one? After agonizing over the guide cam question for a long time after I decided to replace my Orion, I settled on a QHY 5L-IIM. It is the same price as the StarShoot (actually, the StarShoot is a rebadged, earlier model QHY camera), but is far more sensitive and is an impressive planetary imager, too. It’s small, it’s cute, and it is oh-so-sensitive. In my years of using the StarShoot, I never landed on a field where there wasn’t a single star I could use for guiding.  Frequently, however, there were only two or three even marginally usable stars in the frame, and seeing them took 3-second or even longer guide camera exposures. The typical QHY 5L-II field is filled with dozens of good guide stars in short exposures.

How long your guide cam needs to expose to deliver a suitable star is important because of the inexpensive mounts we are using. If you are forced to use three second or longer exposures, the mount’s periodic error over those three or more seconds may cause your stars to trail slightly. With the QHY I can always get by with one to 1.5-second guide exposures.

Achro top, APO bottom...
Guide Scope

The guide camera needs a telescope to look through. That can be the imaging telescope if you use a device called an “off-axis-guider,” which diverts a small amount of the light from the main scope to the guide camera. An “OAG” is difficult to use, however, and unless you are attempting to image at focal lengths above about 1300mm, especially with an SCT, it is a tool you’ll want to leave for later. Instead, use a guide scope, a small telescope piggybacked on the main instrument.

That guide scope can be any sort of telescope (excluding a CAT with moving mirror focusing). 80mm achromatic refractors like the Synta Short Tube 80s are often used. The 80 f/5 can indeed work well if it is securely mounted. If it is not securely mounted, if its mounting flexes as the telescope changes attitude, etc., stars will trail no matter how good the auto-guiding. Mount that sucker as sturdily as possible using high quality solutions from Losmandy or ADM. Or, if your imaging scope is less than 1000mm in focal length or so, think about a 50mm finder-guider.

A finder-guider is basically a 50mm finder scope that has been modified to accept a guide camera with a 1.5-inch nose-piece instead of an eyepiece. The advantage to the finder-guiders is that they are light and are securely mounted in the average 50mm finder mount and not likely to flex. With a QHY or similarly sensitive camera, one will pick up plenty of guide stars across a wide field. I have even used one semi-successfully with my 8-inch SCT reduced to f/7.

Software

There are numerous guiding packages available, but what is most everybody using? PHD Guiding. Talking the ins and outs of setting it up and using it is the subject for an entire article, which I did a couple of years ago. I will say, though, that the latest iteration of the program, PHD2, is almost plug and play. You will likely get good, if not necessarily perfect, results just using the defaults. Anyhow, start with PHD2 if for no other reason than that so many people are using it that there are oodles of tutorials on how best to adjust its somewhat bewildering array of settings. 

Hooking Up

Like working with PHD, setting all the gear up for auto-guiding is a subject for an entire article (here). Basically, though, what you will do is mount guide scope and guide camera on the main scope and plug in two cables. Assuming your mount has an auto-guide input, you’ll run the (included with the QHY) RJ type ST-4 guide cable from the RJ plug on the camera to the RJ plug (the auto-guide port) on your mount. Then, connect a suitable USB cable from the camera to the computer. What if your mount (like the LXD75) does not have a guide input? You can still guide using the mount’s serial port. See the above article for details.

Finally, start PHD and begin taking frames with the guide camera. Follow the instructions that came with the guide scope to achieve initial focus. Getting the guide scope in decent focus is critical for good guiding performance. Some gurus will tell you that being just ever so slightly out of focus yields better guiding, but you still need to be close to focus for good results. One tip? Clicking on a star on the PHD video display will give the current signal to noise ratio. Adjust focus on the guide scope until that number is as high as you can get it. When you are done, click on a bright (but not saturated) star, and click the bullseye reticle icon. PHD will then “calibrate,” move your mount in the cardinal directions to get a feel of how it responds, and will begin guiding.

