webspotting 15 - exposure advice

As published in the Apr/May 2010 issue of SCOPE, the newsletter of the RASC Toronto Centre. Republished here with permission.

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One of the most common questions asked by people starting out in amateur astronomy is: How do I take pictures?!

You have a telescope (or are about to buy one), you have a good little camera, why not use 'em together, right?

The response from experienced astronomers is interesting. Or should I say surprising: Don't!

This may sound severe and discouraging but there's a method to our madness, of course, or so we believe (I hope). Astrophotography is one of the most challenging things to do. The occultationists would argue this point till the Sun comes up but we all agree that there are special skills required, a high degree of telescope and camera knowledge, and Murphy's Law, which tends to be a factor. So experience and perseverance in large quantities are needed also.

Our reasoning is simple enough. We don’t want people starting out to get discouraged. And we want to, as gently as possible, alter expectations. Someone just starting out should not expect to immediately produce work like those made by the Hubble Space Telescope. With time, effort, and money (of course), spectacular results can be achieved. All that said, there is a form of astrophotography that is relatively simple and easy to do with the potential for very good results, particularly if your target is the Moon or a bright planet.

There are different forms of astrophotography, like prime focus and wide field guided, and different cameras, such as CCD and DSLR. Discussing all of this is well beyond the scope of this column. But, arguably, afocal shots with a Point-and-Shoot are the easiest form of photos to make.

Briefly, afocal or projection photography refers to positioning your camera near the eyepiece, where your eyeball would normally be, and snapping away. Sounds simple, right? Are you sitting down?

Equatorial mounts, RA motor drives, polar alignment, good eyepieces (cleaned of course), appropriate exposure and/or aperture control, ISO control, appropriate optical zooming with the camera, optical alignment (in 3 dimensions), camera stability, touchless shutter release, wind, dew... you have to worry about all these things! Perhaps the most challenging is appropriate focus. The gotcha? You don't focus the telescope for your eye (which produces converging rays of light); you have to focus for the camera (with parallel rays)!

I recently found a good little web page that covered these items concisely and clearly, all the while reducing intimidation.

http://www.saao.ac.za/~wpk/exposure.html

So, fire up the 'scope, choose an eyepiece, choose a target (start with an easy one like the Moon), look up your exposure and ISO numbers, focus, mount your camera (if possible), and start shooting!

Good luck. Let us know how you do.