latensification

Discussion in 'B&W: Film, Paper, Chemistry' started by Claire Senft, Jan 13, 2005.

  1. Claire Senft

    Claire Senft Member

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    I have recently been experimenting with latensification by use of low level light. It is neat...really neat. For those of you who are unfamillar with this technique I will explain what it is. Latensification in this context is not pre-exposure involving shadow support by adding density from exposure to reflected light from a gray card etc placed on say zones 0 thru 2. Latensification with low level is usable with film that has been exposed to light within the normal limits that does not require reciprocity correction. For most black and white film this would be from say 1/2 second thru 1/2000th of a second. Some films will preform outside of these limits without reciprocity compensation being required. Latensification with light can only be done of the film has been already exposed. So the negative is exposed normally with the camera. It has to be exposed to low level light for a minimum of 15 minutes. The purpose of doing this is make developable a silver crystal that has not received sufficient photons to become developable. What this does is to increase shadow film speed by 1 or more stops. It will also add a bit to film base fog. When used in this manner it has the effect one desires when using a compensating developer to increase shadow detail. However useful compensating development is it also tends to reduce shadow contrast. Low light latensification increase both shadow detail and shadow contrast and should work with any B&W film and developer. As an example, I mainly use 100Tmax. When used with Pyrocat HD I used a film speed of 64 before I started latensifying the film. Now I get full shadow detail at a film speed of 200. There is no gain in grain size. I have increased my development time by 5% to restore contrast...when you lift the bottom it is closer to the top.

    What is required is tests to determine where to put the light and its brightness so that you get the maximum gain in shadow speed with minimum of fog as well as even coverage of the film. I have the light 12 feet from the film with the emulsion facing the light. The light being used is an old Kodak Brownie Darkroom Lamp using a green filter inline with a bulb dimmer. I have a 7 watt bulb inside the lamp. The light is substantially reduced with the dimmer. I cover all luminous dials when doing this. Elimination of stray light is very important. The safelight filter I would imagine could be of most any color if one is using a panchromatic film. I believe that the reason a green filter is so often used is not due to the film but rather due to human eyesight being very sensitive to green light.

    Since stray light cannot be tolerated one must either stay in almost complete darkness for 15 minutes or more or be able to leave the darkroom without stray light getting in. My darkroom is in the basement, completely walled in and has a door that exits into the basement proper. I am not a good candidate to sit in the dark for more than 15 minutes doing nothing. What I do is to latensify my film after night fall. I go into the basement with a flashlight and close the door behind me. I enter the darkroom, close its door and turn on the latensifying lamp and make certain any luminous dials etc are covered. I turn off the flashlight hang the film with the emulsion facing the lamp. I find my way out in almost complete darkness...The latensifying light is no help in seeing where you are going. I exit the basement and come back the same way without any light being...NO FLASHLIGHT.. 30 minutes later. I turn off the latensifying lamp and find the film in the dark and then put it into my paper safe. Lights are turned on and I prepare to go thru my normal developing practices. If I wanted to do this to 400 speed film, I would have to hang the film 24 feet from the lamp...not an option due to size restrictions in the darkroom or reduce the bulbs brightness by a factor of 4 which is easily done.

    If you go thru a bit of effort in testing I believe that you will find latensification a very rewarding practice.
     
  2. Bob Carnie

    Bob Carnie Subscriber

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    Claire

    Would you suggest this method for night photography, I plan to do long exposures with fp4 or trix, develop in pyro .
    Do you think that this method you describe would have the benifit of making the shawdow areas more respondent to development?? hopefully compressing the range from street light to dark shawdows??
     
  3. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Bob--for long night exposures try XR-1. I've been trying to get it to work as a high-speed developer for normal contrast situations, and I haven't been satisfied ultimately, but it does get a lot of speed (about 2 stops of real shadow detail), and keeps contrast relatively low. It didn't work well for what I wanted, but I think it has a lot of potential for night photography. Check out the thread I started here in the B&W Film and Processing forum (search on XR-1 in the title), and the article on unblinkingeye.com for info.
     