Before processing...
From there? Take pictures just like you did in the 30-second days, only with longer durations, maybe beginning with 1 – 2 minutes. Another tip? As I hinted at last time, use Nebulosity to control your Canon camera. It makes everything so much easier. Be aware that to use longer exposures with Nebulosity and the early Canons like the Rebel Xti, you’ll need to connect a shutter interface box between the camera and the laptop. Those are readily available from Shoestring Astronomy.

Processing

It’s morning. The birds are chirping, the sun is shining, and you are ready to see what those hard won long exposure images look like. Process them the same basic way you did your 30-second shots. Stack them using Nebulosity’s built in stacker or the freeware Deep Sky Stacker. Is there anything you will have to do differently when processing longer exposures? In the backyard, the sky background will be considerably brighter, so you’ll have to deal with that using your processing program’s histogram adjustments. You may also have some light pollution gradients. These are the effects of the bright backyard sky and will cause some areas of the image background to be brighter than others. One typical effect of this is vignetting.

Vignetting is what I call “the porthole effect.” The center of the image is brighter than the edges. It’s like you are looking through a round porthole at your object, and will limit how much you can brighten the target. There are two ways to deal with that, the hard way and the easy way. If you want to go hard, take flat-field frames: illuminated, evenly illuminated, shots of the twilight sky or a white card or through a translucent mask. Apply those flats to your images (with Nebulosity or your astrophoto processing program of choice). Or, if you are lazy like me, you can take the easy way out and use a software tool called Gradient Xterminator.

Gradient Xterminator is a simple plug-in for Adobe Photoshop that will virtually eliminate any light pollution gradients. It is extremely simple to use, and the only real “problem” is that you’ll need Adobe Photoshop to use it (it will also work with some versions of Photoshop Elements). Adobe Photoshop is something you probably want anyway as you grow as an imager, and there are options today for getting it that aren’t quite as painful on the pocketbook as in the past.

In addition to light pollution gradients, the sky background in light polluted areas, especially if there was haze present during the exposure, may be badly discolored, brownish or even red as in the example here. It will be even worse if you, like me on the night I shot these pix, allow a little dew to accumulate on the objective without noticing it (I was inside watching TV while Nebulosity took my pictures). The easiest way to fix this yuckiness is with the background color offset tool in Nebulosity. That turns a pain into a pleasure when it comes to getting the sky the correct hue.

And, well, you know what? That is about it. Going from unguided imaging to auto-guiding is quite a leap, but it is the biggest leap you will encounter in astrophotography. Everything else is incremental improvements:  better mounts, cooled CCD cameras, imaging through filters with a monochrome camera, etc., etc. Once you have mastered setting up for and doing guided photography with your simple rig, you have conquered 90% of the astrophotography learning curve, and can now, I hope, actually start having fun.

Sunday, November 20, 2016

 

Issue #518: How Simple Can It Get?


AR102 and Atlas...
More than a few new amateurs want to take pictures of the night sky. Specifically, they long to take images of deep sky objects, galaxies, nebulae, and star clusters, through the telescope. The time-honored advice given these people is “Start simply. Take star trails photos with your camera on a tripod and move on up to piggyback imaging. Through the telescope? It’s expensive and there is just so much to go wrong. Your backyard isn’t good enough to let you get much of anything anyway. You don’t want to spend all that money and time and have nothing to show for it, do you?”  But is that the correct advice?

I think the first part of the above is valid. Beginning with star trails and then piggybacking the camera, mounting it on the tube of a telescope so it can take advantage of the mount’s tracking while shooting through its own lens, is still the way to go. If nothing else, it gets the novice acquainted with focusing on the sky, operating the camera for long exposure work, and the realities of setting up to do any kind of astrophotography. The rest however? Those cautions about how hard and expensive it is to shoot through the scope and that you can’t do any deep sky work from the average suburban backyard? I set out to prove that wrong just the other night.

