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Check this out: http://www.astropix.com/HTML/SHOW_DIG/027.HTM All the details of how this was done with a standard DSLR & telephoto lens are right there. They did use an auto-guided equatorial mount for this.

Here's an article from a great amateur astrophotographer (who uses both film and digital) on deep sky imaging with digital sensors: http://www.astropix.com/HTML/I_ASTROP/SIGNAL.HTM

Interesting, I like how the rollover effect was done. With the multiple exposures I'm wondering if you can't get the same results with film. Though my 35mm is a cheap one I can still take multiple exposures on the same frame. I suppose what I could do is test it, take a 5 minute exposure on one frame then take 5 one minutes exposures on the next. I don't know anyplace around here that doesn't have light pollution, however there's a waterfall not far where I want to get some tyme lapse photos of early in the morning. I'll need to get at least one ND filter first though.

Oh, I also don't want to leave the impression I don't like or have something against DSLRs, I don't and I'd like to get one myself. Perhaps the Canon 5D. The film camera I have is a Canon EOS Rebel so I'll be able to use the same lenses on both. However before I get a DSLR I want to get a a medium format camera first, perhap one of Mamiya's 645s with a film back. Eventually when the prices come down and I can afford one I can get a digital back for it. My dream camera would allow me to shoot both digital and film at the same tyme. Technically though I don't know if one can be made yet have good image quality, either the light would have to be split with one going to the film plane and the other to the sensor, or possibly have the film right in front of the sensor. The first one though means splitting light in half requiring twice as long an exposure, and the second means the film will interfere with the sensor.

I'm not saying digital beats film in all areas. For long exposures where you can't stack multiple short exposures, film wins, every time. Light painting a canyon is one of those. Single exposure star trails is another.

BUT, astrophotography of deep space objects is different (so is astrophotography of planets, but for a different reason). Yes, if you use a digital sensor the same way as you do a piece of film for astrophotography the film will win. However, the sensitivity of the digital sensor lets you make a series of much shorter exposures.

Suppose your digital sensor is six times as sensitive as your film. Suppose the object you want to shoot requires a one minute exposure to detect reasonably, on film. That same target takes ten seconds to register on a digital sensor. Yes, it's obscured by noise on the digital sensor. So you spend the rest of the minute taking five more exposures (total of six) with your digital camera and average them. You also neglect to take your lens cap off for an seventh exposure, called a dark frame.

You use the dark frame to subtract thermal and pattern "noise" (not really noise, it's predictable so it's a signal, but an unwanted one) from your six other frames. Then you average those six frames. Averaging reduces noise by a factor of sqrt(N), in this case sqrt(6). The link at the end of this post suggests stacking increases signal by that amount, which is a reasonable interpretation if you sum the exposures instead of averaging them.

So now you have a composite digital image that has the same total exposure time as your film image, similar signal level and similar noise characteristics. The difference is, the film shot is one single minute long exposure while the digital image only requires the shutter to be open for ten seconds at a time. If you made those exposures with a lens less than about 50mm the digital exposure could have been made on a regular tripod, while the film picture would have required a pretty good tracking setup. If you were using a small telescope the digital shot would need only a moderately good tracking mount while the film shot would have probably required a very well calibrated tracking mount and guiding.

In deep space astrophotography you can make the same exposures with film and digital, but digital requires a lot less tracking precision because the exposures are shorter. Tracking precision takes money, expertise and patience. When you don't have one of those items, or any of them, digital opens up much more of the sky to your camera than film does.

Planetary astrophotography is a bit different. Generally you've got lots of signal... the easy to image planets and moons are pretty bright. But you want to resolve small details, which means high magnifications. At high magnifications distortions caused by the atmosphere come into play. With a single long (we're talking seconds long now, not minutes) exposure all those distortions add up to smear out your image. With a digital sensor making many short exposures you can realign shots that are shifted and throw out ones that are blurred. There was an article on Slashdot last week about doing exactly that - it's called lucky imaging: http://science.slashdot.org/article.pl?sid=07/09/03/2257224

Cooling a ccd is popular among hard core astrophotographers. It's a useful technique that reduces noise. It makes your imaging more efficient, ie you need to stack fewer frames, saving you time. It doesn't really make it possible to image any deep space objects that you couldn't otherwise though.

Here's an article from a great amateur astrophotographer (who uses both film and digital) on deep sky imaging with digital sensors: http://www.astropix.com/HTML/I_ASTROP/SIGNAL.HTM

The only shot I could find that roughly corresponds in both his film and digital galleries that both have exposure data is the Milky Way

Even better, Jerry's picks are worth looking at, too:
http://www.astropix.com/wp/2006/12/29/top-25-astro nomical-images-of-2006/

Hypering film requires a mixture of hydrogen and nitrogen to be pendantic about it:

http://www.astropix.com/HTML/I_ASTROP/I09/I09.HTM

Quite an art to get it right too.

A.C.

After the recent Leonid meteor showers my interest in astronomy became rekindled and I took the old telescope out of the closet and started pointing it at various things in the sky. Then, I wanted to take some pictures of what I saw so I took apart by webcam and attached it to the telescope in place of the eyepiece. Voila! It worked and I got some great pictures of the moon and some rather blurry shots of Jupiter and a few of it's moons.

Recently I've seen a few pages like this one. That describe how to take pictures of meteor showers with a 35mm camera (by exposing the film for extended periods of time). Is there any way to extend the exposure time like this with a digital camera? Any objects that are dimmer than a planet or a moon don't seem to show up.

I'd really like to set something up to get some shots of the Geminids by aiming the scope at a piece of sky and waiting for one to pass in front of it (or set it up to take repeated timed exposures). Is any of this possible with a Creative Video Blaster Webcam? Or should I fall back to the 35mm camera?