Adding a GPC would probably defeat the purpose of being at 420mm in FL. lol
(I don't have a large ........short scope........ just the 60ED).
you cant cut the tube as you are working with the distance from the reducer..........that wouldn't change.
if you are at the M84 thread on the reducer the max you have is 99mm to make up........to the focal plane.
I have played this game. Took my 102 F/7 triplet with a removable binoviewer section, removed the extension and tried various placement and combinations of 0.5x focal reducers to get maximum focal reduction that could reach focus and have a usable view. Actually worked somewhat well I got it to operate at ~240mm. Problem is: image wasn't great across the field (field curvature, deformed shapes at edge, etc.), but it worked. TSFlat2 cleaned it up a bit (just don't ask how all this get-up star tested!)
Benefit of doing this playing around was I found a way to use a combination of 0.5x reducer with my Quark to give me fill disc solar. Used that set-up for about a month or so but then just punted on the crazy set-up and just went with a 80 F/6 small apo to do the job right.
But I was using the cheap 0.5x reducers. If you have good quality reducers and using in design range could work very well provided you have correct backfocus (that is what i do with my C11 Edge and 0.7xreducer, provides great 2" eyepiece views and with 146mm backfocus has enough for a diagonal).
Edit: I found the thread: https://www.cloudyni...using-reducers/
Post #17 is my results summary
Edited by ABQJeff, 24 July 2024 - 01:30 AM.