Originally posted by whwang Don't have GFX 100, but have GFX 50R, and 645z, two cameras with identical sensor. After testing a few P645 lenses on 645z and GF lenses on the 50R at large apertures, I would say that I am totally not surprised by what you found. I can't be excited by a 100MP crop sensor from Pentax, unless Pentax also drastically revamp its lenses for 645.
Edit: went back and tried again to understand what was being shown.
I agree with Mazwick's assessment, but I do not expect lenses used wide open to be sharp for a viewer who is close to what is an extract of an image 15 feet wide (assuming it's being shown at 100% on a typical monitor). I never use lenses wide open, unless I'm particularly interested in razor-thin depth of field, which I'm usually not. For prints in the 10-foot range intended to display a sense of unending detail when viewed up close, I would find the 645 format to be a difficult challenge, requiring that I spend many thousands for
each lens. Traditionally, photographers brought their 8x10 cameras for such images--not even 4x5 would do. And those lenses are specified to be use at no wider than f/16 or f/22. At that degree of enlargement (70x), a lens would have to be used wide open to avoid diffraction being the main limitation.
I can't imagine a 10-foot print made at a wide-open aperture that provides only a few millimeters of depth of field--it would be extraordinarily difficult to get a sense of what the print is a picture of when viewed closely.
For me, 70x of enlargement demands compromises--either stop it down so that the lens works (at least as much a diffraction will allow it to), or make the viewer pace back and forth to find the part of the image that is actually in focus to even get a sense of it. If the viewing distance is far enough to avoid that, then looking at it at 100% on a display is unrealistic.
That 150 was never the sharpest lens in the line, being primarily a portrait lens, and used for making prints in the 16x20" size class for commercial portraits. I've had pretty few portrait clients that would tolerate more sharpness than that lens displays even at a wider aperture. I know that Mazwick considered other lenses, but that means I don't want to draw sweeping conclusions about these particular examples, and I certainly want to consider the use case being described here, and whether it is realistic. If I made prints that big, I'd get a full-frame back for a high-dollar digital-ready view camera, but even that would be challenged for prints that big viewed up close.
For a more reasonable 20x of enlargement, which is already
a lot, prints will be 25x35--two feet by three feet--and these lenses will not require nearly the same compromises to produce high quality results. But I still would find very few subjects that would be served by f/2.8 on a 150mm lens. Most of these lenses were designed for enlargements up to that point, and that's already beyond what most people actually do with these cameras beyond showing off 100% crops to each other on forums (concerning which I'm as guilty as anyone).
Rick "whose scans of 4x5 negatives look fabulous at 4x enlargements, but who would want to use an 8x10 camera with laser-scanned film for a 10-foot print viewed up close" Denney