Question about 70mm backs

So I ended up listening to the dumb voices in my head again and bought a Pentax 645 with three backs. Among these is a 70mm back (I blame my crazy voices on that), and it got me to wondering if the 65mm films were compatible. My research would suggest that it was, but I can't find any one talking about it

So, has anyone tried using 65mm film in their 70mm equipment, and what was your experience?

No, they are not. The designations are their nominal width, and the 65mm film, for taking, is 5mm more narrow, as it does not need to take soundtracks at the rebates as the 70mm projection one.

Thus the perforation-row spacings at the still- and the cine-70mm versions are different.


You thus need the still version !

Good luck finding such.

AgX said:

Good luck finding such.

Click to expand...

B&H has 70mm HP5 in stock. Unfortunately, I don't know of any commercial lab which still develops either it or the C41 I have in my freezer.

If I had a commercial lab with a dip&dunk processor I would find a way to make a stable festoon and to please my customer.

Having received the camera and the backs today I see the possible issues if I tried to use 65mm in this back. The sprockets are used for frame counting from what I can see, and the roller is slick compared to the rollers for the 120 and 220 backs. If there was a service to convert this to use unperforated film with a higher friction roller for frame counting I would see no issues using 65mm film in this back.

Would it be possible to apply some friction enhancing substance to this roller?.

I know my other option would be to trim 65mm down and make 220 rolls.