"MangroveRoot" wrote

If the lenses you use for your 645 are attached directly to the body, and
especially if your 645 has a built in TTL meter, the answer is "no." If
your lens attaches via a bellows, and your 645 doesn't have TTL, then the
answer is "yes." The greater the extension of the lens from the body, the
greater the required exposure.

That would be a "no" on both counts.
I *do* have a set of metal extension tubes, but that's not the same thing.
I was just curious. Sometimes it's nice to know more than I think I'll
need.

Oh yeah - extension tubes. I forgot about those things. ;-) Extension
tubes serve the same purpose as a bellows, so it IS effectively the same
thing: they/it push your lens further from the film plane than it would be
if mounted directly to the body. The greater the extension, the more you
have to compensate for light loss.