Preflashing Ilford Direct Positive Paper

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TheSleepingPhotographer

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Does anyone at this forum have any experience with pre-flashing Ilford Direct Positive Paper before use in a large format camera? I am looking for information about this technique to do this with my photography students.
 
Yes, I do this constantly. Think I posted about it already ( or maybe that was Facebook).
What do you want to know? Joe Cleave covers this thoroughly on YouTube. He uses an enlarger and gives instructions for deciding on pre-flash exposure. His protocol would be useful for students wanting to understand the system.
I pre-flash in camera immediately before each exposure, using something a bit like a filter; 2 layers of highly diffused, transculent plastic. Believe the original material was the cover of a ring file. Other people use a couple of paper tissues and an elastic band, which would transmit roughly the same light. (Someone posted that they use the same tissues over a light meter to decide the exposure, and I still have not understood how that would work).
Does that help?
 
AnalogueWendy said:
Yes, I do this constantly. Think I posted about it already ( or maybe that was Facebook).
What do you want to know? Joe Cleave covers this thoroughly on YouTube. He uses an enlarger and gives instructions for deciding on pre-flash exposure. His protocol would be useful for students wanting to understand the system.
I pre-flash in camera immediately before each exposure, using something a bit like a filter; 2 layers of highly diffused, transculent plastic. Believe the original material was the cover of a ring file. Other people use a couple of paper tissues and an elastic band, which would transmit roughly the same light. (Someone posted that they use the same tissues over a light meter to decide the exposure, and I still have not understood how that would work).
Does that help?
Click to expand...

Thank you so much for the prompt and informative response to my query. It seems more elegant and simple to pre-flash the paper in-camera. I will do some experimentation with materials to see which diffuses most suitably for the process.
 
Presumably the meter with the tissues gives an integrated Zone Five reading. If you used it directly, this would give a Zone Five neg. For flashing, you need an exposure on the threshold, which would be Zone One. The flashing exposure would be 5 > 4 > 3 > 2 > 1 lower.
After that, you’d remove both lots of tissue and re-meter the scene for the image-forming exposure.
Flashing can be a bit of a hit-and-miss process, so experiment is needed. You might need to flash to a higher (or even lower) Zone to get the effect you need. If this is to demonstrate to students, then testing seems essential.
The tissue method sounds a bit idiosyncratic. The plastic sheet sounds better and there are lens caps made of something like polythene that might be more convenient.
I’m afraid I have no experience of direct positive paper in camera, so there may be better advice elsewhere.
 
I use the very unscientific method of a folded A4 sheet of white laser printing paper and stop the lens down 3 stops from my meter reading. It reduces the contrast of the paper sufficiently for my taste. The hardest part is knowing which exposure to use because we can’t meter for UV light.
I think I read on Andrew Sandersons excellent blog that the pre-flash only lasts around 4 hours so it’s not possible to pre-flash a bunch of sheets under an enlarger in the morning and go out for the day, hence why I do it in-camera at time of exposure.
 
That makes sense tactically too. Flashing is to adjust for the scene in front of you at the time. If you need to do it every time, you’re simply underexposing every time.
 
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