Here’s a picture I made for Astronaut Abby, who is the Earth liaison for current ISS astronaut Luca Parmitano (hence the #CatchLuca twitter hashtag). It may not be the best photo ever taken, but there are some interesting things to tell about it. First of all, I use Sputnik on my iPhone to know when the ISS passes over my location, at what angle, brightness, etc. It’s an awesome little app that you can use for free!
Now a typical pass of the ISS takes 2 or 3 minutes of visibility, so I had to take a long exposure. With my un-modded Canon PowerShot SX200 IS, the longest exposure is 15 seconds. You can take pretty nice pictures with a 15 second exposure as I did here, but what if you want to take longer exposures? Well, luckily there is an amazing free firmware patch for most Canon cameras available. It’s called CHDK. I’ve mentioned it in the past, but I got a few emails asking how to get it working, so let me explain.
The easiest way to get CHDK on an SD card is by using STICK, a free utility for OSX, Windows and Linux. Now on my Mac (currenty running OSX 10.8.4) I had to use the StickML.command. This launches you into super user mode in terminal, so it will ask you for your admin password.
If you use stick.command instead, it will fail later on, so be warned! Next an interface opens. You can simply drag an existing photo from your Canon camera on top if it to find the right firmware version for your specific camera. In Step 2, STICK will download the right firmware version of CHDK for you:
Of couse you need a dedicated SD card reader/writer to create a bootable image. STICK does not communicate directly with your camera. Insert a blank SD card into your card reader/writer and choose the appropriate device in STICK. Next click Continue to Install Step and the card will be formatted for CHDK. Because CHDK is a non permanent patch for your camera, you can easily have two distinct SD cards; one to take pictures or videos where everything is normal, and one with CHDK on it if you need the extra features.
When all is done, eject the card using STICK and the LOCK IT! This seems counter intuitive, but yes, you have to lock the card in order to use CHDK and take pictures with it. That’s right, click the little lock in the write disabled position:
This is just the way CHDK works. You can happily take photos with it in the locked position. Now go have fun with your camera with its extra menus. There are a lot of extra features, so try not to get overwhelmed. Basically find out how you can switch in and out of CHDK mode. In my case, that’s the Print button on the back of the camera. The usual Menu button will show an entirely different menu when you click it. If nothing else, you can use a setting such as this to make long exposures:
At first I thought my camera was limited to 59″ exposures, but it turned out that the Zoom control on top of the camera could be used to jump from seconds to minutes (and even hours, but I doubt the battery will provide enough power for that).
Back to our ISS picture…. if you expose for, say, two or three minutes, the stars will start to streak, due to the polar rotation of the planet we live on:
That’s Cassiopeia and Cepheus. You can clearly see that Polaris on the top left does not streak. I took this photo also with my CHDK modded Canon PowerShot. But for my ISS photo I didn’t want the streaks, so I first polar aligned my NexStar 5SE, synced it to Albireo in the constellation Cygnus (always a nice double star to watch) and then taped my Canon PowerShot on top of the telescope with duck tape! This way the Canon would follow the Earth’s rotation during the ISS pass. It worked quite nicely, because the stars in Cygnus are still stars and not streaks. I used the M (Manual) settings of the camera to augment the CHDK 2 minute long exposure. The way this works is that even though the M exposure setting is at 1″, the camera will be overridden by CHDK and expose for two minutes. I used ISO 200, F8.0 (enough light enters the ccd chip during an average long exposure, and a small aperture like F8.0 will yield a longer depth of field), 2 second self timer (to avoid camera shake), manual focus (MF) to infinity. Then it was a matter of waiting for the ISS, but Sputnik on my iPhone had it right on the second. The ISS left Earth shadow at 02:32:19 in the middle of Cygnus.