Not that I was completely sure I would prove that hoary advice wrong. Especially since my other goal was keeping the cost of gear down just as low as it could possibly be, radically low, and making set up and image acquisition as simple as possible.

First thing any deep sky imager needs is a decent tracking (equatorial) mount. Most of us, however, whether beginning or way advanced, don’t need a 10-thousand-dollar rig. That’s because most of us don’t have the dark and constantly clear skies that justify such an expense. Most of us don’t envisage doing 8-hour LRGB exposures anyway. We just want nice snapshots of the prettier objects to share with our friends and families. If that describes you, you can get a perfectly adequate (used) German equatorial mount (GEM) for 300 – 600 dollars.

What I chose to use for this test was my nine-year-old Synta-made Atlas mount. It is not fancy, but offers decent goto, excellent stability, and (unguided) tracking quality good enough for the relatively short exposures and focal lengths most will want to mess with in the beginning.  A used Atlas (a.k.a. “EQ-6”) can be had for as little as 500 – 800 dollars (for the goto version; avoid the old non-goto variant).

Unfortunately, EQ-6 owners tend to hold onto their mounts, so these GEMs are not as common on the used market as you’d expect given their numbers and the many years they’ve been in production. 500 – 800 might also be a bit much for a novice.

80mm APO on a VX mount...
Another good alternative is a Celestron CG5 goto mount or a Meade LXD-75. These are plentiful used and can be had for 400 dollars or even less. They won’t track quite as well as the Atlas, but they will be good enough for beginners using short, fast (low focal ratio) telescopes, and have the advantage of being much lighter than the Atlas. How about similar non-goto CG5 class mounts? Only resort to one of them if you have no choice. Computerized pointing is a huge help in imaging. Do you really want to spend half your time just getting a target in the frame of your camera?

Now for the telescope. To speak plainly, get a refractor. Yes, I’ve had a long running love affair with Schmidt Cassegrains, but I can think of no more difficult scope with which to begin astrophotography. Even when equipped with focal reducers, their focal lengths are long—meaning tracking is critical and it’s difficult to produce images with round stars—and their moving mirror focusing arrangement is a pain for imaging. That alone can cause trailed stars.

I will admit it is possible to get started using an SCT. I went from fooling around with Newtonians to taking my first successful deep sky photos with an SCT and a film SLR. Course, you really had to want those pictures. You had to focus with a dim SLR viewfinder, guide by hand, and it was never certain whether you got anything until you developed the negatives. It seemed worth the pain to me those long years ago, but even when I was younger and more patient, it wasn't exactly "fun."  

Today, lazy and ornery as I am (my friends have taken to referring to me as The Honey Badger), my least favorite thing in the world is taking long exposure pictures with an SCT. Get a refractor. Specifically, an 80mm to 100mm refractor with a focal ratio of f/5 to f/7 or a bit more. Of late, my 80mm refractor has become my most oft used telescope for imaging.

But exactly what sort of refractor? In order to keep the price of the telescope down, naturally you’ll be buying a Chinese scope. Possibly a used one. What would be ideal? An 80mm ED model. The “ED” business means the false color, the purple fringing around bright objects, that is a characteristic of non-ED (achromatic) refracting telescopes will be low.

An 80 ED can be an incredibly powerful tool for astrophotography, allowing you to take wide-field shots of even very dim objects. What matters for extended objects like nebulae and galaxies when imaging is not aperture, but f-ratio. The lower it is, the less exposure time you will need, the deeper you can go, and the wider your field of view will be. How much money are we talking? Explore Scientific will sell you a nice 80mm triplet ED/APO telescope for just a little over 500 dollars.

You’ve just bought a mount, though, and 500 new or used sounds like a lot. Can you go cheaper? You can:  with an achromat. Yeah, I hear the veteran astrophotographers howling: “Rod, how can you recommend an achro? Especially a medium-fast achromat? You can’t take pictures with one. There’ll be horrible purple halos around even dimmer stars.”

