The Pentax SDUF-II is specifically made for imaging. It is extremely sharp across the field, and nicely flat in illumination. I would rate it with the best of the wide-field astrographs. At f/4, it is a little wider and a little faster than the alternatives.
I have been testing it for review, and need to sell it so I can move on to testing the next scope. Otherwise, this would be a keeper! Here's why I like it:
* It is the easiest scope to focus manually that I have used. It has an oversized helical focuser with a Vernier scale. You can make exceptionally small yet accurate adjustments for focusing. This is of course critical for successful imaging at the fast focal ratio of f/4. It is the only scope, in fact, where I have not felt frustrated trying to focus manually. The key is the ability to make precise adjustments to focus position without guesswork because of the built-in scale marks.
* Back focus is quite long, long enough to use a motorized automated focuser if you want to go that way. There is no problem fitting motorized focusers, filter wheels, or other accessories into the image train.
* Image quality is very high. Contact me to see images taken with this scope.
* At 400mm, it has a _very_ wide field of view for both film and CCD. The image of the Witchhead below is an example of how you can use this scope to take wide-field images with CCD that are normally reserved for film.
The SDUF-II, like other Pentax scopes, is not readily available in the US, so they are not very easy to come by. A number of imagers are using this scope; contact me privately and I will send you some links to web sites that show what can be done with this scope.
Will sell for $2600, including scope, 2" back, dual 1.25"/0.965" back, hard case, lens cap. The scope is in superb condition. The image of the Witch Head Nebula below was taken with a Finger Lakes CM-10ME camera. The field of view is more than 1.5 x 2 degrees.