F-stop change with Kiev adapters?

[themoleman342]

I'm looking to adapt either pentacon or kiev 88 lenses to m42. The adapters essentially are like an extension tube because of the dramatic difference in register distance between the formats. Does anyone know what the f-stop adjustment would have to be? Or is it that the original aperture is non-applicable because of the difference in formats? I think I may just be over thinking things....Many thanks in advance!

[Attila]

[Farside]

When you use MedFor lenses on a smaller camera via an adapter, the lenses are still MF lenses and the film/sensor plane is where it's supposed to be, so no, you don't need to calculate a different f-stop. The adapter isn't functioning as an extension tube.