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