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Old 37 Under the Stars with a DSLR
Astrograph, eh? Why would I want to use something other than one o’ my beloved SCTs, anyhow? I’ve been imaging with my friendly CATs for years, but that doesn’t mean I use ‘em for everything or think they are perfect for everything. Let’s face it, 2000mm is a lot of focal length to deal with, and if, like me, you must use your scope in portable mode and are just naturally lazy about things like polar alignment (I sure am), cuttin’ down them mms helps. A lot. Get down to about 800 – 900mm of focal length and deep sky snapshooting becomes much easier. It’s finally possible to get nice, round stars without winding up needing a hair transplant.
The most aggravating thing about focal reducers and reducer/correctors is that they cause a vignetting-type gradient in images with all but the smallest of small-chip CCD cameras; especially if you are shooting from skies that ain’t perfect. This “porthole effect” can be removed with a good flat-field frame, but since I work with a portable scope, it’s not very convenient for me to do flat fields. To do ‘em, your scope must be perfectly focused, and the camera can’t be removed/moved from the time you do the flats until you are finished imagin’. For me, that means leaving the focuser untouched run to run and arriving at the site well before sundown to do my T-shirt flats (shoot the sky at sundown with a “filter”made of T-shirt material over the scope’s end). Yeah, it’s possible to use light-boxes and other contraptions to do flats after dark when you can focus the scope on a convenient star, but that’s one more piece o’ gear to worry about and I am nearly overwhelmed in that regard already. That ain’t the only fly wigglin’ in the reducer ointment, neither. If there is an overly bright star in the field, the f/6.3 reducer/corrector, especially, tends to generate WEIRD-lookin’ reflections. In fact, Bubba down the street got all het-up when he mistook one of these odd blobs for a saucerful of Little Gray Dudes from Zeta Reticuli II.
Sure I’ve got my small-aperture APOs for those times when, for one reason or anudder, I don’t want to use my SCTs (having to track across the Local Meridian to get a shot and chancing mirror flop bein’ one). But it would on occasion be nice to have a little more aperture and image scale than these refractors provide. What to do? First thing I thought about was the 6-inch f/9 Richey-Chrétien the boys n’ gals at Astronomics are preparing to sell. I also considered the aforementioned new Maksutov Newtonian from Orion, a 7-inch f/5.3. I like new gear, sure, but I’m awful cheap as well, and I wasn’t overly happy at the prospect of shellin’ out 1300 bucks for either scope. Also, in the case of the R/C, I’d be right back in reducer-town in order to make its f/9 optical train suitably fast (a dedicated reducer is also not yet available). At the time I was pondering these weighty issues, the 37-year-old scope was comin’ together, and I began to wonder whether it might serve as an alternative astrograph and save Unk a grand or more. This hope was one of the reasons I opted for a diffraction spike eliminatin’ curved spider to hold up Ol’ 37’s secondary: If I want star spikes in an image I will put them there with Photoshop.
How did it work out? How did Ol’ 37 do as a picture taker? It wasn’t till last night that I was able to find out--sorta. Oh, I’d had a brief look at the Moon, Jupiter, and a few bright DSOs the evenin’ after my good buddy Pat finished work on her, but cloudy nights and sea-trials onboard the U.S. Navy’s latest AEGIS destroyer, TRUXTON (a grand lady) meant I hadn’t touched the scope over the following month. The prospect of clear skies for this Saturday night induced me to enlist daughter Lizbeth’s help and start loadin’ up the ton of gear required for an imagin’ run at the PSAS darksite. What did we cram into the Toyota? Here’s what we took, which will give some insight into Unk’s minimalist approach to astro-imaging.
Mount: As many of y’all know—from hearin’ me go on and on about it over the last couple of years—my long runnin’ love affair with fork mounts is over—for imaging, anyway. I find a German equatorial mount, a GEM, easier to manage for astrophotography: easier to balance, easier to align. It’s also more versatile, since I can slap on whichever OTA is called for on any given evenin’. Yeah, I looked longingly at the AP900 and Mach1, the Losmandy Titan, and the CGE in descending order of painful expensiveness. At the low end, the CGE at 3000 dollars (or the very similar Losmandy G11) was still more than I could stomach, given that I might get out to do serious imaging three or four times a year on average at the moment. Long story short? I settled on the Orion (Synta) Atlas (EQ6). Certainly it is not an AP or even a Losmandy, but given the few times I’ve been able to use it over the last year, the Atlas has proven itself to be a capable imager, and it will be a long time before I outgrow it.
