Sky 90 - Flattening

I have had my Sky 90 for a year. At first I was surprised at how out of focus the stars were off axis. I had inquired about it, I think the dealer said, that's normal, but wasn't sure it was correctable with a flattner / reducer, for visual... or something like that. I also have a FS128, which, of course does not suffer the same issue. Anyone out there have a flattener reducer, does this fix the problem and allow for edge to edge sharpness? Any other side effects. Any input welcome. I think I would really appreciate viewing with edge to edge clarity. Thanks, George

I have mostly Naglers 31, 22, 16, 12... etc to 2.5. and a couple of Televue 62 degree ones... forgot which line. So your saying Panoptic's wouldn't do this?

G

George Prentice said:

I have had my Sky 90 for a year. At first I was surprised at how out of focus the stars were off axis. I had inquired about it, I think the dealer said, that's normal, but wasn't sure it was correctable with a flattner / reducer, for visual... or something like that. I also have a FS128, which, of course does not suffer the same issue. Anyone out there have a flattener reducer, does this fix the problem and allow for edge to edge sharpness? Any other side effects. Any input welcome. I think I would really appreciate viewing with edge to edge clarity. Thanks, George

At f5.6 with a doublet, even with a doublet with one fluorite element, edge performance due to spherical aberration is pronounced. I have never tried mine with the dedicated flattener/reducer so I don't know if it would be better or worse. I do know that the extender-Q does help significantly but it is essentially a 1.6x barlow and as such takes it up to around f/9. So much for the wide field views.

Maybe look into replacing it with a TMB92SS?