T3D Focal length

[Tom Deering <tmd@xxxxxxxxxxx>]

I am waiting for the delivery of some bellows, which I will use to take
some macro stereo photos.

I'd like to continue to use John's formula, but I want to make sure I
understand the concept of focal length.  If I place a 45mm lens on a 100mm
bellows, do I now have a 145mm lens?   Is there a different way to
calculate focal length?  So far, I've done okay estimating, taking the
printed focal length, and subtracting the estimated amount that I've racked
it in to focus.

And does the formula work at such distances, or does it break down for some
reason?  I haven't received the bellows yet, so I can't run tests of my
own.  Yet!

Tom



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