Yes, I know there will be the dread color purple. But I also know 100mm achros are dirt cheap right now. The above mentioned Explore Scientific offers the very fine 4-inch f/6.5 AR102 for as little as 300 dollars on sale. Almost everything you need is in the box, including a decent finder and an excellent star diagonal. Despite the conventional wisdom, I decided to see whether one of these scopes—which is superior to an 80mm ED for visual use—could deliver pictures that would please a newbie, at least.

Of course, you’ll need a camera. If you’ve got a DSLR of any brand, use that. If you don’t, there is but one choice for the dollar-conscious newbie:  a Canon Digital Rebel. They aren’t expensive new (see the website of my fave dealer, B&H), and are dirt cheap used. Only caveat? Don’t go too old. Try to at least get the Rebel Xti. One of these classic Rebels still has more than enough features and capabilities for any beginner. My Xti is nearly a decade old, and I still use it for astro-imaging—frequently. While its top ISO (sensitivity) is 1600, its relatively large pixels mean it is quite sensitive.

To mount the camera in the scope’s focuser you’ll need a (2-inch if possible) prime focus adapter, available for a few bucks from most astro-dealers or from B&H. The DSLR is attached to that prime focus adapter using a T-ring, available for your camera brand from the same sources.

Do you need a computer? You will for image processing, and one can make focusing and image acquisition easier in the field (I use the wonderful program Nebulosity to control my DSLRs during picture taking), but you don’t need one. A simple and inexpensive remote shutter release for your camera, an “intervalometer” will do.

So, into the backyard. While the Atlas’ GEM head is heavy, it’s actually somewhat less awkward for me to lift onto the tripod than my CGEM for some reason. Once I had it on the tripod with the counterweight on the counterweight shaft, it was pretty simple to finish the setup:  mount the scope, in this case the AR102, and balance it so it was slightly east-heavy (to keep the RA gears meshed). That only required one 11-pound Synta pancake weight halfway up the declination shaft. Plug in power (an AC adapter I got from Orion) and the hand control and I was done with the preliminaries. And, naturally, right after that, the clouds came.

Before the evening was over, I was able to get a few cloud free minutes, however. Enough to allow me to polar align the mount and check it out (I hadn’t used the Atlas since the 2015 Peach State Star Gaze).  To polar align, I follow a two-part procedure. The first part uses the mount’s built in polar alignment borescope.

M15 before processing for chromatic aberration...
First, I rotate the mount in RA until the little circle on the polar borescope reticle where Polaris goes is on the bottom, and set the RA setting circle to “0”. I then turn on the mount and after I enter time/date/location it gives me Polaris’ current hour angle. I rotate the mount in RA until that “time” is under the RA circle’s pointer. With the little circle where it should be, I move Polaris into it using the mount’s altitude and azimuth adjusters (only).

The above will generally give a good enough polar alignment to allow reasonable length—two or three minute—sub exposures on the camera. It’s easy enough to tighten the alignment up a bit if desired, though, with part two of the process, using the built in polar alignment in the hand control. To do that, I complete a three-star goto alignment with the mount and then select Polar Alignment from the setup menu. From there, the process is nearly the same as the AllStar polar alignment used in Synta’s Celestron branded mounts.

To do a polar alignment with the hand control, I choose a bright star (one due south is best), slew to it, and begin the polar alignment routine. The hand control instructs me to center the star in the eyepiece, and then slews away from it. I use the altitude adjuster on the mount to get the star as close to the center of the field as I can get it. After I press Enter, the mount slews again, and I re-center the star using the azimuth adjusters on the mount. When that’s done the process is complete. The manual warns you may want to redo the goto alignment after a polar alignment, but I usually find that unnecessary.

All done, I did a few gotos to see how the mount was performing. It’s no secret the pointing accuracy of the Atlas is not nearly as good as that of the CGEM, with its famous 2 + 4 star alignment, but the Atlas’ three-star alignment is usually quite good enough with a widefield refractor onboard.

