Saturday, July 16, 2011
The Basics of Astrophotography
If you are reading this article, there is a very good possibility that you are interested in learning more about astrophotography. Perhaps you own a camera like the one pictured above and believe that you would like to try your hand at taking some sky shots. Good. This is how it begins. And how far you go with it is up to you and your budget.
You will need a tripod and a remote timer or cable release for an older 35mm SLR. At the very minimum, you need a means of keeping the camera stationary, and a means for tripping the shutter. The adjustable alt-az head may be nice for framing but is completely optional. With this setup, you can do about a 30 second exposure with fast film or high ISO settings and achieve some interesting results. This is the least expensive and least intrusive means of getting into astrophotography. In many ways it is also the most fun because at no point will you invest less energy and achieve greater satisfaction than when beginning at this point. The problem is, most guys get hooked at this point and they want to get up to the next level. You can do this fairly inexpensively, providing you have a telescope on a tracking mount and a means to mount your camera on the tube.
This image shows my old trusty Minolta X-370 astrophotography 35mm SLR mounted on a special rail I had made for my telescope cradle. The nice thing about piggybacking is that with short focal length lenses like the 50mm f/2, and even fairly decent polar alignment, you can achieve some very spectacular results because you can now increase your exposure times from over 30 seconds to perhaps 30 minutes or more, depending on your sky conditions. I have always enjoyed this type of astrophotgraphy because it requires minimal intervention and delivers excellent results in a consistent way. You can substitute a DSLR in place of this camera and do about the same thing, taking a number of successive shots and later stacking the images with Deep Sky Stacker to achieve a very long exposure time equivalent. Digital technology is superior to the old film in that if you get a bad frame from something like a jet or a satellite you can simply leave the frame out, not so with the old methods.
If you don't own a DSLR, a cheap way to get into imaging is with something like the Meade Lunar and Planetary Imager, the LPI. The LPI and a laptop allows you to shoot images of the moon and planets. This webcam device can deliver many hours of enjoyment and will allow you to begin to use software for capture and control of your equipment. At this stage you will want a good equitorial mount with the ability to track sky objects, and a barlow lens or two to achieve a better image scale. The degree of difficulty is higher than with piggyback work simply because focus becomes more critical as does the ability of the mount to carry the load and track properly.
By this point you are very interested in doing this astrophotgraphy thing. In the days before autoguiders and digital cameras, a setup like the one pictured could let you couple your camera to your telescope and guide the stars with a fairly high precision manually, at least good enough for film. Doing this with today's technology is even more interesting.
First you will need a T ring and T adapter. This allows you to couple your camera to the focuser on your telescope. You will need a means to control your camera. You can do this with a remote timer, or even with software like BackyardEOS, which is what I am now using. And you will need a means of guiding. Guiding is a process of making minute corrections in your tracking that are sufficient for your image scale to make images appear pinpoint without egg shaped stars. More often than not, this is being done with autoguiding, a means whereby a second camera is being used in conjunction with a software package like PHD Guiding.
This final image shows a setup similar to this mentioned, where the camera lens is now the telescope. This is called prime focus. You can see the guide camera and guide scope on the right, and the camera coupled along with a T ring and T adapter to the focuser. Beyond this you may wish to place specialized imaging cameras at prime focus to do even more precise work, but be warned, by the time you get to this stage your investment will be considerable and your knowledge will be very extensive. Many make the mistake of beginning at this stage, and although they eventually get fairly good at it, they find the curve to get there pretty steep. Plus I just think you miss out on a lot of the joy of what this is all about if you don't go through the steps first. Hopefully this article will help someone out there to be inspired to become the world's next astrophotographer.