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The film in the BTZS video has been developed and stopped, if it's the one I've seen before, and then being moved to the fixer, not being put back into the developer. I think it's a bad idea either way, but if you're planning to develop part of the roll longer after exposing it to light, then it's a REALLY bad idea.
IR goggles are probably the safest method, or traditional development by inspection with a green light, as long as it's not T-Max, as Greg advises.
But even if you can see what you're doing, handling a roll of wet film and respooling it wet without scratching it isn't easy.
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This is an interesting question; I for one am glad you asked!
In ye olden days, people used to use certains dyes as desensitizers, like pinacryptol yellow. It had the same effect as sensitizing dyes, only the opposite effect. This allowed development by inspection, even with panchromatic films I believe.
And could someone explain the whole green safelight thing. Why green? How does that not fog the bejesus out of any film??
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 Originally Posted by michaelbsc
If it is 35mm then note the frame (Write it down! Don't plan to remember it), rewind, load the other ISO film, and when you reload the first film shoot 2 frames past the point with the lens cap on.
It occurs to me that *if* one had a roll where this had already happened---maybe you bumped the ISO dial in mid-roll without noticing, or whatever---you could use this approach to cut the roll in two *before* developing, if you know roughly when the problem happened.
Rewind the film, reload the film, shoot and advance with the lens cap on until you reach the "cut point" frame, then take the camera into the dark, open it up, and cut at the edge of the film gate (by feel). Voila: you have two segments of film, which can be loaded and processed separately. Hopefully you got the right frame number and each half is exposed consistently; even if you missed by a little, you only messed up a few frames instead of one whole half of the roll.
But I agree that the best solution is to avoid making the mistake in the first place. That approach works well for those of us who only make the mistakes we planned to make. :-)
-NT
Nathan Tenny
San Diego, CA, USA
Although the moon is smaller than the earth, they are about the same distance apart.
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Originally Posted by holmburgers
This is an interesting question; I for one am glad you asked!
In ye olden days, people used to use certains dyes as desensitizers, like pinacryptol yellow. It had the same effect as sensitizing dyes, only the opposite effect. This allowed development by inspection, even with panchromatic films I believe.
And could someone explain the whole green safelight thing. Why green? How does that not fog the bejesus out of any film??
Green is where YOUR eyes are most sensitive so you can expose it the least.
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If I have understood the OP correctly he knows from which frame he had to change the speed. He would then be able to retrieve the film in the total darkness and having marked out on a bench the length of film he needs to cut with say two pieces of masking tape he cuts at that length, develops first length while storing second length then develops second length.
If it is 35mm then unless he is very lucky or extremely accurate he will ruin or part ruin two frames but better than than under/overdeveloping a whole section which was exposed at a different speed.
In the future and if forced to change speed then as others have said he can fire two blanks which should give him sufficient safety margin to cut the film in the dark at the blanks and develop separately.
pentaxuser
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What was the Exacta model with the built in cutting blade?
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What was the Exacta model with the built in cutting blade?
My VX IIb has it
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i have dbi with a green filter
tmx/tmy for 10 years without any bad effects
i dbi so tmz last night ... no problem
( luck i guess )
if you can experiment a little
and try this with a roll that means nothing rather than one that means
something ...
get a dark green filter,
after you do your primary development,
wash your film
pull it off the reel to the frame you want to cut ( shoot a few blanks so they are easy to spot )
and turn the green light off again.
reel the loose film onto a second reel and fix it ...
you might get good, where you know a 36 exp roll is 6feet long, you judge 3 feet,
flip the green light for 4 seconds, cut the film ... and reel it
good luck !
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Originally Posted by bdial
What was the Exacta model with the built in cutting blade?
My VX IIb has it
Do you ever use the feature with the old style canisters that close when you turn the bottom lock?
Or do I misunderstand how it works?
I have never seen one other than as a web picture.
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Thanks to all for your input. I'm glad the thread went a little off topic, because my initial inquiry was a silly one. In the end I stuck to a uniform ISO for the whole roll.
I am familiar with the trick of rewinding and swapping films and reloading using a 2 frame buffer. Done it before with success. Thanks again.
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