Anyhow, anything I requested from one side of the sky to the other was always somewhere in the field of my 8mm Ethos ocular (83x). The Atlas would not be my choice for video astronomy, where I might want to go to 20 or 30 targets over the course of an evening, and where I’d need the mount to put those targets on the small chip of a video camera, but the Atlas with its SynScan goto system is more than sufficient for visual use or for going to a couple of astrophoto targets a night.

Just after the mount centered the Dumbbell Nebula dead center in the field of my 25mm Bresser eyepiece (we’ll address the current crop of wide field bargain basement eyepieces like the Bresser some Sunday soon), the clouds poured in again and M27 faded out. I threw the big switch, covered the scope, and repaired to the den for some Agents of Shield action.

After...
While we had plenty of clouds for several days, we didn’t have a drop of rain—this has been one of the driest falls I can remember—so I was able to leave the Atlas and the AR102 set up in our secure backyard covered by one of the excellent Telegizmos scope covers. Finally, last Friday evening, the clouds departed and I was able to get started.

While I purposefully kept things as simple as possible, not even controlling the mount with the laptop, I did use Nebulosity for image acquisition. With the way my eyes are in these latter days, I simply find it too difficult to focus on a DSLR’s small display, even with zoom enabled.

Using Nebulosity, I can focus with the 17.3-inch screen of my Toshiba, and, using the program’s fine-focus mode, get images as sharp as possible. I thought that would be critical when using the AR102, as any misfocus would make chromatic aberration all the worse. I focused on Vega and the dimmer stars in its field, and when done sent the scope to my first target, M27, using the SynScan HC, which put the nebula almost in the center of the frame.

Let me pay Explore Scientific a big complement right here. The Crayford style focuser on the AR102 proved to be just about perfect. Not only did it have plenty of range, more than enough to focus the the Canon and the (excellent) Hotech field-flattener I used in lieu of a prime focus adapter (couldn’t find my plain prime focus adapter anywhere), its fine focus control made dialing in exact focus a joy. The draw-tube never slipped or threatened to with the Xti onboard, even when I pointed at M15, which was riding high.

In order to eliminate the necessity of guiding, I set the camera’s sensitivity to the maximum, ASA 1600, and limited my exposures to 30-seconds. That resulted in perfectly round stars in almost all my frames and had the benefit of keeping the background reasonably dark given my somewhat bright skies. Despite the typically bright suburban skies, it was apparent sky darkness was good enough to allow even a novice without a lot of image processing experience to get plenty of good stuff.

Alrighty, then. I told Nebulosity to give me 30 30-second sub-frames, and it began clicking them off. How was the chromatic aberration? Oh, the brighter stars definitely had purple haloes. I didn’t worry about that, and didn’t add any kind of filter to the imaging train. I’d decided that in the interests of simplicity I’d do any "filtering" after the fact, during post processing. I am also of the opinion that deep sky results are usually better if you don’t use filters of any kind during exposures. I wandered back inside to watch TV. The mount was tracking well, and Nebulosity was doing its thing without a hitch, so there was no need for me to stay outside kibitzing.

When the M27 sequence was done, I used the HC to go to M15, the great globular cluster in Pegasus. There is a magnitude 6 star in the field with M15, and I figured that would provide a good test of my ability to suppress chromatic aberration during image processing. Indeed, I could see the star had a pretty extensive bright purple halo even in the short subs. Again, I didn’t worry, just let the mount, scope, and camera do their thing.

M27
I was smart enough not to examine the M27 and M15 sub-frames after the last target, M15, was done. Pictures always look much better in the morning. I just shut down, covered the scope, and hauled the laptop inside. Despite not examining the subs, I was pretty sure  what I had gotten, and gotten so easily and simply, would have more than thrilled me when I was a novice.

