I haven’t had much time to process the images I took the other night, but I have got one vaguely Martian-looking shot out of the effort. Before we get to that, let me explain what I’m doing.

The June issue of Sky And Telescope had an article on an emerging practice among budget-minded amateur astronomers: using webcams to image bright objects like the moon and planets. Some enterprising folk have even made extensive modifications to these cheap cameras to get them to work for long-exposure, deep-sky targets. The entry point for astronomical digital cameras is about $1,000, and they don’t get good until two or three times that, so having a serviceable option in the $100 range is a good thing.

I am using an old 640×480 IBM webcam that I bought under a compelling rebate offer a year and a half ago for a well-intentioned but ill-fated experiment with videoconferencing at the home office. There are a couple of cameras that have floated to the top in amateur astronomical circles, and this isn’t one of them, but had the advantage of being in my possession. Now, the webcam astronomy scene is most accessible to people who have use of a machine shop, which I just happen to have through the generous services of my father-in-law. One plastic and one aluminum fitting later, and we were seeing light.

The camera’s biggest shortcoming is the lack of manual “shutter speed” control; image gain control is fully automatic, so a bright subject on a dark background (say, Mars) must fill a significant portion of the picture before it will be anything but a completely saturated white blob. This means I had to crank up the magnification as high as my equipment could manage, which in turn resulted in less clarity, not more. (I had a spreadsheet that calculated the effective focal length in this arrangement, but I can’t find it. I think it was something like 8000mm, but I’d have to redo the calculations and measurements to be sure.)

Well-exposed Mars in view, I then captured about five minutes of video, resulting in 436 frames of 640×480, 24-bit video. A scaled-down and shortened snippet of that video can been seen here if you are interested in seeing what it looked like in real time on the laptop screen. The ever-useful Registax then selected the 242 best frames of that shoot, aligned them, and digitally combined them to form this rather unimpressive image:

A little bit of Photoshop histogram maintenance later, and we have:

That, I think, is as good as it’s going to get with my equipment. The blotches on the center-left of the planet are due to dust on the CCD element, which will be blown off with compressed-air impunity this evening. I’ll update this post with some more details, including the name of the prominent dark band on the upper half of the planet, as soon as I have some time to do a bit more research. (No Martian atlas is at hand.)

I’ll also post some lunar shots I took that same night. They should be somewhat sharper.

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• Posted by Tim on Friday, August 15, 2003 at 6:49:19 am PDT
• Category: Miscellany
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