Re-exposure after bleaching bw cine film?

[Praktica_enjoyer]

Hi everyone,

I had a quick question: do I need to unspool the film from the reel when re-exposing it after bleaching, when working with bw reversal film?

I finally caved in and bought a LOMO UPB-1A and I have this double 8 reversal film I've been meaning to process for a while but I'm not quite sure of what to do. Having to unspool the wet film and having to respool it for the second developer sounds nightmarish, and also like a huge risk when it comes to fingerprint marks.
The reels are transparent, so light can obviously pass through, but I'm scared it that the exposure would be pretty uneven if I simply hit it from the top... Is there such a thing as overexposing a bleached film? Does it just stop mattering after a given amount of time and it just evens out? Everywhere I look says to do 1-2min, would any more be detrimental to the film, or is 2 minutes already more than enough?

I do still have a 35mm roll of the same filmstock (foma r100) from when I tested the homebrew recipe I found on a person's website, so I could develop that roll in the LOMO (would be a bit silly, but I really don't wanna mess up that roll), in case no one is positive (pun intended) about what to do exactly.

 

[koraks]

AFAIK most people do the re-exposure with the film on the reel.
It's generally very difficult to get wet film back into a reel, esp. the plastic reels.

 

[dokko]

I developed hundreds of films in the lomo spirals, never took them out for re-exposure and would strongly advise against doing so. It’s slow and cumbersome and the risk of damage is quite high.

Never had and problems with exposing in the spiral, it‘s transparent and allows light to come from all sides, so just move the spiral so it allows exposure from all directions.
Kodak mentiones 800 footcandle seconds of exposure for Tri-X reversal (ie 200 ISO), so your Foma R100 should be around twice that.

I use a 60W LED film light, at 1meter this means only a couple of seconds exposure is needed. i usually do around 30 seconds while moving the spiral in all directions just to be absolutely safe.

 

[Praktica_enjoyer]

Ok, great! Thank you so much for your input!

 

[Raghu Kuvempunagar]

Kodak mentiones 800 footcandle seconds of exposure for Tri-X reversal (ie 200 ISO), so your Foma R100 should be around twice that.

I am not sure one can arrive at the second exposure time based on the film's ISO. After bleaching, the sensitivity of the film won't be anywhere close to its original sensitivity.
That's why the recommended exposure time is a few minutes and not a fraction of a second. The bleach used in reversal processing is a strong oxidiser and it desentises the residual silver halide in the film. It also renders waste the senistising dyes used in the emulsion. So what we have for the second exposure is a blue-only sensitive very slow speed emulsion. Fortunately, second expsoure need not be very precise and one can err on the side of reasonable over exposure without negative consequences.

 

[blee1996]

I use a 60W LED film light, at 1meter this means only a couple of seconds exposure is needed. i usually do around 30 seconds while moving the spiral in all directions just to be absolutely safe.

A question for clarification: 60w actually power rating for the LED light, or LED light with equivalent brightness of a 60w incandescent light?

 

[AZD]

I would suggest “equivalent”. Tungsten is something like 10% light and 90% heat per watt. LED is far more efficient, so actual 60W LED is crazy bright.

 

[dokko]

I am not sure one can arrive at the second exposure time based on the film's ISO. After bleaching, the sensitivity of the film won't be anywhere close to its original sensitivity.

Would be interesting to know how much the sensitivity drops.
I would expect it‘s similar across different brands of film, so if Kodak says 800 footcandle seconds for Tri-X it seems reasonable that Foma R100 is about twice of that.

I just did some calculation and it seems that unexposed 200 iso film only needs about 0.2 footcandle seconds to get full density, so the reversal exposure is already 4000 times of that.
Kodak also mentions that 100x less exposure (ie 8fcs) still would result in underexposure of the reversal steps, so that gives a rough estimate.

A question for clarification: 60w actually power rating for the LED light, or LED light with equivalent brightness of a 60w incandescent light?

That is a rough calculation for a 60 Watt film light with reflector at 1meter (yes, quite bright, thus the short time needed).

A bare 60W tungsten bulb at 1meter distance (or 10W bare LED bulb) would more be in the order of around 2 minutes.

my favorite way is to expose it while submerged in a white bucket filled with water - the white bucket will reflect the light from all side and being submerged make sure there are no water dropplets acting as microlenses.

The whole thing is not very crritical, but it‘s worth pointing out that Ilford and Kodak mention there are possible downsides (fogged highlights) to massive overexposure (like more than 5-10x the recommended amount) so I would not hold it up to the sun

 

[Praktica_enjoyer]

my favorite way is to expose it while submerged in a white bucket filled with water - the white bucket will reflect the light from all side and being submerged make sure there are no water dropplets acting as microlenses.

That's actually really smart haha!

The whole thing is not very crritical, but it‘s worth pointing out that Ilford and Kodak mention there are possible downsides (fogged highlights) to massive overexposure (like more than 5-10x the recommended amount) so I would not hold it up to the sun

Ok, that's very good to know!

So from what I've gathered I'm better off using a less powerful light source for longer.

I actually looked up the films datasheet and it says:
"re-exposure is to be done in the developing tank using a 100 W bulb at a distance of 1 m in water and with the film moving (turning
the spiral with the film) – 30 sec from both sides"
So I'll probably do like 1.5x that, just to be safe!