Quote Originally Posted by The Man from Mona View Post
They're both P67 lenses so there is a crop factor associated with using a "Full Frame" camera. It's not quite a 2x crop, maybe a 1.8x.
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There is NO crop factor when using medium format lenses on FF (35mm) cameras with adapters. A 105mm lens on a Pentax 67 is still a 105mm lens when attached to any other body, and it behaves like any other 105mm lens. I use Mamiya medium format glass on Canon FF bodies all the time so I'm not guessing or theorising about that either.

What you're referring to is the field or angle of view that the lens gives for any given format. A 105mm lens on 6x7 gives a field of view which is considered to be about 'normal/standard' and that lens that gives the same field of view as a 50mm lens on a 35mm body. However when you attach a 105mm lens on a 35mm body it will behave EXACTLY like a 105mm lens (clearly) and give you the field of view than any 105mm lens would (ie telephoto).