6.3 SCT focal reducer on a refractor?

Anyone every use an adapter such as JMI's # ADPT2THREAD to attach a 6.3
Celestron or Meade SCT focal reducer to a 2" refractor for imaging? I believe the parts would all attach without problem, but would
it reach focus or have issues such as vignetting using a DSLR?

I have not done so.

Just in my brain, though, you have to remember that the SCT focal reducer is meant to not only reduce but also flatten. The SCT image plane is naturally curved, and I do not know if the corrector flattens the plane simply as part of its apparent focal length shortening, or if there is even more correction in it to flatten the field also. In short, unless the inherent curvature of the refractor is essentially the same as the SCT, it may be "flattening" to the wrong dimensions.

Alex

Mark,
I have used a 0.63 SCT reducer on my Megrez II refractor and have several images on my website with this set up. I am pretty satisfied with its flatness, but I do have to process out some secondary spectrum.

Be careful with back focus. I do not use the adapter because I picked up a 0.63 reducer at a swap meet that was machined to a short 2 inch nosepiece - so it fits further in the focuser than it would with the adapter you mention.

Now the Megrez I use is known for it's deep infocus, yet I don't think I can do anything past a 0.5 reduction and still reach focus. I know Steven recommended a CCD back distance of 110 mm, but I believe the FL of the 0.63 reducer is about 230mm and my calculations would put the CCD at about 85 mm back distance.

So I guess the advice here is be prepared to shorten the reducer to CCD distance in order to achieve focus. If you can reach focus on a 0.63 reduction, fine, but you may have to bring in that distance and settle for a 0.66 or 0.72 reductions.