Next morning, I set about to process my pictures, beginning by stacking the sub-frames into single images of M15 and M27 using Nebulosity’s built in image stacking routine (best in the business in my opinion). When I was done, I was not surprised to see that the brighter stars were really purple, but, again, I did not panic.

There are various ways to remove the purple halos of chromatic aberration in post processing. In the interests of simplicity, I decided to do as little as possible. There are ways to reduce not only the color purple, but the sizes of the haloes around the stars using Photoshop. I’ve experimented with that in the past with a friend’s achromatic images. Photoshop is expensive, however, and the procedure not overly simple for a novice. Instead, I used the built-in routine in another Adobe program, Lightroom.

The advantages of using Lightroom is that it is relatively inexpensive and does a lot, even including a built-in routine to remove that nasty purple. All that is required is to move a couple of sliders and you are done. True, the haloes remain, but they are no longer purple and are much less intrusive. Again, there are ways to reduce the size of the halos and the star disks themselves, and if you out there in blog-land have a good (and simple) method of doing that, I’d love to hear about it.

And that was that. Well, except for a little level-adjusting and some minor sharpening on M15. My resulting images are not masterpieces, but they certainly blow away many of the astrophotos I took in the film era. As above, I know, know, I’d have been thrilled to get these results when I was wet-behind-the-ears. I’d have been thrilled to get deep sky pictures so easily.

What’s next? While these pictures look pretty good, they could have used a little more exposure, so why don’t we talk about the art of autoguiding, autoguiding simply some Sunday soon?  For now? Why don’t y’all get outside and see what you can get of the deep sky without a lot of effort?

Sunday, November 13, 2016

 

Issue #517: Beginning the Messier Homestretch


M92
The 2016 Deep South Star Gaze is now done, and with it my star partying for the year. And after weeks of unbelievably dry conditions and mostly clear skies, the clouds and rain are back. That means it’s time to continue my detailed observing guide to the Messier objects, starting with a good one.

M92

We begin with Hercules’ other globular cluster, M92. I didn’t spend much time with this star cluster as a youth, not because it wasn’t good, but because, as everybody points out, it is much overshadowed by nearby M13, which I tended to obsess over. I spent my summer evenings in Hercules trying to somehow, some way coax a little resolution out of the Great Globular with my puny Palomar Junior Newtonian.

While Messier 92 is a nice object, it is in no way a first rank globular as some pundits claim. Even if M13 were not in the same constellation stealing its thunder, it still would still be considered an also ran. It is not an M13, but it is also not an M5, an M3 an M2 an M15 or an M22. It’s better than M30 and M53, but is definitely a second-string Messier glob.

Which doesn’t mean M92 doesn’t look stupendous under the proper conditions. At a dark site, this Shapley-Sawyer Class IV globular is busted into hordes of pinpoints by a 6 or 8-inch telescope, and in a 10-inch it begins to make you think it really is competition for the top globs—well until you slew over to M22, that is. Still, at magnitude 6.4 and 14.0’ across M92 is, yes, a showpiece.

Alrighty, then, let’s have a look. If you, like me, use non-goto, non-DSC equipped telescopes at least some of the time, rest assured this one will not cause any object-locating heartburn. To find it with my Rigel Quick Finder equipped 10-inch dobbie, Zelda, I insert a medium-low power eyepiece and position the bullseye on a spot in space that forms a near 90-degree triangle with Eta and Pi Hercules. Our target lies 6-degrees north of Pi and is bright enough that just a little slewing around always turns it up after I position the telescope in its approximate location.

What’s it like in the eyepiece? In my backyard, my 3 – 4-inch refractors can make it look grainy, even on somewhat poor evenings. I was out just the other night with my 3-inch f/11 SkyWatcher refractor, and marveled that not only was M92 easy to find on a hazy evening, but that it looked like a globular. While not resolved, it wasn’t just a smudge, either.

