using polaroid back

I am trying to use a 545 polaroid back on my calumet/cambo 4x5 camera and
the question I have is how does one keep the focus that was in focus on the
ground glass the same as the final print. I seem to loose focus slightly on
the print. What is the secret to keeping the film in plane when using a
polaroid back?

Don

"Don" wrote...
I am trying to use a 545 polaroid back on my calumet/cambo 4x5 camera and
the question I have is how does one keep the focus that was in focus on
the
ground glass the same as the final print. I seem to loose focus slightly
on
the print. What is the secret to keeping the film in plane when using a
polaroid back?

First of all, make sure you place it all the way in, so that the ridge
finds the groove. Second, you might want to check the back for warpage.
As a last resort, try closing the aperture more.

To make sure it's the same distance from the lens as the ground glass,
take the lens off and measure the distance to the GG and then to the
back (with a sheet of paper and the slide in the open position) from
the lens mount. They have to be the same, naturally. If they are not,
you need to clean or fix the back...

Good luck!