  4. Claire Senft

    Claire Senft Member

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    Not a good method for long exposures

    Sorry Bob but if you are into extended exposure times that are sure to require compensation for reciprocity this is likely to be of no help.
     
  5. Claire Senft

    Claire Senft Member

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    A gut feeling

    For high contrast situations that have light sources in them a developer that uses pyrocatchin is very likely to be unbeatable making the bright areas more printable. Ansel Adams has a good illustration of this in his book "The Negative".
     
  6. Claire Senft

    Claire Senft Member

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    Sodium perborate

    Bob one technique that I have used to increase film speed that does not increase contrast is to prebathe the film prior to development in a solution of 1% sodium perborate. I know of no source to buy it. It is however easily made. Go to the drugstore. Buy a bottle of hydrogen peroxide that is used as a disinfectant. This is almost universally a 3% solution. So choose a container 3 time as big as the bottle you bought. Pour into it the hydrogen peroxide. Fill the bottle twice more with water and dump it into the container. You now have a 1% solution of hydrogen peroxide. If, for example, you started with a half pint bottle you now have approximately 750ml of solution. Add to this 7.5 grams of Kodalk or Kodak balanced alklai or sodium metaborate...3 different names for the same thing... you will now have 750ml of sodium perborate. If you are a compounder of developers you probably already have this ingredient. In fact you may also ask your spouse "Honey where do we keep the hydrogen peroxide". Mavbe she will tell you..maybe she will not...have you been nice to her recently?.

    This should give a doubling of speed with any black&white film with the contrast and grain size staying the same. You treat your film for one minute in this solution and transfer it directly to your normal developer without rinsing and develop for the normal amount of time. I use the solution as one shot and discard it. Hydrogen peroxide is fairly useful in the darkroom. it os also used in hypo eliminator...not to be confused with hypo clearing agent. It is extremely effective in eliminating fixer from you photo paper. There is though some concern that it may weaken the fiber base..there are contradictory opiniuons on this matter. If you find that you want to make sodium perborate regularly or hypo eliminator and you live in an area that has a supplier for beauty salons you can buy it in gallons that us much more concentrated and it will be much cheaper for unit volume than the stuff from the drugstore.
    This is as easy as falling off a log. It will reduce any necessity to push film.

    There is nothing as helpful for night time exposure as 15 or more pounds of the stablest tripod you can get your hands on. I use a Majestic tripod. I believe that the only exercise I get is from carrying my gear and coughing from cigarettes..but what else you gonna do when the doctor tell you that you have a tar defficiency?
     
  7. Reinhold

    Reinhold Subscriber

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    Claire..

    Another way to control light intensity is to make a series of "Waterhouse Stops" to fit over the #3 green safelight. I use a Kodak "beehive" safelight (5-1/2 inch ?? diameter), and by experimentation I determined what diameter each stop should be for 125 speed film, 400 speed film, etc.. That way I'm confident that the light output is constant, and that the color temperature of the bulb has not been unduly shifted by reduced voltage from the dimmer.

    Where did you learn about latensification? As I recall, I read about it in an article that David Vestal attributed to Ralph Steiner (Darkroom Techniques, circa 1984???), and have been using it ever since. 35mm, 120/220, 4x5, 5x7, 8x20, Ilford, Kodak, Fuji, it makes no difference, latensification works great. Thanks for reminding us of this little known technique...
     
  8. Claire Senft

    Claire Senft Member

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    Same place you did.

    That photo Tech article is the same source to cover it in detail that I read. I have been wasting film and paper for over 40 years and had heard of it before. Just took me a long time to try it.

    I doubt that changes in color temp would be of much influence. One you have worked out the time and placement it should always work. Although I have not tried it I believe that with pan film it would work with any or no filter if the light's brightness was properly set.
     
  9. dancqu

    dancqu Member

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    Off hand I'd think there would be a conflict twixt
    latensification and pre-exposure. Do you think that true?
     
  10. Helen B

    Helen B Member

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    Very interesting. I've read about it, but never tried it. Now I will. Wasn't it Edmond Becquerel (son of Antoine and father of Henri) who discovered that a latent image in silver iodide could be developed into a visible image with low intensity light? (in La Lumière, ses causes et ses effets, 1868) That's going back a bit before my time so, on this occasion, I'm only passing on what I've picked up from the guy at the end of the bar in the 9th Ave Saloon. Karaoke on Wednesday nights and free popcorn.

