It is less a bother to post-flash, latensify, an entire roll of film
Originally Posted by fhovie
than to pre-flash an entire roll of film. May be that goes for
sheet film as well. Dan
Claire has said that it will ADD a bit to Fb+f. Add, I'd suppose, to
that which one would usually expect. I, like fhovie, don't see where
the results differ twixt the post long or the short pre exposure.
Pre-exposures are though more of a bother.
I do like the idea of a short, in leaky darkroom, post-exposure. I
reread a rec.photo.darkroom post. A #3 filter but no time
was suggested. Or I could, perhaps, just bring the film
out of the shadow a short while.
Then there's that fog, all over everything. I wonder if it's just a
matter of following instructions. Like with fixer film strength 1:4;
use it that way a while and you will come to believe that is the
only dilution that will work.
How about this! I'll do a quick test with paper. I'll expose then
post-flash and compare with pre-flash. Perhaps I'll be the first
ever to post-flash paper. Dan
The short pre- or post-exposures that I'm familiar with are at an intensity above that at which Low Intensity Reciprocity Failure (LIRF) occurs. The post-exposure latensification mentioned by Claire occurs well into the LIRF region - so far in that very little overall fogging occurs. The extremely low intensity light is capable of amplifying the image, much like Becquerel discovered all those years ago. Latent sub-image centres (Ag2, stable, undevelopable) can become latent image centres (Ag4, stable, developable). The light intensity is such that most non-image grains never become developable - they only ever get to be non-latent image centres (Ag1, unstable, undevelopable) that recombine in an instant.
I'm using 'Ag2' etc to mean two silver atoms together.
It is like the reverse of hypersensitisation - in which all grains become latent sub-image centres, so that it only requires one good photon to push the sub-image centre to an image centre.
Hope that makes sense.
Out of curiousity I did a quck check, and sodium perborate IS avalable as a granular solid. One source that lists it is a company I've bought from before The Chemistry Store http://www.thechemistrystore.com in FL. I'm going to try making some from the hydrogen peroxide formula, and if I find it's something I like will probably buy a 5lb pail from them, as I believe it was something like $8.00 or so for what would be a long time supply.
I'm curious, would changing the strength of the dilution from 1% to 2% or even 3% change the amount of speed increase in the film?
David Vestal wrote a good article about latensification in Darkroom and Creative Camera Techniques a few years back. His approach was to hank a whole roll some distance from green safelight such as is used for development by inspection for something like 15 minutes. I worked on a contraption to do that while you worked on other things. It was a wheel shaped thing about a yard across with a puller-inner worked by a crank. A green LED was to be at the center, reflecting off a very small polished hehisphere. This reflection is practically a point source. One would load it in the dark, cover the entrance, set a time, turn on the LED and have a cup of coffee or make some prints while it was cooking. Matbe I'll get around to finishing it someday.
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A little kid passed by and read over my shoulder, "Oh, I get it, it's just like skin, film that is. When you go to the beach to get a tan, you can go and get burned or you can ahead of time go to a tanning bed and get the tan started". (one of the problems of using the internet at the library)
Keep in mind
It needs to be done after the film is exposed. It is not the same a pre-exposure. It needs to have a minmum of 15 minutes and requires really dark conditions. It will only work with film that has been exposed to normal conditions...it will not work with film that required reciprocity compensation for exposure correction, I know of no reason that low light latensification can not be used on a frame that was pre-exposed but one would have to be quite careful not to get a very low contrast result. I did not get spurred into trying this idea from David Vestal but a from a Vestal edited article due to work and writing by Ralph Steiner and that David did a wonderful job of editing, Although I had read about it at least 30 years earlier I finally get around to trying very recently.
You need to do your own work to set it up. The light level being used is so dim that one can hardly see it much less measure it and specify a set up.
Originally Posted by Claire Senft
I was intrigued by this suggestion, since I'd not heard of it before, despite some 35 years in the film-developing game. Maybe I did, but it didn't register on the radar. Anyway, I tried it today. Took my Rollei SL-66 out with two backs, each loaded with Delta 400. I have previously established that for my developer, ISO 200 is normal. So I shot one roll at 200 and the other at 400 (to be treated with the perborate solution later). I metered for a Zone V exposure, (high, bright, even overcast) and then shot several bracketed exposures of each scene with each back.
I treated the roll shot at 400 in the perborate and then developed both rolls at my usual time in my usual soup (Phenidone, Vitamin C, metaborate). I then contacted and made prints from several of the scenes from both rolls. Strangely, I did not get the increase in film speed you suggest--at most about a third of a stop. In fact, in each case, the roll shot at my usual 200 and left untreated by the perborate was the better negative, giving me the fullest range of tonal values and shadow detail without blocking highlights.
Is it possible, do you think, that the T-grain structure of Delta film is not susceptible to this pre-development treatment? Perhaps I should try again using FP4+ or Fuji Neopan which are more conventional grain films?
I did not notice any increase in grain, as you said would be the case. It's a simple treatment, but only worth it if it really does increase film speed.
what can I say.
It is not a technique that I dreamed up myself. I got very close to 1 stop increase in film speed. And I got it with regularity. However, I got even more with low level light...asa 64 to 200 with 100TMax and an icrease in shadow contrast. Try a shadow based exposure and try again with two 1dentical placements on Zone 2 or three and see if it helps. I first picked up on this technique from an article written by a Mr. Pericano...I hope I spelled his name correctly. If my memory serves me correctly, One article was about monobath developers, another was about kallitypes and a third was about desenisitizers and there may have been a fourth. I believe that the monobath article mentioned it but I don't know which of the other 2-3 mentioned it. All of the articles appeared in the finest..my opinion..photography magazine extant. Photo Techniques. What else would one call a photo magazine that publishes those neat articles by Patrick Gainer? I should have been a bit more moderate in my statement and have said that it can add up to 1 stop of film speed.
I believe that if you use Google and type in "film latensification" or "sodium perborate" you can find other information useful to you about it.
I'll try your suggestions with meter placements on lower Zones. I did notice some improvement in shadow contrast in yesterday's experiments, but not a true increase in speed. The best printable negs from the perborate treated roll were those exposed at the same ISO--200 as the non-treated roll.
Originally Posted by Claire Senft
Although I've been a subscriber to Photo Techniques since its beginnings, I don't remember those particular articles, but since I've still got all the back issues, I'm sure I can find it. Of course, the fact that I can't remember something is no great issue these days. In my second half-century, my data bank is pretty full, and my apparatus for accessing long-buried data is becoming increasingly unreliable.