F 6.3 or F 3.3?

Brian,

I should also add that the f/3.3 will produce vignetting and it will be an issue if your imaging chip is sufficiently large. Such a reducer is only suitable for small imaging chips since they do not cover enough of the available field to include the vignetting.

Using the SBIG CCD cameras as an example, you would be fine with the ST-7 line but not with any of the rest (ST-8, -9, -10, -2000 etc). Ditto with the recent lines of digital cameras and their large chips.

Anthony.

Jeff I looked up Ian King Imaging www.iankingimaging.com/show_products.php?category=17 and I found what you were on about (second product down).It said that newtonians would not be able to achieve focus with it, any suggestions :

Brian --

Newts are usually reasonably fast to start with, so there aren't a lot of focal reducers made for them. They also tend to have the shortest focusing ranges (in order to keep the secondary mirrors as small as possible), which exacerbates the problem.

I'm not convinced the Atik won't work with the DSI, though. When you put your DSI in normally, where is the correct focus? Is your focuser draw tube well extended, or is it in almost all the way?

It would be a pain, but you can also get more in-focus in a Newt by extending the collimation screws out farther. Of course, then you have to re-collimate every time you add or remove the focal reducer, which can get tiring.

-- Jeff.