Quote:
Originally Posted by rumples riot
You can buy derotators from a number of different sources (at affordable prices) and use this to gain perfectly acceptable images. With practice fine work can be done. Afterall, large observatories have been doing this for some time now.
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I'm going to chime in here. I don't know if you've ever use a field de-rotator. They sound attractive, but from my experience the amateur versions are not accurate enough at anything over 1200mm focal length. I used the Meade #1220 for approx 6 months before selling it for half the price I bought it for (had no takers). It was a complete waste of time. If you're carrying a reasonable payload, you also need to watch out for flexure. I have not had the pleasure of using the Pyxis 2" or 3" camera rotator. These are commonly used for remote operation of object compositing/framing, but can also be configured to de-rotate fields. These are considerably different beasts to those used by large professional observatories such as this -
http://www.ee.nmt.edu/~teare/fielddr.htm. You could certainly buy one of these professional units, but for the price of two 20" SDM scopes and then some.
Alternatively, you could image using CCD drift scanning techniques, but this is sub optimal for small FOVs. The level of nebulosity collected is based on the time it takes for the object to drift across the CCD registers and is read out. Thus, obtaining those faint wisps or globs become difficult as exposure time is constant.
I'm all ears to see where this debate is going. The cost per inch of aperture with large newts/dobs (14" and up) is appealing. Great visual instruments and for planetary images. However, until we start talking large dobs/newts on GEMs or Eq. fork mounts, I'm going to tune out. We all know that there is no substitute to long exposures when it comes to DSO imaging. To date, long exposures for DSOs are only practical through the use a GEMs or Eq. fork mount. I'm not convinced that a Eq dob platform (i.e a wedge) provides sufficient tracking accuracy (especially at the focal lengths discussed here).
So to this end, the "ultimate" scope does not exist. We all wish it did and some may come close. The old "horses for courses" statement applies. A superb visual instrument doesn't always apply itself well for photographic work (and vice-versa). You need to make an informed decision as to what features/aspects are important to you - there will be compromises. I guess if there is such a thing as the "ultimate" scope, it would be one that offers you the most pleasure and assists you in achieving your astronomy goals - whatever that maybe.