[LargeFormat] Macro depth of field

[Mike Finley]

I shouldn't have tried to put extra questions in my introduction, as they
weren't expressed very clearly!

When asking about depth of field in 5x4 and roll film formats I had in mind
the following:

Say I want to print an image 3 times life size (final image size 10"x8").

If I use 5x4 I'm enlarging the negative 2x, so need to shoot at 1.5x life
If I use roll film I'm enlarging the negative 4x, so need to shoot at 0.75x
life

There are then two things affecting depth of field (assuming same lens and
aperture):
I can use a larger circle of confusion on the 5x4 negative, as it won't be
enlarged as much, increasing depth of field.
I am shooting at a higher magnification on the 5x4 (1.5x rather than 0.75x),
decreasing depth of field.

I think, from looking at a couple of negatives, that the latter has greater
effect, giving me overall less depth of field with 5x4 film than a roll-film
back, assuming the same aperture. I haven't tested this properly though.

Can anyone confirm this?

thanks,
mike