    Mason attributes perborate latensification to Vanselow, Quirk and Leermakers: Latensification Studies with Sodium Perborate, PSA Journal, 1948. Peroxide latensification arrived much earlier: 1915?

    How important is it to develop as soon as possible after exposure? How effective is it with highly sensitised films? How does perborate latensification compare to light latensification? Guess I'll have to find out now.

    Thanks again,
    Helen
     
  11. Claire Senft

    Claire Senft Member

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    Perborate Vs light latensification

    Sodium erborate is much easier to use. Pretty fool proff adds about a stop to most films. Load your M6 or M7 put on your prettiest black Summilux. Go out and shoot a roll using two frames per subject...one at your normal speed and one at twice your normal speed and run it thru the prebath. Are the negatives that received half as much exposure, properly exposed? Is the shadow detail in the film that was normally exposed richer than normal. It works with any range of exposure and it is pretty fool proof...it either works or does not.

    Low level light intensification takes greater testing to find the proper amount and duration of light. It requires a really darkroom not a semi darkroom. Patience to wait until the 15 plus minutes have passed is required. It does not work well with exposures of say 45 seconds. Probably work work well with exposures of 1/100.000th of a second either. Where it is usable it can add as much as two stops of sensitivity. Once tested and set up it is easier than dropping a Hassleblad...lot less expensive too.

    I am too deaf to much care about Kareoka, and I am a recovering alcoholic but Helen, dear lady, tell me more about the popcorn at that tavern...is the atmosphere free pf pickled pigsfeet?...Love your photos dear.
     
  12. Helen B

    Helen B Member

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    'Go out and shoot a roll...' thanks to you for the inspiration, I was going to shoot a few rolls. Anything that would need a real dark darkroom would be out of the question for me, so perborate is the thing. I might even find another use for all that peroxide. Can one be a perborate blonde? I need a new 'do' for the NYC Night of a Thousand Gowns in a couple of months. Which reminds me, I should try to get last year's snaps to them before this year's event. A year is such a tight deadline to meet.

    'Once tested and set up it is easier than dropping a Hassleblad...'
    Have you determined that by a repeatable experiment, or is it just supposition?

    ...is the atmosphere free of pickled pigsfeet?'
    Not when I'm there. I wonder if that is just a coincidence or should I change my perfume? Or my socks?

    Thanks very much for the kind comment on my snaps. I'd love to see some of yours.

    Best,
    Helen
     
  13. Cheryl Jacobs

    Cheryl Jacobs Member

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    I hate being ADD. I can't get past the first five sentences of the first post..... I just glaze over......
     
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  15. Claire Senft

    Claire Senft Member

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    once was enough

    I did not have to do the experiment with a Hasselblad a second time. I was convinced without having to do it 24 more times to achieve a high statistical probability...my apologies to Deming and Taguchi. Helen I am willing to bet that perborate, if you wished, could make you the fastest blond in either NYC or Lonum town but I conjecture that you could never be overexposed. My faith in you is so complete that should I be able to borrow $.25 from my spouse I would bet it all on you. Alas, I have insufficient collateral to establish a line of credit exceeding a nickle with anyone that knows me.

    Cherly do worry about it just keep using that Bronica so well.
     
  16. dancqu

    dancqu Member

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    Fb+f, somewhere around 0.10 or a little more in density? I seem
    to recall having read of a post-exposure technique applied to an
    entire roll of film; very similar to what you describe. I recall
    nothing about such long exposures.

    Off hand I'd think the result would be the same, pre or post
    exposure; pre-expose then shoot or shoot then post-expose.
     
  17. Helen B

    Helen B Member

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    I wonder if the difference is something like this (in a very simplistic manner):

    The post exposure occurs at such a low intensity that it would be unable to cause much fog: the rate of creation of silver atoms is too low for them to be stable unless there is a latent sub-image centre (with two atoms, so more stable than a single atom, but probably undevelopable) to join onto and thus become stable. Therefore post exposure low intensity light is able to add atoms to fairly stable sub-image centres and turn them into developable image centres.

