Originally posted by Thomas I put one on a 645N and very slight darkening of the corners at 28mm; gone by 29-30mm, but as pointed out above, viewfinder is less than 100%
Well, that's already better than I was expecting, if it ends up being usable by 30mm, that'd be the equivalent of 19mm in small format.
The word "usable" might have different meanings for a lens maker and photographer, even if it's simply not very sharp at the edges or has a lot of vignetting, I would still consider that usable in some cases.
Would be too much to ask of you to sacrifice a slide of film to see what the image looks like at 28mm?
Originally posted by lats Isn't the image circle of this lens published somewhere?
Nope, you'll find that very little is known about the IC coverage of just about evey lens that isn't intended for tech cameras.
If you were to buy a full-frame lens, it's pretty much expected that you'll use it on a camera that at most has a sensor of 36x24mm, even though the IC of lenses intended for this format can vary quite widely, with some having been tested to cover an area as large as 40x40mm.
Meanwhile, lenses with reduced image formats, such as those for APS-C variants of many DSLRs, are physically modified to not be able to fit on full-frame, so it's usually not known either as people don't want to modify their lenses just to find out.