I have a ZWO ASI2 90mm mini (1.25") with a mating 0.5 focal reducer attached at the front end. I would like to get still more focal reduction. Is it possible to attach the Celestron 0.6 focal reducer in front of the NexStar 6SE visual back and then insert the camera/0.5 reducer into the star diagonal so that the 2 focal reducers work together? I'm just not sure of the optics and wonder if anyone has done this? I realize focal reducers can be stacked but I think this means they are touching each other, which would not be the case here.
Celestron 0.6 focal reducer with 0.5 focal reducer
Posted 09 October 2019 - 03:50 PM
All I have ever read is it is NOT a good idea to stack reducers. Optical mess.
Posted 09 October 2019 - 06:19 PM
There are a number of threads in this Forum on using stacked (compound) reducers with small sensors (1/3 inch) like the 290, or 1/2 inch sensors - see this one for example.
My preference - using a 1/2 inch Lodestar X2 - is to stack two f/6.3s and operate at about f/4ish; I find less vignetting using twin stacked f/6.3s, compared to a 1.25inch 0.5x with a f/6.3. If you have a significantly larger sensor, vignetting and aberrations at the edge of the field of view will be more noticeable. Just my 2 cents.
Posted 09 October 2019 - 09:57 PM
I have used 0.63 and 0.5 focal reducers together without much problems with the C9.25. I put the 0.63 reducer at the telescope, then adapter, and use Orion extension tube. Then I put the 0.5 reducer close to the camera. For me, it is around f/2.75 to 2.9. There is going to vignetting and coma, but the trade off is shorter exposures, wider views, and less tracking problems.
Edited by Ptarmigan, 09 October 2019 - 09:57 PM.
Posted 10 October 2019 - 02:59 PM
I have stacked an F/6.3 reducer at the visual back of a C8 with a .5 reducer on the nosepiece of an ASI385, which has a slightly larger sensor than the 290, resulting in approximately F/3.7. I'm not sure but I don't think I used a diagonal for this shot.
It certainly works, but there is noticeable vignetting and depending on the object being viewed, may or may not be acceptable to you.
C8 F3.7 (.63 + .5)
IDAS D1 filter
233*4s 15m total
Edited by chilldaddy, 10 October 2019 - 03:02 PM.