I've been thinking about that as well. I dont shoot anything faster than iso 125 film in my toys, may be a contributing factor for not imprinting a number on my negatives. My Duaflex specifies 100 or 125 speed film, since the shutter/aperture is optimized for those, thats what I use. I've loaded a roll of Adox CHS 25 Art in the Duaflex this morning, cant wait to see what that gives me.
I have a Brownie Hawkeye, I can use a 120 roll in the feed, I need a 620 spool for takeup. If you have to send your film into a lab, be sure to ask that they return your spool.I have shot TMax 400 in my Brownie without problem in the red porthole.
Strange - I have used cameras where the red filter has fallen out of the hole in the back - leaving the backing paper exposed - and still not got an imprint in the film. I mostly use FP4+ and HP5+.
I'm not saying it's a good idea, just that I seemed to have got away with it.
Never tried it with Tri-X. Maybe some film backing papers are less lightproof than others?
My 6x17 camera has a plain clear window and I have no problems with even 400 ISO films. I have on occasions forgotten to close the window and even in the extreme sunlight in Turkey haven't had an issue with light passing through the backing paper with Tmax 400, Delta 400 & HP5.
I went back and dug out the roll I shot
with the Argus -- it turns out not to have
been Tri-X, but a film without markings.
I am guessing Efke 100 but I am attaching
a rough scan of a frame with the number
burnt in through window and paper backing
-- perhaps someone can identify the film
from the design of the frame number.