Hi, all. I've seen a few posts on this, but - having had the question and now having answered it - I figured I'd put this up.
I've got an old Meade etx125. It's been de-forked, and remounted on a GEM - which was a process. But I've now replaced the plastic back with one of the Wegat ones, with 2" compatibility. I wanted to know if a two inch diagonal was "worth it", given the pinch point coming out of the visual back. So I ran some comparisons with several eyepieces, with both a 1.25" diagonal, and with a borrowed 2" - both from Meade.
At 12.7m of distance from the front of the scope to a meter stick, the diameter of the visual field was:
In the 1.25" category:
24mm 68 degree Explore Scientific: 19.9cm ~ 0.9 degrees TFOV
40mm Orion Plossl: 20cm ~ 0.9 degrees TFOV
In the 2" category:
30mm Skyline Erfle 68degrees: 23.7cm ~ 1.07 degrees TFOV
30mm Explore Scientific 82 degree: 28cm ~ 1.26 degrees TFOV
Please forgive me if I'm calculating something wrong. I'm figuring these angles based on my eye being at the lens at the front of the telescope.
So you do get a significant increase in TFOV using the 2" back. There was some slight chromatic aberration at the edges of the ES 30mm, and the field wasn't super flat all the way across, but I think I've decided that the 2" diagonal would be worth it. While that 30mm ES is verging on being the same size as the OTA, for a scope with long focal length (my other scope is a 12" Dob), getting a wide angle view seems valuable. Haven't had the chance to do a comparison at night, but I know its worth a try now.