I have read quite a bit of literature here about the nifty Celestron C90 Orange Tube and the proverbial "hen's teeth" original LAR.
Well, I pulled the trigger on a mint condition C90 Orange Tube recently that managed to come with an original LAR and Celestron 93653-A 1.25-Inch Visual Back (made in Japan version).
When it comes to diagonals, do you folks (especially those with actual experience owning the C90 Orange Tube) recommend investing in a good quality 2-inch SCT diagonal (e.g. a GSO Quartz 99%) to screw onto the LAR directly or investing in a good quality 1.25-Inch diagonal (e.g. a dielectric) to screw onto the Visual Back?
I plan to only use 1.25-inch eye pieces so perhaps a 2-inch SCT diagonal is overkill (I found a picture on the internet of someone using this setup with a 2-inch eye piece and though it would be fun to give it a try since I do have the original LAR). Also, has anyone been able to use a 2-inch SCT diagonal with the C90 and get 1.25-inch eye pieces to focus properly? I read about issues with focusing the C90 with using modern diagonals and eye pieces over the original 0.965-inch accessories.
Another thought I have is to use the Orion 90-Degree Correct-Image diagonal with the Visual Back, but I am not sure about how the optical quality would stack up against a 1.25-inch dielectric or a 2-inch GSO Quartz 99%. There is basically only 1 model of the 90-degree correct-image diagonal (handy for terrestrial use), so no choices there in terms of upgrades.
Also, for those who have tried a hybrid diagonal versus either a 1.25-inch diagonal screwed into the Visual Back or a 2-inch SCT diagonal (probably rare) screwed into the LAR directly, do you actually notice any optical improvements when using 1.25-inch eye pieces? The 0.965-inch hole is the bottleneck here and I am not sure exactly how much of an optical improvement one can really squeeze out of this little orange tube.
Thanks in advance!
Edited by topgun0728, 29 April 2021 - 06:05 PM.