Ad Astra Observatory

Hi,

Although it was bitterly cold and windy out last night, and clouds kept threatening to roll in (which they never quite did), I was able to get some important proof-of-concept and maintenance work done last night.

I decided to check the polar alignment with 5-minute tests instead of the 2 minute tests I’d been previously running; a longer test gives a more accurate reading, but the test is, basically, hold down the “east” button for N seconds, then hold down the “west” button for N seconds, and see what the resulting photo looks like. In short, it’s all about beating the boredom, since you’re basically sitting around without being able to move your finger for 5 minutes at a time, followed by adjusting the mount by ever so little, lather, rinse, repeat. The 2 minute tests are bad enough, but the 5 minute tests are killers, and I had to run about 10 of them. ick. I started to think about how I could automate the process; seems like it would be dead simple to rig up a cable to make *this* electrical connection until it got a timer pulse from somewhere at which point it would switch to *that* electrical connection… hmm. An auto polar alignment doodad would rock.

I of course made a crucial error early in the evening that cost me a lot of time. I was running a polar alignment test and needed to put my head next to the drive to make sure it was silent, and bumped my head into the telescope. oops. But then I did 2 stupid things. 1) I didn’t immediately stop the test and restart it, and 2) I saw the screwy test results *and used them to make an adjustment to the mount*. stupid, stupid, stupid. I’ll never know if the mount was out of alignment in the first place, but I know that I had to mess with it for well over an hour before I got it back in alignment again. sigh.

OK. So then I knew that I was polar aligned (at least in RA; I didn’t have the energy to do Dec, too) for 5 minute stretches, which is what I was worried about when I got a bad 5-minute unguided image the other night. So I popped over to M13 again…

As an aside, a lot of people whine about (manual) setting circles; they get a bum rap in the amateur astronomy press. In contrast, manual setting circles are working pretty well for me. Maybe it’s just that the setting circles on this particular mount are large and easy to read and seem pretty accurate… but I really don’t see what people are whining about. You point at something whose position you know, you set the circles, then you’re good for the night. Pointing at M13 is all about looking it up in a table and then setting the mount to read those coordinates, and bang. There it is, in the eyepiece. I admit, you have to reset the RA axis every night (since the sky moves, if you don’t keep the drives running continuously, the RA circle will be off from night to night. The Dec axis will stay the same, however…), but to boot up the GOTO mount, I had to put in the (exact) time and date and then confirm about 5 screens worth of lat/lon/daylight savings info before it could recalibrate, so I don’t see how this is all that onerous of a task. shrug.

Anyway, I pointed over at M13, which is still a little on the low in the muck side of things near sundown, which is why I had to shoot over the top of the house (my wife was not happy about having to leave the lights off ): ). Anyway, hopping over with settings circles is crazy-easy (I may forgo digital setting circles as long as I can get my targets more or less on the CCD), and I decided to try out a 5 minute unguided exposure again. No joy. The 5 minute exposure was pretty bad. I mean, good enough that I could have guided out the error, no sweat. But definitely *not* “useable”. So rather than working out the kinks in the guiding system (that’s possibly a whole night’s worth of tinkering, or possibly it’ll all just happen like unto magic, but I wasn’t willing to risk it), I decided to set the mount up to fire off a sequence of 2 minute unguided exposures, just like I had on Tuesday night.

On Tuesday, I ran an hour’s worth of 30-sec images (that’s 120 images, if you’re keeping track), and then I set it up for another hour of 2-min images (30), but I got real tired around 20 images in, and let it run to 23 before I decided I really couldn’t do another 15 minutes to wait for the final 7 images to come in (I was still pretty jetlagged on Tuesday night), so I stopped at 23. I was too tired to transfer the images off of the
observatory laptop (one of these days, I *really* need to get it back on the internet…), but a random sampling of the 2-min images looked pretty good, and the 30sec ones were also looking good.

Last night, I set up for 90 minutes of 2-min images (45), and ran all the way through the sequence. A sampling showed a weird pattern of “every other” image being screwy, which is consistent with a worm gear cycle of 4.25 minutes; I must have gotten lucky on Tuesday. Again, it looked like all stuff that I could guide out.

While the 45 images were running, I decided to do some quickie processing on the 30-sec and 2-min images from Tuesday. Each of them definitely had more “data” than any of my previous attempts on M13 (these are 60 minutes and 46 minutes worth of data, compared to my 5 minute and 12 minute exposures that are on the webpage). Although the 30sec-produced photo is nice, I don’t think that it is quite a long enough exposure (at ISO 400) to really be compared “linearly” to the 2min-produced photo; that is, the 46 min-total 2 minute stack looks significantly smoother and brighter than the 60-min-total 30 second stack. I imagine that if I’d shot the 30sec images at ISO 1600, the results would have been more comparable (ISO 1600 = 4x faster than ISO 400; 2min = 4x more exposure than 30sec).

My plan, of course, is to combine the 45 2-min exposures from last night with the 23 from the previous night, and maybe add some more to the stack as well. If I could successfully get 3-4 hours of integration time on M13, I think that I could safely say that I’d gotten all the data out of it that I can.

Once I get the guidescope up and running, I should be able to easily tackle any length of exposure that is possible from the observatory with the current camera, scope, and filters.

But running unguided is so liberating, I may hold off for a little while. Maybe I’ll see how deep I can go with 2-min exposures (or maybe I’ll go nuts and decide to try out some 3-min ones, just for giggles.. (:

sic itur ad astra.