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Mark,
I know this thread is now quite old but I thought I should add what I could to it based on my own experience with the 2" 30mm GSO Superview. I actually got the 1st of these into the country from Lee Andrews in late January 04, which is before they went on sale in the US.
Very nice review BTW.
The eyepiece was originally marketed as having a 68 deg AFOV and the 1st thing I did was to test this using the "drift timing method" as opposed to measuring the inside diameter of the barrel skirt which acts in place of the non existent field stop ring. Using the drift timing method I calculated the AFOV to be 65 deg. The manufacturer has subsequently amended their claims on AFOV to the same 65 deg, so I think this is something everyone can agree upon despite the fact there are still numerous dealers worldwide claiming AFOV's up to 70 deg.
In terms of optical performance I came to a very similar conclusion to you.
At F5 it works very well with the outer 10% to 15% of the FOV softening a TAD but still useable. At F6 and slower it does a very good job across 95% of the FOV and as you mention this poor 5% is quite likely due to the lack of a defined field stop.
Light transmission, sharpness and contrast are suprisingly good, not to the standard of Pentax or Televue but very good given the price level. I think it offers 80% of the performance of the 27mm Panoptic at 20% of the price, I would think close to easily the best value currently available in budget 2" widefield eyepieces. As you stated still good value if its price doubled. During one comparative test the eyepiece easily outperformed a somewhat more expensive UO 2" 25mm MK70 (modified Konig) in my own 10" F5 dob and the C8 we had on hand at the time, in all important areas including sharpness, contrast, light transmission and EOF, which was all the more impressive considering the 5mm difference in focal length.
I have subsequently tested the smaller 1.25" 15mm and 20mm GSO Superviews and can't rate them as highly as their 2" cousins. Whilst they still do a fair job considering their price level, relatively speaking they do not perform nearly as well as the 2" versions, particularly at F5.
CS-John Bambury
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