Camera: While I often use a wonderful SBIG ST2000, I’ve got hooked on the DSLR thing of late. I mean, what’s not to like? With a chip larger than all but the most expensive “real” CCD cameras, and very good lookin’ one-shot color, my Canon Rebel Xti (aka 400d) suits me to a tee. If nothin’ else, it is so film-SLR-like that, given my three decades of shooting with old-fashion SLRs, using it for astrophotography has been as easy as fallin’ off the proverbial log. Only “problem”? These cameras’ APS size chips are covered by an IR block filter. That makes snaps o’ Miss Dorothy look good, but blocks the red light of nebulae. It is possible to have this filter removed, but I have not been moved to do so thus far. The bright nebulae I usually go after look right good in the Canon, IR block or no.
Guidescope: In these days of CCD guidecams, you really don’t need much of a guidescope. For starters, forget about needin’ one with a focal length close to that of the imaging scope. Silicon don’t care. I’ve used both a William Optics 66mm “SD” and a good, ol’ Short Tube 80 successfully. I’ve been using the 80 a bit more recently, since it seems to (maybe) show a few more guidestars in any given field than the 66, but the difference is minor.
Laptop: My laptop PC is several years old, but thanks to Miss Dorothy, who encouraged me to buy the fastest one I could find, this Toshiba 3.2 gig machine is still an outstanding performer. It is quite power hungry, but I have learned to deal with that. It is also as heavy as a ton of bricks, but that’s only a consideration when totin’ it through an airport.
Software: What do I need a consarned laptop for anyways? The beauty of DSLRs is that they can be used just like 35mm SLRs, right? No stinkin’ computer needed. Yes and no. As I pointed out in a recent edition of this very blog, a laptop just makes DSLRing easier, ‘specially when it comes to focusin’. I don’t know about you, but I find it easier to focus a star on a bright laptop screen than in a dim and tiny DSLR viewfinder--or even with one of the “live” display screens more and more cameras are featuring. Which program do I use? Nebulosity. This was the first DSLR-centric one I tried when I got my Canon, and I have not felt the need to upgrade. It (now in Version 2) is inexpensive at 60 bucks, and will do ever’thing I—and even many advanced imagers--want done. Wut else? Naturally, if you’re gonna lowball it on the mount like I did, you are not gonna be makin’ very long unguided exposures. I like to do 2 – 3 minute integrations, and so, need an autoguiding program. I have yet to find anything better than PHD Guiding. It is free, a big recommendation in my book, but, best of all, it really is “push here dummy.” Most of the time, I just hit the “go” button and it works.
Guide Camera: I hear good things about Orion’s inexpensive StarShoot autoguider, but I gotta say my Meade DSI (the original color version) still works fine after several years of use. No, it’s probably not the most sensitive guidecam out there, but, nevertheless, I have never found a field where it wouldn’t show at least one or two guide-worthy sparklers.
Battery: Combine a honkin’ big laptop with Meade’s surprisingly power hungry little DSI camera (it draws its current from the USB bus), and you can bet a laptop battery ain’t gonna keep things rollin’ for long. Even a jumpstart battery pack ain’t enough for me. What I use is a 75 amp hour trolling motor battery (maybe called a “deep cycle marine battery” in your neck of the woods). In the interest of preservin’ even this big battery, I run the computer off one of them little 12vdc laptop adapters. These DC – DC supplies are much easier on the battery than what I used to use to power the computer: the laptop's normal power supply plugged into a DC to AC “inverter.” I still use the inverter, however. Turned out the DSI draws enough current to make the laptop’s DC to DC supply trip offline. My solution at this time is to use an AC powered USB hub plugged into the inverter, which is, of course, connected to my battery. I know there are DC powered USB hubs out there, and I’ll run one of ‘em down one day, but this setup will go all night with the DSLR—and even the SBIG despite its electron-gobblin’ Peltier cooler.
Hookin’ it all together: Lizbeth and I packed this ton o’ astrojunk in the car and headed out to our Tanner-Williams, Alabama darksite. When unpacked, we had enough stuff on the field to make our end of it look like the headquarters of a South Seas cargo cult, and I admit I began feelin’ a bit overwhelmed. The last shot I took before this night was of M42 when it was on the Meridian, and I was havin’ a hard time remembering what went where and where to start. Starting with the relatively friendly scope and mount allowed me to dispel the deer-in-the-headlights blues. By the way, as you can see in the image, the guidescope and the imagin’ scope are on a side by side mount (from ADM). Do I think this is better than piggybacking the guidescope on the mainscope? Not necessarily. A piggyback combo is maybe a little easier to balance. The side-by-side has the advantage, however of allowing me to swap scopes and guidescopes freely without having to acquire and keep up with multiple piggyback brackets and guidescope rings.
