Hi, is there a known Yashica to Rollei QBM adapter? When googling for that, I find many topics where people want to use a QBM lens on other systems, but in my case I wonder about the possibility of using a lens with Yashica mount on my Rollei 3003..
Unfortunately not.
Assuming you're talking about the Contax/Yashica mount (and not M42 screw or Pentamatic) this has a flange focal distance (FFD or register) of 45.5mm, while the Rollei/Voigtlander QBM mount is 44.6mm. This leaves less than 1mm for an adapter if you want focusing to infinity. Such thin adapters are sometimes possible, but only where the lens bayonet is much smaller in diameter than the body one, which isn't the case here.
https://www.graphics.cornell.edu/~westin/misc/mounts-by-register.html
It may be possible to replace the mount on the lens and retain infinity focus. You'd need a donor mount from another suitable lens, plus some DIY skills and tools or cash for an expert conversion. 3D printing a replacement mount is also a possibility. You'd lose automatic diaphragm and full aperture metering, but stopped down metering would work in manual and aperture priority auto modes. Here's a commercial example of how Zeiss C/Y lenses can be modified to fit onto Nikon cameras:
http://leitax.com/Zeiss-Contax-lens-for-Nikon-cameras.html
Depending on the resale, collectable and/or sentimental value of the lens this may not be worthwhile... it would usually be simpler and often cheaper to sell your lens and buy one in Rollei fitting.
Hope this helps.
ps. I just noticed you said "lens with Yashica mount" and not "Yashica lens". If you have an independent lens in Yashica/Contax fitting it might have an interchangeable mount (Tamron Adaptall for example). If you confirm exactly what the lens is I may be able to provide more specific advice.
