What made these marks?

[GRHazelton]

I recently received some C-41 120 negatives and prints from a lab I've used in the past with satisfaction. While the prints are fine, the last two or three negatives display, on the base side, some regularly spaced marks. These marks didn't show on the lab's prints, but they are really evident on scans I made with my Epson V700. The film was Fuji 400 speed, I used a Pentax 645n, if that info makes any difference. Film cleaner won't remove them, an email to the lab hasn't been answered. Any ideas?

 

[cinejerk]

I don't know about that pentax but that pattern sure looks like the pattern on the pressure plate on my Mamiya M645. I really don't see how that could have happened though.

 

[brucemuir]

It almost looks like the pattern I've seen on some film backs pressure plates.

You did say it was 120 so I kind of doubt a waffle effect from the pressure plate.
Will be interesting to see what others think.

 

[Brian C. Miller]

Look at the surfaces of the film, front and back, and see if you can spot the pattern as dots on the film itself. It may have something to do with the processing machine.

 

[frobozz]

Turned out to be the processing machine in this case:

(there was a url link here which no longer exists)

Duncan