As with most globs, every increase in aperture makes the cluster better, but this one, second-string though it may be, doesn’t require a large scope to look terrific, as I found out one night at the club dark site with my ETX125, a 5-inch MCT: “The core looks almost square at 170x. The outer region is round and populated by many, many stars, some of which hold steady with direct vision, and some of which tend to wink in and out.”

M93

M93 sketched with my Pal Jr...
Winter is open cluster time, and one of the better winter galactics is magnificent M93 lurking in oft-ignored constellation, Puppis. What we have here is a group of about 15 – 20 bright stars and maybe 50 dimmer ones spread over an area of about 20-minutes of arc, In other words:  perfect for small scopes. Well, depending on your site, anyway. M93 has a rather southerly declination, -23-degrees 51’, and for many observers that puts it a little close to the horizon some of the time, especially considering its somewhat subdued magnitude, 10.93. It is still worth plenty of eyepiece time, though.

Finding M93 manually is not difficult if you can see the magnitude 3.3 star Xi Puppis. The problem for most of you will be that while you can see this star, “Asmidiske,” which lies some 16-degrees southeast of Sirius, you may not be familiar enough with the stars of Puppis to know which one of the constellation’s scattered suns it is. As I’ve often said, if you want to star-hop efficiently, you have got to familiarize yourself with the less well-known and visited constellations. Once you’ve got Xi in the finder, the cluster can be easily swept up a degree-and-a-half to the west-southwest. Despite its somewhat dim nature, M93 should be visible in a low power eyepiece in the backyard.

I often looked at M93 when I lived in my pre-Chaos Manor South downtown home in the 1980s. For a (short) while, the largest telescopes I owned were 4.25-inch and 6-inch reflectors, and given the rather severe light pollution, open clusters were often about all I could see well. While M93 was sometimes in the trees, it never failed to thrill me. Occasionally, as in the accompanying sketch from those days, all I could see with my 4-inch was the central group of brighter stars, but it still looked great. From a dark site in my modern 4 and 5-inch refractors, this field just comes alive with hordes of small stars.

M94, the Croc’s Eye Galaxy

What’s troubling you, bunky? Your spring backyard sky is hazy and the light pollution is heavy, but you still long to see a galaxy? I’ve got one your small scope can pull out every single time, M94 in Canes Venatici. It’s an Sb spiral with a preternaturally bright center as befits its status as a Seyfert galaxy and which allows it to be visible in 3 – 4-inch telescopes with ease in nasty skies.

M94 imaged with the old DSI...
There is absolutely no difficulty involved in finding M94. It is a degree-and-a-half northeast of a line drawn between Canes’ two prominent stars, Cor Caroli (Alpha), and Chara (Beta). Position your scope almost midway between the two hunting dogs—maybe a smidge closer to the Alpha dog—and then slew that 1.5-degrees northeast. The only possible diff is that at low power M94 can resemble a slightly bloated star.

And a slightly bloated star surrounded by some thin haze is all you will see in a small scope from the backyard. Without larger aperture (or a camera) and a dark site, you’ll fail to understand why this object is “the Croc’s Eye.” The reason for that moniker is that in large aperture scopes at high power (or in my in my C8 equipped with Meade’s old DSI camera as here) you begin to see spiral structure surrounding the bright core, which is in turn surrounded by a faint ring (a starburst region). The combination of these things does make this object somewhat resemble a reptile’s eye.

M95

When it comes to spring galaxies from the backyard, we go from the trivially easy to the considerably harder. M95, a magnitude 10.6, 7.1’ x 4.3’ Sb spiral is not impossible, but at times it is unavailable to a 4-inch or even a 6-inch under compromised skies. It’s still a nice catch, however, and if you’ve got a 10-inch available you’ll like the field, which includes its sister galaxy, M96, just 42’ to the east.

