henry link
Well-known member
As was mentioned earlier in the thread it was Henry that first checked out the Zeiss HT 8x54 and found high levels of aberration. Others including myself didn't find if sharp either, and I passed on these observations to someone at Zeiss and invited him to have a look at the stopped down resolution. At a subsequent meeting he produced MTFs for 54mm and 20mm apertures, but refused to let me scrutinise them. I'm no expert in reading upside down down semi-log plots in apparent cycles per degree, but I made a note of my best guess at the x-axis values. For 54mm I made it 2.5 arcseconds (135/D) and for 20mm, 9.5 arcseconds (190/D). I would like to think I would be within 0.5 arcseconds of the actual value but I cant't be sure. Those values, or anything reasonably close, would definitely explain user complaints though.
David
Hi David,
Here's a link to my review of the 8x54 HT:
https://www.birdforum.net/showthread.php?t=285414
In post #16 my measurement of the full aperture resolution was 189/D and my estimate of the the resolution when stopped down to 22mm was 135-140/D. Those are in such good agreement with the Zeiss MTF, if its numbers are reversed, that I can't help but wonder whether it was mislabeled or misread. Can you think of a likely scenario in which the center 14% of the surface area of an objective lens would have higher wavefront error than the full lens?
Henry