View Full Version : pre exposure

John Berry ( Roadkill )
31-Oct-2005, 09:00
I have a shot that needs pre exposure. I did a search of the forum and didn't find anything about the way I'm thinking of doing it. I was wondering if anyone has used their enlarger to pre expose film? My thinking is I would be able to establish a constant value that I could adjust as necessary. Thanks, John

steve simmons
31-Oct-2005, 09:03
Why do you think your film needs pre-exposure?

Is it color trans, color neg or black and white?

steve simmons

31-Oct-2005, 09:23
Pre-exposure is simple. You figure out the exposure for the scene, then shoot the film at one-thirty-secondth of the calculated speed or close down four stops. Place a gray card in front of the lens and defocus so there is no detail. Expose the film to the card, then expose the same film to the scene with the normal exposure time. The idea is that you are pre-flashing the film in order to subdue the highlights. This might be useful when for example, shooting a shaded object against the sky.

George Stewart
31-Oct-2005, 09:41
I thought of doing the same (never had a chance) with my enlarger for some LF astrophotography. I think the best thing would be to do some test strips (with film) having the lens stopped-down and see what exposure gives the slightest hint of fog. Also baking in the oven might enhance the film a bit. The Kodak web site should have some info on sensitizing film with preexposure and baking.

Doremus Scudder
31-Oct-2005, 10:28

The idea is to pre-sensitize the film so that the slightest exposure will then register as shadow detail. This has the advantage of allowing some contrasty scenes to be shot without contrast reduction in development/printing, however, it does reduce the separation in the lower zones, i.e. reduces detail and separation in the shadows. Flashing paper when printing is what you can use to tone down the highlights.

I have found that the loss of separation in the shadows when pre-flashing is just not worth the trouble with black-and-white. Conventional Zone System contraction techniques do almost the same, and, if you use compensating development or SLIMTs when making the contrast, much more detail is kept in the shadows.

With color film (transparency especially), pre-exposure can be a valuable tool. The proper technique is described above: focus on your subject, meter a gray card and expose on Zone II (for transparency film) or Zone I for negative film. Make sure the lighting is constant.


John Berry ( Roadkill )
31-Oct-2005, 14:06
Thanks for the answers. I'm shooting fp-4 and developing in pyrocat semi stand. I have one scene that I have shot that has mountains with snow in sun and deep shadows on the shadow side of the river. I was thinking in term of preflash in stead of N++ or N+++ development. N+ didn't do enough. I'm thinking to much N+ might flatten out the neg too much. Other than the deep shadows everything else in the shot is about the way I want it. Thanks, John

John Berry ( Roadkill )
31-Oct-2005, 14:58
correction, N- instead of N+

Richard Schlesinger
31-Oct-2005, 16:38
As with nearly all questions photographic, Ansel A. dealt with this in his book "The Negative". As I remember, you should point the camera, focused on infinity, at an evenly illuminated piece of illustration board or something similar. Totally outof focus. Then, give a Zone II, more or less, exposure, depending on how much density you want. If you have done film speed tests and checked the timing on your shutter this will give you a nice over all pre-exposure - practically no effect onthe high values but will add significantly to the low ones. Takes care of the excessive contrast.

chris jordan
1-Nov-2005, 05:52
I've used this technique quite a bit, especially with chromes. Actually, what I do would be termed "post-exposure". It is adding the extra exposure units to the already-exposed film, thereby "bumping" tonal values that are just below the threshold over the top, into the visible range. You do the same thing, but add the "sensitizing exposure" afterward. It is doing the same thing. Post exposure has the advantage that you can decide after shooting which chromes require it and then leave the rest alone. I shoot a gray card, throw it out of focus as mentioned, and add I-II zones of exposure. You should run tests. I've found a slight loss of color saturation, but not enough to worry about. I find this technique very fun in an "alchemist" sort of way. Good luck,

CJ Chris Jordan (Troy)

Hans Berkhout
1-Nov-2005, 06:25
instead of a (grey)card I use a Wallace Expo Disc in front of the lens, like a filter. First meter throught the disc, that's z. V.

ronald lamarsh
1-Nov-2005, 19:25
I jsut got back form a workshop where the was discussed and it seems that one would be better off just placing the shadows higher up on the scale. Why? because even a Zone 2 pre=exposure doesn't get you up off the toe of the curve enough to provide the separation need.

james mickelson
2-Nov-2005, 10:14
I have found that using a piece of white acrylic (as opposed to a grey card which muddies the color) in front of the lens gives me nice shadow detail on chrome at zone I without desaturatinbg the color and leaving the highlights where they are normally. I also use this when shooting black and white emulsions. This pre-exposure works well when coupled with preflashing the paper as well. Normal film exposure and processing together are useful tools in anyones toolkit. Each tool has it's place and value. I suggest learning them all. I find with color positive materials that pre-exposure works great when exposing near dark in the morning and evening twilight. Instead of just getting the color in the sky you can also get some shadow detail in the foreground as at Mono Lake.