I was (I think) the person who originally posted that SK BR lenses can be used on Alpa tech cameras through a simple Alpa-Mamiya adapter, available from Alpa. That small discovery helped fill a niche for me—large-aperture lenses on a tech camera, enabling, for example, an extremely compact 80/2.8 Alpa TC12 with handle and IQ4 that just fits (with two spare batteries!) in an F-stop Micro-Tiny ICU. I attach this ICU to a shoulder strap, resulting in a discrete 80 mm f/2.8 53x40 mm 150 MP camera and lens that is carried—with reasonable padding— in a 4"x6"x8" carrier that is smaller than most small ladies' purses and can be taken just about anywhere. For landscape shooting the 80/2.8 SK BR lens gets replaced with a 50/4 Rodi HR or a 32/4 Rodi HR, both of which also fit in the same F-stop Micro-Tiny ICU with TC12 and IQ4 and all necessary spacers.
However, for my own uses I don't see much benefit adapting the SK BR lenses to a Sony a7 or a9 body—the loss of autofocus and aperture variability compared to the already excellent and very compact and (by MF standards) reasonably priced Sony FE lenses is a lot of loss for little gain, for me at least. I appreciate that there will be niche uses, plus potential cost savings, of such an adaptation, however.
I would love for some to release a mirrorless AF body (much more compact than the XF) that can use the IQ4 back, but until that day arrives, I've been using a combination of live view and mounting a Leica Disto on my Alpas to focus. And when I have to get the shot and the subject or conditions are challenging, I break out the Sony a7r3.
However, for my own uses I don't see much benefit adapting the SK BR lenses to a Sony a7 or a9 body—the loss of autofocus and aperture variability compared to the already excellent and very compact and (by MF standards) reasonably priced Sony FE lenses is a lot of loss for little gain, for me at least. I appreciate that there will be niche uses, plus potential cost savings, of such an adaptation, however.
I would love for some to release a mirrorless AF body (much more compact than the XF) that can use the IQ4 back, but until that day arrives, I've been using a combination of live view and mounting a Leica Disto on my Alpas to focus. And when I have to get the shot and the subject or conditions are challenging, I break out the Sony a7r3.