Helinophoto
Member
Also, how does IR film differ from non-IR films; does it solve any of these concerns? Is my thinking just nonsense?
My experience with close-up IR is mostly with *D* and long lenses (birds) and the difference is small, IR cause maybe 1 inch backfocus when you are within 2-3 meters from the subject with a 400mm.
Further away with my 400mm f5.6, I got consistent and noticeable backfocus on birds, up to 20 cm when they at 5-15 meters ( at f7.1-f8)
I've also done model-photography in IR, but on those, focus seemed to be just fine with my 70-200 f2.8 (at f4).
With landscape, I've never really experiences any issues (*D* and medium-format up to 6*7)
But to compensate, you need to pull the focus-plane towards the camera a little, the red markers on the lenses may be a good aid (best suited for still subjects).