Blue Collar Scientist

Last night was the first run of the new control system for the 0.8 meter telescope at Junk Bond (take a crappy video tour here), and everything worked great. That’s really no surprise, because this is probably the best-tested high level control system and observation scheduler that I’ve ever written. It incorporates a number of new features (most of which are strategic secrets), and also has a lot more error condition handling and correction in it. I’ve been putting it through its paces on the simulators for the last 12 weeks, and that work has definitely paid off in a flawless first-night deployment run with a very complicated schedule request from the astronomer.

Another thing I did last night was take time-lapse photos of the night sky. I have a Canon 5D with a circular fisheye, so I get full-sky coverage with the horizon all around, and for quite a while now I’ve wanted to make a dusk-to-dawn animation of the night sky. I did my first experiments along these lines back in February of 2007, but on my trip then I didn’t have the best skies to play with - we had a lot of clouds. So I ended up getting only a single night, and that was interrupted by clouds that came in around 3:00 AM and started raining on the camera. These are obviously sub-optimal conditions for taking pictures of the stars. Still, it was enough to learn what I was doing wrong and figure out some solutions.

The first time out, I set up the camera on a tripod, pointing straight up, with an intervalometer controlling the exposures (an intervalometer is a doodad that takes a picture of a certain duration every so many seconds or mintues). I elected to use 30 second exposures at ISO 1600 with a two-second refractory period. Periodically throughout the night I would swap out CF cards and batteries, which really sucked.

This time, things are way better. First, I’m running the camera off AC power, using a Canon adapter. That means I don’t need to swap batteries all night, and I can get some sleep. Second, the camera is operating tethered, connected to my MacBook. This means that none of the images are stored on the CF card; they are downloaded directly to the MacBook hard drive. I bought Aperture solely for this purpose.

Now, I’ve tethered with my Windows PC’s before, and I’ve even tethered with Linux, and it can be a painful experience. Kinda like the Windows implementation TWAIN, but worse, you have to get a series of drivers and abstraction layers installed and working, creating the correct pipeline, before you start your tethering application. Typically one step of this process involves installing a camera driver from Canon, which you have to download from their disorganized and arcane website¹. If you don’t get it from their website you can install it from the CD that came with your camera - and hopefully you can avoid installing all the other crapware that comes on that disk. Besides this, Canon are not, in my opinion, the best at writing drivers (or supporting them), so the whole thing takes on the appearance of pig-herding exercise.

If you get all this driver software installed, you then need to tell the application you are using to open a tether with the camera. This usually works fine, once you get all the other stuff set up, but it is all just something of a pain in the neck.

But Aperture is a bit lot more elegant. I didn’t install any drivers at all; I just opened Aperture, selected “start tether,” and I was off to the races. Imagine that - two clicks and it works, no system configuration needed.

The upshot is that my camera took 1,400 exposures last night with essentially no intervention from me. Everything ran rock-steady the whole time and nothing blew up. That allowed me to concentrate on some other questions that I had about how to best take these images, namely, how to expose the fading twilight in the evening and brightening twilight in the morning so that the animation looked pretty much natural. It was non-obvious to me how to change the exposure to track the changing sky brightness to come up with a decent-looking movie.

It now appears that I have that figured out as well, so tonight, if it remains clear (and it sure looks like it will), I’ll be executing version 3.0 of my all-sky, all-night time lapse. I’m pretty excited about it, too!

1. One time I downloaded and installed a driver that only spoke Korean, to my dismay. [↩]