question about equipment?

John,

I have been dabbling in astro-photography now since about 1982, starting with an Olympus OM1n and continuing with that camera and various Olympus lenses from 24 mm up to 500 mm until surplanted by DSLR camera equipment in about 2004. I now use, primarily a Canon 60D. Fortunately with an adapter I am still able to use much of my collection of Olympus Zuiko lenses on the Canon 60D (or 20D and 20DA bodies. While I do have to manually focus and manually adjust other settings, you have to do that anyway for astro-photography. I also have a Tamron 90 mm f/2.5 lens which is particularly good for astrophotography as it exhibits very little chromatic aberration as it has ED elements.

With the setup above much of my photographic efforts have bee utilizing what we call "piggy-back" photography. If unfamiliar with the term it means that the camera and lens, or camera mounted to a smaller telescope is mounted "piggy-back" on a larger telescope. You need a rigid attachment so the camera with lens has no possibility of shifting it's position relative to the larger telescope which you use for manually guiding or auto-guiding the exposure.

Back in the old film days I found that EktaChrome 200 was a very good film to use for astrophotography as it had a good reciprocity profile (it keep delivering to a degree over time). I also dabbled with higher ISO films up to 1600 speeds, but there were trade-offs including color shift and graininess. Even so, and even using relatively fast camera lens or telescope f/ratios of F/2.8 up to about f/5.6 the exposure times with film were long - at least 10 minutes and sometimes up to an hour for an individual frame. Now this is all from a dark sky site where you can see the Milky Way visually without optical aid. Forget most astro-photography from the city with longish single frame exposures, there is just too much light pollution and your exposures will be washed out. The exception being when specialized filters are used and/or with the stacking of much shorter exposures. In addition planetary, lunar and solar photography are not affected by light pollution or daylight (duh! - went you photograph the Sun you are looking right into daylight).

All of the astro-photography that I do and that most do are done with the assumption that the exposure is guided. As planetary, lunar and solar photography attempts are pretty much all short-exposure attempts, typically sub 1 second exposures, a guided mount is not needed in most cases. You can also get by with relatively short 20 second or less shots of the night sky with wide angle lenses such as 10 mm to 28 mm in my experience, with the lenses wide open. Blowing them up will show some trailing, but without additional magnification they are ok (still not as good as guided). Your image scale will be too small for many objects but for the big picture such as whole constellations and broad swaths of the Milky Way, the results can be quite good. I did some of this at the recent trial run that we did at "White Horse", the site for our upcoming 36th Annual Deep South Star Gaze and the results well illustrate how good this site is for what we do. Most of my exposures were about 20 seconds or so long at ISO 1600.

For longer exposures and drilling in for more detail on individual deep sky targets you need longer focal length equipment. About 4 year ago I bought an ExploreScientific "Essentials Series" 80 mm f/6 refractor. It has a 480 mm focal length. I usually photograph thru it using a TeleVue 0.8x reducer/corrector which alters the scope down to a focal length of 384 mm @ f/4.8. It yields great results with 2 to 3 minute guided exposures. Typically this scope is mounted on the back of some of my larger refractors.

Many people are now using CCD imagers and they "auto-guide" exposures. I guess I am "old-school" but basically I just do not find that I have the time or energy to invest both time and money into new equipment and techniques. Our skies also do not usually warrant the investment in both. I have found that some of the results that I get with manually guiding single exposure shots are pretty good, so I will likely continue doing it the way I do it with the satisfaction of knowing that I have the ability to push up to the limit of how I am doing astro-photography and with what equipment I have.

The pictures above were taken by me in west Texas using the ES 80 with reducer, mounted on top of a larger scope which was used as a guider.  Both exposures are about 3 minutes each.  What you see are the Andromeda Galaxy and the North American Nebula.  First priority being dark skies.  Click on each for a larger view.


Barry Simon