Astrophotography

By Dean Ketelsen, Member

Getting Started

It really is easy to get started!  All you need is…

    • A camera capable of taking a time exposure, preferably with a “fast” lens.
    • Film.
    • A tripod, the sturdier the better.
    • A few accessories — a shutter release, a flashlight (astronomer’s red preferred), and a notepad.

That is it… and most of you are likely well equipped!

Equipment

Camera

Best is a manual camera which does not need batteries to operate the shutter. Many electronic cameras drain battery power during long exposures. If you use one, bring spare batteries! You can do astro pictures with nearly any camera so long as it does “B” or “T” time exposures. Most any name-brand 35mm camera will work well for you.

Lens

For starting out, normal, wide angle or slight telephoto lenses are best. Single focal length lenses are preferred rather than “slower” zoom lenses. Longer telephotos and zooms can be used for shorter exposures of moon/planet conjunctions.

F/stops explained: An F/2 lens’s focal length is twice the aperture. An F/4 lens’s focal length is 4 times the aperture. For an 80 mm lens, the effective aperture at F/2 is 40mm, for F/4 it would be 20mm. An F/2 lens is “faster” than an F/4 lens. Think of it as finishing the exposure faster! To help calculate exposures, a “stop” is defined as a factor of 2 increase or decrease in the amount of light. Because the area of an aperture goes as the square, an F/2 lens passes 4 times the light of an F/4 lens, so is 2 stops faster! A normal lens may be F/2 or F/1.4. Lenses used by professionals may be F/1.2 for low light levels. Regardless of their maximum aperture, most lenses perform better stopped down a bit. Experiment to see where your lenses perform best.

Film

You have an incredible selection of film compared to just a decade ago. Today there are several films that really are perfect for astronomical applications. Film sensitivity is high and grain and resolution is very fine. Reciprocity is a loss of film speed for long exposures. In other words, you double the exposure and the film density does not double. Fortunately, with today’s films you need not worry about reciprocity very much. Just realize it does affect some film, thus is a factor is picking your favorite. Hypersensitizing (hypering) is a film treatment that increases films sensitivity and reduces reciprocity effects. A kit to do it yourself is expensive, but you can buy treated film for less than twice the normal cost and that is the way to go as you start out. Unfortunately, the hypered film you buy has a limited life – color film lasts weeks to months, but B&W lasts up to a year in the freezer. Spectral sensitivity is also a concern. Many nebulae in the night sky are red from hydrogen emission. However some films are very insensitive at those wavelengths. A red-sensitive film is another factor.

Film Recommendations: For black and white photography, the ultimate film is Kodak Tech Pan. It has just about the finest grain available, has excellent red sensitivity and when hypered is quite sensitive. Unfortunately, it is a real dud unhypered. For the highest contrast, this film needs to be developed in D-19 developer. However, I have not found a lab that does that, so you need to process your own film, which is no problem for B&W. This film exposed thru a red filter does AMAZING work on hydrogen clouds in our galaxy.

For color negative film (prints), the choice is less clear than for B&W. A couple years ago, the choice was Kodak’s PPF400, but it was discontinued. Shortly afterwards, Kodak came up with PJ400, but it too was dropped, though there are rumors that the special order film LE400 (for law enforcement) is the same film. Kodak is recommending Supra400 as a replacement. APML (Astro Photo Mailing List) amateurs are using up their stocks of the above, but some preliminary tests show Supra 400 as a good choice.

For slide films, again, the choice is very clear. Kodak’s Elite 200 Ektachrome is a great choice with good sensitivity, fine grain, good red response and a neutral background. It does not need hypering and is readily available at Walgreen’s on your way out of town for an observing session! This is my film of choice with the public slide presentations that I do, and the film that you are about to see projected. The only thing out of the ordinary that I do is have it pushed 1 stop when I get it processed. The reason I do that is that it increases the contrast very slightly, and does not seem to increase the grain size.

Processing

While B&W film is easy to process, color chemistry has tight temperature tolerances and chemicals don’t last long enough to make it worthwhile. Most any lab will develop your color films, but there are things to watch out for. Many will see your dark slide as unexposed and will likely not mount them or worse, cut and mount them incorrectly. Your color negatives may look like they have dust specs to the technician and they may not get printed. Also, even if they are well-exposed, the exposure computer may introduce color shifts and improper exposures from what you might expect. A good lab is a real treasure. My favorite [in Tucson] is Photographic Works on Grant near Dodge. They develop and mount slides in 3 hours and follow directions well and enough professionals and astrophotographers use them that they know what they are doing.

Tripods

The sturdier the better. Make sure that you can point them upwards without the handle hitting other parts of the tripod. Taller ones make it easier to look through when composing. Like telescope mountings, a stiff sturdy mount makes use of the camera that much easier and more efficient.

Cable Release

The ones that you can lock with one hand is great as it frees up your other hand for starting the timer.