DanC.Licks
AKA Daniel Bradley
Vignetting is not usually a problem with APS-C sensors, but only with full frame if the scope has only a 2" focuser. FF requires a 3" focuser. The 4/3 format is nice for scopes for two reasons, more reach and a closer to square format. I have both 4/3 (Oly E-30....maybe E-M1 sometime) and APS-C (Nikon d7000, maybe D7100 sometime) and although I normally prefer the 3/2 format for normal photography, I find 4/3 better for birds, which is about all I do with the scope anyway. Keep in mind that an APS-C sensor cropped to 4/3 format is only slightly larger than the 4/3 standard size. Enough bigger to give it a slight advantage in DR and noise, but not really a huge amount. There was quite a difference between the E-M5 and the D7000, but the difference between the E-M1 and the improver sensor in the D7100 seem to be more evenly matched. Still no figures from DxOMark to base this on, but the test shots I have seen indicate a big improvement in 4/3 sensor technology.