Finding M95 without electronic assistance is not always easy. The only ready signpost is magnitude 5.45 Kappa Leonis in Leo the Lion’s “belly” area. The galaxy lies 2-degrees 33’ to the south. A better way to go might be to find the much more prominent galaxy M105 first. From there it’s a trip of only 1-degree 17’ to the southwest to get on the M95 field.

Once there, don’t expect too much if you don’t have dark skies. Even in my 11-inch SCT, M95 was subdued in suburbia: “Like M96, M95 is basically a round fuzzball in light pollution. Stellar core. It is slightly easier than M96.TeleVue Panoptic 22mm, 127x.” Frankly, even under dark skies with larger scopes, don’t expect much else.

M96

M96 is M95’s companion galaxy, and is similar visually to M95. While it’s somewhat brighter at magnitude 10.1, it is also a little larger 7.6’ x 5.0’, and actually slightly less prominent to my eye. Like M95, it cries out for 10-inches of aperture in the average backyard if you want to make things easy. Which doesn’t mean you can’t spot it with a smaller instrument on a good evening. I’ve seen both it and its neighbor with my C102 refractor on haze-free spring nights.

If you’ve found M95, you’ve found M96. Just remember:  M96 is on the east, and M95 is on the west.

ATIK Infinity M97...
What can you see once you are there? In 8-inch – 10-inch instruments, you’ll see a somewhat elongated fuzzy, maybe 2’ worth, with a brighter center. In larger scopes at better sites, the galaxy increases in size but still doesn’t give up much more in the way of detail.

M97

M97, the famous Owl (planetary) Nebula in Ursa Major has, as I’ve said before, a reputation for toughness. That’s an undeserved reputation in this day of OIII filters, which can make old Owley pop out of some pretty bright skies. But you know what? I’ve spotted it with a suburban 3-inch without a filter. Oh, it was much better with the filter than without it, but it was nevertheless detectible sans LPR filter. With an OIII? My 60mm ETX has pulled it out of remarkably putrid skies.

It’s no hassle to find the Owl the old-fashioned way, as it lies only 2-degrees 20’ east-southeast of a prominent star, magnitude 2.3 Merak in the bowl of the dipper. Put a filter on a 25mm eyepiece, scan in that direction, and the large (3’24” x 3’18”) round glow (magnitude 9.9) of the Owl will enter your eyepiece.

There, in a small scope, that’s about it: a round smudge. A larger telescope, a 10 - 12-inch may, may reveal the holy grail of owl-watcher,  the two dark spots that are its eyes and which are the reason this nebula is the “Owl.” In suburban skies, they are most often only suspected in these medium-sized scopes. At a dark site, they are considerably easier, if not always easy. Large aperture telescopes under excellent conditions may also reveal the several 16th magnitude range stars involved in the nebula.

M98

We end on another spring object, a galaxy, M98 in Coma Berenices, which lies on the edge of the great mass Virgo of galaxies. How much you will like this magnitude 10.14, 9’48” x 2’48” edge-on Sab island universe depends, as it usually does with galaxies, upon your aperture and your skies. 
From the suburbs, it can be visible as an elongated something in an 8-inch. A 10-inch begins to bring out its edge-on galaxy nature, but you need to get out where it is dark to really appreciate this one.

M98
The main problem here is not the seeing but the finding. Take it from me:  use goto or DSCs on this critter. The galaxy lies in the fairly star poor area east of Denebola, about 6.0’ from that bright star. If you don’t have access to an electronically enabled scope, detailed computer finder charts can get you there, but it will probably not be fun.

When you are on the galaxy, I hope you are on it at your club dark site. There, in a 10 – 12-inch, or, better, a 16-inch, M98 can be spectacular, a long, luminous spindle with a bright and tiny nucleus floating in the black void.

And so, we end it for this time with only two more installments to go. Given the way the skies look at the moment—the November storms are on their way—it appears you may actually get one of those installments next week. I have the EQ-6 mount and a refractor set up in the backyard right now in hopes of bringing you something different, but the weather gods clearly say “no.”

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