In the post just above yours I mentioned that the Apo-Grandagon 55/4.5 produced a lot of lens cast on shifting on my GFX 50R. Perhaps I am a source of "Some reports"? That's not the only issue though. I'm not using an Actus so I can't say for sure whether or not the rear of the lens clashes with the camera standard on an Actus, but it does on my VX23D outfit. This is a function of the flange distance of the lens and the depth of the sensor inside the GFX camera.
I have a long-shot option for you to think about. I just started using a modified Mamiya G 50mm f/4. It's meant for the 6x6 Mamiya 6 camera, so the image circle is large but not enormous like the Apo-Grandagon 55/4 or its cousin the Apo-Sironar Digital 55/4. Nonetheless, it is large enough to allow for 15mm of shift. Best of all, even though it's a symmetrical lens designed for a rangefinder, there's no lens cast that I can see even at 15mm.
The performance of the Mamiya G 50/4 is outstanding. It reaches what I would call peak performance at f/8. Wide-open at f/4, it's excellent in the centre, but the edges and corners are a bit softer. Colour is a bit on the warm side, but easily corrected. There's no CA that I can detect. Close performance is as good as long distance performance. Distortion is minimal, even shifted to 15mm. It's superb. I also use the Mamiya G 150/4.5, and it's even better -- outstanding from wide-open.
I also have a Fuji GF 50/3.5 so I have made head-to-head comparisons. In summary,
- At long distances, the GF lens resolves a bit more detail than the Mamiya G, but not a lot, and you have to magnify considerably to see the difference. To my eye, it's not photographically significant in most cases.
- At long distances, the GF lens is extremely good across the field from wide-open. It's a very consistent performer -- really superb value. In contrast, the Mamiya needs f/8 to be superb across the whole frame on my setup. I emphasize "on my setup" because slightly degraded performance below f/8 at edges and corners may be caused by parallelism problems on my camera. I need to evaluate this further to be sure.
- Where the GF 50/3.5 falls down is close distances. At or near the minimum focus distance edges and corners are soft, and never become critically sharp. Minimum focus distance on flat targets is hardly the use case for the GF 50/3.5, so I accept the compromise the Fuji engineers made. However, by f/8 the Mamiya G is critically sharp across the whole frame on the test chart, and it's better wide-open in the corners than the GF is at f/8.
- CA can be very bad on the GF lens, even at f/8. It varies by scene and focus distance. In the same scene, with a minor change in focus, I've gone from acceptable to useless. In that same scene, the Mamiya G lens has been consistently free of CA.
- I find the GF lenses to be rather cool and bluish. If you only shoot GF lenses you might not notice, but put beside my older Schneider, Mamiya and Pentax lenses, I notice. I prefer the colours of the older glass. This is of course correctable, but it's something to keep in mind if you shoot GF lenses alongside other lenses and need colour consistency.
- Finally, the GF 50/3.5 is a bit wider than the Mamiya G 50/4. If the GF lens really is 50mm, then the Mamiya G is around 52mm. I wish it had been the other way around, but so it goes.
Here are the two lens in a side-by-side at 100%. This building is 600m from my position, and both lenses are focused at a target approximately 4km in the distance. Lightroom's default sharpening is used (meaning it's a bit heavy-handed, especially for the GF lens). I adjusted the colour temperature of the Mamiya (cooler), and exposure of the Fuji (lowered). I should emphasize that the Mamiya is wide-open at f/4, while the Fuji has been closed down 1/2 stop to f/4. A clue that the Fuji is resolving a bit more is the aliasing under the sign for "the co-operators". It's present on the Fuji GF image, but not the Mamiya G image.
View attachment 181582
Adapting a Mamiya G lens require permanent modifications that will make it unusable on a Mamiya 6 camera -- so forget any notion of using G lenses on both. If you want to do that, without shifting, Fotodiox makes an adapter for Mamiya 7 lenses on GFX cameras. To use a Mamiya G lens, you have to lock the shutter open. And to mount it conveniently, you have to replace the Mamiya 6 mount with something else because there are no adapters for any camera. The work is not very expensive. Locking the shutter open is not something I could do myself; I had an excellent Mamiya technician do that for me (Bill Rogers in Las Vegas). I'm building my own mount solution.
Full-size JPEGs for wide-open to f/22 for both lenses are available from a Google Drive folder I've shared via this page (scroll down to the bottom):
https://www.robdeloephotography.com/Pages/Toyo-VX23D-and-Fuji-GFX-50R My only caveat about those files is, as noted aboe, some of the softness at wide apertures on the Mamiya G 50/4 that I'm seeing on the right-hand side of the frame may be due to parallelism problems. I'm using a temporary mount while I'm waiting for the bits and pieces I need to build my replacement mount to come in; the temporary mount might be ever so slightly off -- enough to be noticeable at f/4 and f/5.6.
