Wide-Field Astrophotography Equipment

(Keep in mind that these pages were originally written many years ago before the beginning of the digital camera revolution. However, understand that film cameras are still the equipment of choice for this type of astrophotography when it comes down to a quality vs. price analysis. Also, much of this information still applies to digital cameras.)

A very basic set-up might be comprised of a 35mm SLR camera with a "normal" lens and the ability to lock the shutter open (a "B" setting and a locking cable release), and a tripod. Even without a way to track the stars, this is still a useful beginner set-up.

Cameras

Generally, the simpler the better. Auto-focus and all those fancy electronics that a $500-1000 body has won't do you any good for astrophotography. The ideal camera body is one which is completely mechanical. Cold weather saps a camera battery like nothing else, and most cameras require battery power to hold the shutter open. Thus, if you can get a hold of a camera with a completely mechanical shutter you will be very happy. But, try what you have first and see if it is suitable. The battery problem won't be a problem if you live in a warm climate. If you will be shooting in sub-freezing weather with a non-mechanical camera, carry a second set of batteries in a warm clothing pocket.

Lenses

Focal ratio

Aperture, aperture, aperture! Ideally, you want the biggest piece of glass at a given focal length that you can find and/or afford. Unless you have a very good tracking system, you will rarely want to shoot slower than f/4, except when shooting point sources with long lenses. Fortunately, the "normal" lens that comes with a camera (in the range 45mm to 58mm) is almost always f/2 or faster. However, very short focal length and telephoto lenses tend to be slower than normal lenses. Once you get to 300mm or longer, it's tough to find a good lens faster than f/4 and if you can find it, you may have to pay an arm and a leg for it. Generally, you should stop the lens down one stop when you shoot because there's nothing like bright point sources to reveal coma, spherical aberration, chromatic aberration, and all those other dirty words. Astrophotography is easily the most demanding form of photography in terms of optical quality that a civilian is likely to attempt. Exceptions can be made if you have a very high quality lens, or if your target only fills the very center of the frame, or if you are shooting a very faint object and can't afford to block half of the photons that pass through the front of the lens. See the calculations page for some sense of how focal ratio affects exposure times.

Focal length

As suggested in the previous section, anything with a focal length less than about 300mm is useful. Thus, 300mm is the maximum focal length I talk about in selecting a lens for a particular target, and I usually limit my discussion to 200mm. The problem is that lenses longer than 200mm are hard to accurately track with simple equipment. There aren't really any limits on the low end of the scale, except that a good ultra-wideangle lens will be expensive. I'll make the note here that an 8" f/1.5 Schmidt camera (an expensive, specialized telescope used exclusively for astrophotography) has a 300mm focal length.

Zoom lenses

If you have a good zoom lens, more power to you. However, these lenses usually aren't very fast (typically f/3.5), and when pointed upward, the barrel can slowly creep downward, which of course is a big problem. Consider duct tape around the barrel if you use one of these for astrophotography.

Tripods

Basically anything will work as long as it's sturdy and doesn't vibrate much. Hanging a weight from the tripod can help the latter a lot. Of course, if you are doing piggyback astrophotography, presumably you have a decent tripod for the telescope and equatorial mount.

Tracking

There are two main options here, piggybacking a camera on a telescope on an equatorial mount, or building a "barndoor" drive. Both can be powered either by a motor or by hand. A third option is a motorized equatorial mount of the sort that people use to "equatorialize" a Dobsonian mount. A piggyback set-up obviously requires that you already have a telescope, but has the advantage in that it's already built. If the equatorial mount is motorized, you may not have to do any adjustments during an exposure, depending upon focal length, length of exposure, and quality of the set-up. With a non-motorized mount, you use the slow-motion controls and the view through the telescope to track. A barndoor drive is more portable and inexpensive, but does require construction. Again, a motorized system requires little effort once you get it working right. A hand powered design requires you to rotate a screw every few seconds by the proper amount. This is very tedious, but you tend to get used to it. Polar alignment becomes very important with longer exposure times and longer lenses. See my barndoor drive page for more info.

My equipment

My primary body has been a Minolta X-7A 35mm SLR, circa 1988, which cost about $170 new. This is a manual camera, except for a built-in exposure meter. Unfortunetly, power is required to hold the shutter open. In mild weather, I've kept the shutter open continuously for as long as an hour. In cold weather (say, below 10F), battery drain can be a big problem with a long sequence of several-minute exposures (i.e. during Hyakutake's close approach). This was my only camera body so it gets used a lot and has held up very well.

I finally bought a Minolta SRT-101 body from the 70s (via the internet several years before eBay existed) with a broken light meter for $50. It's a great old completely mechanical camera that takes the same lenses as my X-7A. The only drawback is that it's built like a tank and weighs about as much.

All of the lenses I currently use were purchased used. The arsenal is: 35mm f/2.8, 50mm f/2, 58mm f/1.4, and 135mm f/2.8. All of these lenses were made by Minolta and are of excellent quality and I paid a total of about $180 for them. I also have a mediocre 28mm f/2.8 and a 28mm-70mm f/3.5 zoom which are rarely used.

I have a good Bogen tripod with a simple tip-tilt head (about $100 in 1988) that has served me well.

Films for wide-field astrophotography

Even though most deep-sky objects are small even with a medium telephoto lens, film requirements for wide-field astrophotography are very similar to those for prime-focus work. Namely, red and blue sensitivity, as fine of grain as possible, and speed, speed, speed. In general, the happy medium occurs at speeds of 400-1000.

I used to have recommendations for specific films, but I've done very little astrophotography during the last several years, and I don't think any of the films I used in the mid-late 1990s exist anymore in the same forms. However, I will say that you should start with 800-speed films from Fuji and Kodak, which are usually pretty good. Buy the refrigerated professional films if you have easy access to a good photo shop, but the off-the-shelf versions generally work quite well, too. Unfortunately, many of improvements made for films that make them better for "normal" photography are to the detriment of astrophotography.


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File last modified: 08 January 2005

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