By "field of view" do you mean the angle of coverage -- basically the angle of the Image circle -- or the picture angle -- basically what the film sees?
The angle of coverage is format independent -- it's the same regardless of what film size you are using -- and can only be used relative to the diagonal / diameter of the IC.
The picture angle is format dependent -- and can be used relative to the horizontal, vertical or diagonal dimensions of the film format being used (which, of course, can vary slightly based on the film holders being used).
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