Wednesday, September 30, 2009

Astrophotography for the Rest of Us

A couple of decades ago, when I was still using a fully manual SLR film camera, I tried some simple astrophotography: Long-exposure photos of star trails from a fixed tripod, and also some “piggyback” photos with the camera mounted on a small motor-driven telescope to track the stars. The results were satisfying but hardly spectacular, and the time required was substantial enough that my priorities soon turned elsewhere.

Then last January, at the start of the International Year of Astronomy, my interest in astrophotography began to return. By then I was using a marvelous little Canon point-and-shoot digital camera, and I was delighted to learn that it would take time exposures as long as 15 seconds. While spending the New Year’s holiday in remote Boulder, Utah (about as far from city lights as you can get in the contiguous 48 states), I decided to brave the cold and try a few shots of the winter constellations.

To my astonishment, that little camera recorded 10 times as many stars as my eye could see. Unfortunately, the photos were also plagued by digital noise that severely limited the aesthetic possibilities. I suppose this noise is the digital equivalent of the grainy appearance of photos on high-speed film.

Meanwhile, I had been marveling at the ever-better scenic night photos posted on NASA’s Astronomy Picture of the Day site. Following the links from some of my favorites, I discovered sites like TWAN and The Sky In Motion. These photographers were using digital SLR cameras to make stunning photos showing the sky in great detail behind interesting foreground scenes. The noise levels were acceptable, because DSLR cameras have bigger and better electronic sensors than my point-and-shoot.

A terrific resource for would-be astrophotographers is Jerry Lodriguss’s web site, Catching the Light. One of his technical articles indicates that even some of the cheapest consumer-model DSLR’s can produce excellent night shots. But did I want to spend even $500 for such a special-purpose toy? “Well,” I rationalized, “I’ve already had two astronomy students use DSLR cameras for their observing projects, and I need to learn how to help them when necessary.”

I got the new camera on September 10. Then even I, a professional geek, had to spend a week just getting familiar with all the buttons and menus. I also discovered that to shoot exposures longer than 30 seconds (without a computer connected), I needed to get a $25 remote switch. Finally prepared, I headed up to Ogden’s foothills on a couple of our recent spectacular September nights. The best shots from these sessions are posted here. In short, I'm amazed at what can now be done with amateur equipment and very little effort.

Incidentally, this was the first time I’ve ever been glad for light pollution. Although scattered light from the city brightened the sky (and pretty much ruined any shots facing west), that same light pollution cast beautiful illumination on Ogden’s mountains.

How much further I’ll take this hobby, I have no idea. Certainly I’ll try some photos from a few other sites around Ogden. And I’ll bring the new camera on camping trips, to see what it can do from some darker locations. Perhaps I’ll try to schedule these trips to coincide with favorable moonlight to illuminate the scenery.

But I’m not a professional photographer, so if you want to see really nice photos of the sky, follow the links above.


  1. you make it sound as if only a digital camera makes this possible, dan --- is this the case? Or do digital cameras just make the follow-up process easier? ctrentelman, film fotografer

  2. Hi Charlie,

    Depends on what you mean by "this".

    For long exposures of star trails, a manual film camera is still better because you don't have to worry about battery life. But if you don't want the stars to trail and the Milky Way to blur, you have to limit exposure times to about 15-30 seconds (with a wide-angle lens--otherwise even shorter) and therefore you have to use high ISO. I've never tried films faster than Ektachrome 400 so I really don't know what kind of results you'd get with, say, ISO 1600 print film. It would be easy enough to try, and perhaps I should. My impression, though, is that the professional scenic night photographers have all gone digital.

    Of course another big advantage of film is that you can get an old manual 35mm film camera with a fast wide-angle lens pretty cheap these days, I should think.

    If I can find the time, I'll try to post some of my scanned slides from two decades ago.

    The reason I bought the DSLR was partly because I knew (from others' experience) that it would produce good results, and partly for convenience, and partly because I wanted to learn to use such a camera so I could help students who have them. Another thing you can do with a DSLR is computer-controlled sequences of hundreds of shots to make time-lapse movies. I haven't tried that yet but I intend to.

    There's a great comparison of film vs. digital here, though it doesn't discuss night photography. Professional astronomers went digital back in the 1970's, and have always been in the forefront of digital sensor development. For a comparison aimed at serious amateur astronomers (which I am not), click here.

    The title of my article, remember, is Astrophotography for the Rest of Us. As Ken Rockwell says, most people will get better results with digital. That's especially true of night shots where a beginner can easily waste several rolls of film before getting any decent images at all. For beginners, the immediate results of digital are an all-important factor.

  3. Hey Dan!

    I've been looking into this for about a month now. I'd been shooting photos with my point and shoot, but wanted to be able to do longer exposures. I was inspired to start by investigation about constructing a tangent arm drive, and discovered some commercial ones (like the one from AstroTrac). So now I've been researching DSLR cameras -- what did you settle on?

    -- Shane

  4. Hi Shane,

    I got the cheapest Canon, the Rebel XS. So far I have only the kit lens, 18-55 mm f3.5. (Multiply focal length by 1.6 to compare field of view to 35mm film or full-frame digital.) From Lodriguss's descriptions I don't see much advantage in going to a more expensive 1.6x DSLR, so the next serious step up would be a full-frame DSLR which would cost a few thousand. Even then, I think the only significant advantage would be field of view. If I decide to invest more, my next purchase will probably be a faster wide-angle lens. Of course, if your camera is going to track the stars, you don't need a particularly fast lens because you can just use longer exposures. The downside is that you then blur any foreground scene.

    Be sure to read what Lodriguss says about the standard built-in filters that block most of H-alpha. If emission nebulae are your thing you'll want to modify the camera to remove this filter, and that'll create headaches during daytime use. One more reason to just use film if you're on a budget.

  5. Hi Dan,

    Nice blog you have going here! I have had some success using a Canon Digital Rebel DSLR both on the telescope and by itself (but attached to the telescope mount to utilize the drive motor). To help reduce some of the noise, I stack many subframes. In fact, the software program I use lets me set up a custom shutter control routine along with processing of the subframes into a final composite image. I still have a long way to go to catch up with the likes of Jerry Lodriguss and others, but I'm still amazed with my results through the Digital Rebel!

    By the way, very nice photos of the constellations over Ogden’s mountains!! Ray Shore

  6. Hi Ray, thanks for your comment. I just found your web gallery and looked through some of the nice images there. It's always interesting to see what can be done with certain specific equipment and techniques. Are you using an unmodified DSLR (with factory filter in place which removes most of H-alpha)?

    Even though I'm a geek who would enjoy stacking subframes, my main interest for the time being is in shots that include foreground scenery--so this technique isn't really an option. Maybe in a few months I'll have some better shots to post here...

  7. Hi Dan,

    Yes, my DSLR is unmodified. I wanted it to be universal for normal terrestrial photography.

    I like your type of imaging with scenery in the foreground. You have created some beautiful shots! I'll have to check back later to see some of your other work. Ray Shore


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