Curiosity had me dremel out the innards of a polaroid 545i back for the rb67 pro sd. This is just to report that the resulting frame size is a slightly irregular ~3" tall by ~2.75-3" wide. Or if you prefer, ~75mm tall by ~70-75mm wide. This was verified with 4x5" polaroid sheet film using various lenses at different focus distances.
The irregular width that I am reporting is due to two kinds of light obstructions in the actual body of the RB. There are minor notch-like shadows at each corner, but a larger irregularity in the width is due to the mirror detent in the body, which produces a shadow at the film plane toward the top of the loaded film. This irregularity appears unavoidable unless one does a bit of surgery on the mirror detent itself (probably not worth the bother, but of course I may well try it and report later if there is interest).
I have been shooting quickoads without incident in the 545i back for some time; I see nothing adverse to report. The RB lenses can all cover the picture widths amply. I see no issues with film flatness; the quickload sheets appear sufficiently stiff not to require a pressure plate or such, although diligent people might cut themselves a foam boundary to make themselves feel better about this issue.
I did see some corner shadowing with the RB 37mm fisheye, but this is actually from the built-in shade!
So, in summary, you gain about a ~1cm in both directions by doing this, not a huge amount but it does give some extra crop latitude and lets you get a bit more film exposed per pound of gear
The extra crop latitude may be especially useful if you plan to do perspective correction.
P.S. In principle, a similar thing is possible with the rz, but the 545i back for that has a quite different mount which encroaches more on the film and is a bit more difficult to work on.
The irregular width that I am reporting is due to two kinds of light obstructions in the actual body of the RB. There are minor notch-like shadows at each corner, but a larger irregularity in the width is due to the mirror detent in the body, which produces a shadow at the film plane toward the top of the loaded film. This irregularity appears unavoidable unless one does a bit of surgery on the mirror detent itself (probably not worth the bother, but of course I may well try it and report later if there is interest).
I have been shooting quickoads without incident in the 545i back for some time; I see nothing adverse to report. The RB lenses can all cover the picture widths amply. I see no issues with film flatness; the quickload sheets appear sufficiently stiff not to require a pressure plate or such, although diligent people might cut themselves a foam boundary to make themselves feel better about this issue.
I did see some corner shadowing with the RB 37mm fisheye, but this is actually from the built-in shade!
So, in summary, you gain about a ~1cm in both directions by doing this, not a huge amount but it does give some extra crop latitude and lets you get a bit more film exposed per pound of gear
The extra crop latitude may be especially useful if you plan to do perspective correction.P.S. In principle, a similar thing is possible with the rz, but the 545i back for that has a quite different mount which encroaches more on the film and is a bit more difficult to work on.
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