    Now that's probably not the real truth. I think that it is way more complicated than that so just look on it as a diagram, as an architect might say.

    Pre exposure flashing, at least the version that I'm aware of, works in a different way, at a higher intensity.

    How does that sound? It might all be nonsense - it's late and I'm weary.

    Best,
    Helen
     
  18. fhovie

    fhovie Subscriber

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    I will try the perborate! - I don't understand the difference in results between the latensification listed above and simply preflashing.

    I really love apug .... where else would you learn all this stuff!!!
     
  19. MurrayMinchin

    MurrayMinchin Membership Council Council

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    Um...excuse me Claire, Helen & Cheryl...got a kick out of your banter back and forth!

    I think I'm following you regarding the "awakenings" of silver crystals that had received just below the number of photons needed to become "viable", and therefore unable to be developed into usable shadow texture. If I'm wrapping my head around this properly, wouldn't this work in any development situation ( -1, -2, +1, etc)? Wouldn't it only ever effect the lowest tones?

    As an alternative couldn't you instead give -1 SLIMT (David Kachel's method) and +1 development & get the same effect without being subjected to complete darkness for 15 minutes? (Although this might only work for Normal development?)

    Interesting for sure!

    Murray
     
  20. Claire Senft

    Claire Senft Member

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    ANY n LEVEL

    Once you have established a suitable normal condition of time and intensity for a film at an elevated speed due to latensification with light you can work out N+ and N- conditions. However, since you are increasing film base fog very extended development will also raise fog levels here as extended development does without latensification. In other words additional testing of the latensification and subsequent modification may be in order so that you do not get grossly inflated fog levels. N- should not be as much of a concern.

    With the perborate I would not worry about using it effectively with N+ and N- times. If a film that you have used will give you the following without perborate are for example n-2= 40, n=64, n+2=100 and you find for a normal ...N... condition with perborate you get 125 film speed then your N-2 should be 80 and you N+2 should be 200. Should work very nicely. Not all films are going to give you exactly 1 stop increase. I do not use a wide variety of films. I buy Tech Pan...at least until now and 100TMax in 100 foot rolls. Although I have a nice 6x7 camera with 4 lenses I work almost exclusely in 35mm.

    This is a suggesstion for those that use 35mm and want to work with the zone system or BTZS techniques in 35mm...it is what I do. Buy your film in bulk. A 100 foot roll is the equivalent of 18 36exposure rolls. I but 100TMax from B&H...the imported version.. for about $27.00 including freight to Milwaukee. I load 6 exposure rolls..enough for 6 exp+leader. I set up my tripod and make 4 identical exposures with ..or without a particular filter and then 1 exposure with a filter that seems to have possibilities and 1 exposure that seem not likely to be useful. If the first 4 exposures were with a filter then 1 of these last 2 will be without a filter. By taking for indentical exposures I have protected myself from negative damage. And I have developed real life experience in finding proper filter factors for my film and conditions I use it under. Having done the foregoing I develop my film for the subject brightness range that existed at the scene I do not know if I am a meticulous person. I am more likely tedious. As a child I was always instructed "If a thing is worth doing, it is worth doing well". I fear that I have corrupted this into "If you are going to do something, be sure you make a big production out of it."
     
  21. Ole

    Ole Moderator Staff Member Moderator

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    Off topic here, but that developer was Windish' Compensating Pyrocatechin. There is an even better illustration in "Die neue Foto-Schule" - by Hans Windisch. I have tried it on negatives from a solar eclipse, and it really does deliver details both in the shadows and highlights - even when the highlight details were sunspots!
     
  22. dancqu

    dancqu Member

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    It is less a bother to post-flash, latensify, an entire roll of film
    than to pre-flash an entire roll of film. May be that goes for
    sheet film as well. Dan
     
  23. dancqu

    dancqu Member

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    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
     
  24. Helen B

    Helen B Member

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    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.

    Best,
    Latent Sub-Helen
     
  25. MikeS

    MikeS Member

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    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?

    -Mike
     
  26. gainer

    gainer Subscriber

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    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.