Hookup of all them computer widgets? I took the bit in my teeth and got to work. The guide camera goes in the guidescope via a prime focus adapter (you can’t reach focus if you just insert a guide camera into a refractor’s drawtube; they are designed to be used with diagonals and won’t provide a camera enough backfocus without a diagonal). The guidecam’s USB cable goes to the USB hub. Next up was the Canon DSLR. It requires two connections; one from its “remote” jack to Shoestring Astronomy’s DSUSB DSLR shutter-interface box. The Rebel also requires a connection from the USB port on the camera to the USB hub. This USB connection is for image download, while the shutter connection is for, yep, shutter control--and also enables things like ISO and exposure duration to be set from the PC. I understand the most recent Canon DSLRs don’t need this remote connection, with everything able to be done via the USB line. One final cable is required, an ST4-style one for autoguiding. That goes between a Shoestring guide adapter on the laptop (I have the parallel port version, but a USB model is available) and the autoguider port on the Atlas. With all these cables runnin’ ever' which-way, take care to dress ‘em so they don’t get tangled on the tripod and won’t get tripped over (I’m notorious for that). USB “extension cords” are a lifesaver here and can be obtained in Wally World or your computer-junk retailer of choice.
As you might expect, by the time I finished with all this stuff it was getting dark enough to get polar aligned. What do I do in that regard? Y’all know I hate drift aligning. To avoid that mess, I rely on the Atlas’ polar alignment scope, which is generally more than good enough if I am careful. In my opinion, if you are autoguiding you really don’t need to drift no more. Yeah, I know the high resolution imagers will tell you that is no way to get the very smallest, tightest stars. Me? I am just happy if my stars are round, and and I haven’t had much trouble with that despite my aversion to watching a star drift in the crosshairs. Like I said, I try to do a good job with the polar scope.
I do that by first turning the RA axis until that little circle on the reticle where you put Polaris is straight down in the field of the polar scope. I adjust the mount in RA until Polaris moves straight up and down from reticle to the circle. That defines the “0 hour” position for the polar scope, and I then move the RA setting circle until it indicates 0h and lock it down. Next step is to figger out the current Polaris Hour Angle. You can do that with a PC program, or, if you have the Atlas, the SynScan HC will tell you the Hour Angle once you’ve inputted date, time, and position. I like to use a cool (and free) little program called Polarisfinder. Not only does it give the current Hour Angle, it displays a graphic of where the little circle should go in the field of the polar scope. On this evening, I, as usual, loosened up the RA and moved the scope until the RA circle indicated the correct hour angle as indicated in Polarisfinder. I then twiddled the mount’s altitude and azimuth adjusters to put Polaris smack in that circle. But something didn’t seem quite right.
I went ahead and fired up the Atlas HC, even though it was not quite dark enough to do the go-to alignment yet. The hour angle the program had given me kinda-sorta sounded “funny.” Indeed, what the HC said was entirely different and more reasonable. What the? I checked Polarisfinder again, and it hit me: the program is of European origin and uses the European date format, dd/mm/yy instead of us Yankees’ (ulp) mm/dd/yy. That corrected, I readjusted the polar alignment. Lesson learned? If you are not completely familiar with a program, leave it at home.
If you’re using a Newtonian, it’s always wise to check the collimation of the scope prior to beginning an imaging run. Even if you use a mirror cell that locks down purty tight, check it. Be obsessive. Small collimation errors that aren’t apparent to the eye, even at higher magnifications, will be all too obvious in pictures.
I pulled out my combo Cheshire/crosshair sight tube (from Celestron) and prepared to give Ol’ 37 a final tweak or three. Alas. I’d fooled around with polar alignment long enough that it was now dark and the Cheshire had become near about useless. Oh, I was able to get close by using a flashlight pointed down the tube, but it wasn’t easy, and my collimation is obviously off when you blow up last night’s pix. Moral of the story: collimate as soon as you hit the field. If you don’t want to do that, or tend to arrive onsite as dusk comes, buy and use a good laser collimator.
Next up was go-to alignment. I normally use the EQMOD ASCOM scope driver program instead of the hand control, which makes for easy and accurate go-to alignments. You simply click on three--or six, or however many you want--stars on the display of the planetarium (any ASCOM compliant planetarium) you use in conjunction with EQMOD, send the scope on go-tos to these stars, center ‘em, and tell EQMOD to use ‘em as the alignment stars. Looking at Cartes du Ciel’s screen makes it easy to figure out which stars are good picks. Just choose three that form a nice, big, triangle. The SynScan HC? You are presented with a seemingly patternless list of alignment star choices, and it’s difficult for me to decide which ones are best to use from this list of proper names (why in the hell can’t go-to scope makers identify alignment stars as, for example, “Beta Herculis” instead of “Kornephoros”?).
Yeah, I thought runnin’ the mount with a hand control I’d used once previously, nearly a year ago, would be “simpler” than usin’ EQMOD. Not! Yes, the SynScan HC looks a lot like my NexStar HC, but it is a totally different beast. Trying to use the same button pushes as on the NS controller resulted in me locking the puppy up and shuttin’ off tracking. I had to start the go-to align over, wasting more fleeting minutes. If you are not thoroughly versed in the use of a piece of equipment, save learning it for the backyard, not for a dark site during an imaging run.
With the mount more-or-less aligned, I was able to proceed to focusing the guide camera and the imaging camera. My usual procedure is to focus up on the final go-to alignment star, increasing exposure when that bright one is as small as I can get it so as to show up dim field stars. Nebulosity has an excellent fine focus tool that can be used on these dimmer (non-saturated) stars to obtain precise focus easily. If you are careful, anyhow.
After wastin’ time redoing the polar alignment and the go-to alignment, I made a critical error: I got in a hurry. What I should have done was recheck focus once the scope landed on M13, my first target. A globular cluster is incredibly unforgiving of mis-focus, and it’s obvious in my images that the tiny stars that form this cluster could have been tighter. Be unrelenting about focus and never, ever, hurry. That’s a sure way to make the entire evening a waste of time. Luckily I was close enough to focus to make my final images acceptable--barely.
Alright, it was finally time for the pay-off. I centered M13 in the frame using Nebulosity’s “frame and focus mode” (it fires your DSLR’s shutter continuously until you tell it to stop). I then let her go: “Gimmee 20 three-minute frames.” The first one to pop onto the display looked good. Guiding was right on—always my chief concern. As a matter of fact, guiding was the only thing that really went well last night. PHD is just flat out amazing. When I arrived at M13, I clicked on a star on PHD’s display, one suitably near the glob, hit the “guide” button, and PHD calibrated and started guiding without complaint, keeping the little star dead-nuts-on for as long as I desired.
OK…first exposure was done. On to the next frame. When it appeared, frame 2 seemed a little odd. Consecutive “subs” of the same target always look a little different—seeing changes a bit and the stars sharpen or unsharpen; the field background density changes a little; etc. Strangely, though, the second frame looked flat-out identical to the first one. As did the third-un. It was not until the 15th frame, about an hour later, that one of my few remaining neuron’s fired: “Rod, you are not hearing the shutter fire.” The Rebel makes an easily audible “motor drive” sound when it exposes. I was not hearing that. A little experimentation revealed that sometimes the shutter would fire, sometimes—most times--it would not.
Lizbeth and I spent at least a half hour diagnosing the problem. Turning the camera off and on. Rebooting the PC. Unplugging the camera’s USB cable and plugging it back in. Finally, I spied the little DSUSB shutter interface box. “Hmmm…the cord that goes to the remote plugs into a mini-jack on this box. I wonder if it’s
All over but the cryin’? Well, by 11:00 pm conditions had degraded to the point where it was obvious that Lizbeth and I might as well start packing up (our fellow club members had departed an hour previously to the tune of plenty of—OOOPS!—accidentally illuminated headlights and running lights). As we were proceeding to pack 10-pounds of stuff into the proverbial 5-pound bag, I felt a bit put out. 8-dadblasted hours in the damp cold and not a whole lot to show for it, prob’ly.
As always, though, things looked better this morning over a cup of coffee. One smart thing I’ve learned is NEVER EVER LOOK AT YOUR EVENIN’S IMAGES AS SOON YOU GET HOME. It’s late, you’re tired, and have spent the better part of an hour, usually, unloading a ton of gear. Even if your name is “Jack Newton” your pix are gonna look just like hell. In the morning light, a waltz through the hard drive revealed that Lizbeth and I had brought home a few OK frames. Certainly nothing I would enter in a contest or even want to show my friends—you all, that is—but good enough to tell the tale on the 37-Year-Old Telescope. Verdict?
Brothers and sisters, you know I am not really a Newtonian kind of a dude, but I must admit the stars look very good out to nearly the field edge in the Rebel (love that name!) frames. With the simple addition of an inexpensive Baader coma corrector, I’m a-betting they would be darned near perfect. I don’t think I have to spend over a grand afterall (not to say I might not if the gear-fever strikes). There is something else goin’ on too. I can tell you right now that I ain’t gonna be giving up my CATs for lion’s share of the imaging duties ‘round here, but Ol’ 37 does deliver one thing they never will. The ineffable feeling that comes of looking at astrophotos--no matter how humble and screwed-up they might be--that are the product of a piece of glass you sweated and dreamed over.