Pre-exposing film for decreased contrast ? : LUSENET : Large format photography : One Thread

For the most part I shoot primarily in heavily wooded areas, often in bright sunlight with deep shadows. I prefer to create images with bright open shadows, so I am constantly fighting against high contrast. Up until now I have been primarily concentrating on film compensation development and latent image bleaching to help create the images I seek.

However, over the years Iíve read about, but not tried, the technique of pre-exposing sheet film prior to field exposure, presumably to decrease overall contrast of the film (AA ďThe NegativeĒ p119-123). Iím not excited at the thought of discovering yet another way of destroying film, I already have quite a few successful methods already :-)

So I am interested in hearing from anyone that uses this technique, your successes or failures, or any tips you might have that would help me.

TIA - doug

-- doug mcfarland (, January 28, 2001


It works fine. The basic idea is that if Zone II has 2 units of light and Zone VII has 64 units of light, a uniform 'fogging' exposure of 2 units will add 2 units right across the scale. The difference is that Zone II gets elevated to Zone III (2 units from scene plus 2 units from fogging exposure) but Zone VII hardly shifts at all (64 + 2 =66 units).

The fogging exposure can be made before or after the main exposure (so, if you can keep your film seeparate in the field, you can always add the extra exposure in your darkroom). You can use either your enlarger or a pre-exposure device which is essentially like a diffusor or you can fill the frame with a grey card and expose it to the grey card. Essentially, what you end up with is a deformation of the characteristic curve by lengthening the toe. You get similar deformations of the curve from flare.

The downside is that you lose local contrast in the shadows. That is, you hold a longer scaled subject but the local contrast in the shadows decreases (since lengthening the toe basically reduces the slope of the toe part of the curve). I guess its an individual aesthetic decision as to when you would use it. I would suggest this as a tool to use when you need to hold a longer scale but local contrast in the highlights is crucial.

Your goal of open, luminous shadows suggeests this is an area of crucial local contrast. However, a lot depends on how you visualize it. Shadows can be open and luminous but soft, which suggests a reasonable placement (fairly high on the toe) and something like a fogging exposure. Or they can be open and luminous but quite hard, in which case it could be a fairly high placement (to move the shadows off the toe) and compensating development.

Hope this helps. DJ

-- N Dhananjay (, January 28, 2001.

How about giving a compensating development process like split D-23 a try. I too shoot in high contrast situations and this developer allows me to read my shadows, place them around zone 4 and still not block up the highlights.

-- William Levitt (, January 28, 2001.

Why not try the same thing but with your print. Flashing the paper to bring it up to the exposure threshold is easy to do. Just experiment with the exposrue times to get the level of detail in the highlights and then print for the standard time. Paper is alot less expensive to work with than film. Alot faster, too. Thats my two cents.

-- Doug Theall (, January 28, 2001.

Polaroid used to send a diffuser with a close-up attacment kit no.583. You could probably find one for almost nothing on ebay if you're the adventurous type. It is a white plastic diffuser with 3 little ears that, as luck would have it, will cling to a 67mm filter. In those situations you're referring to, if I remember which is the hardest part, I put the diffuser over the front of the lens and adjust the aperture to expose for zone II. Then take it off and resume the pic with my normal exposure. For starters try doing it both ways on the some pic in the same film holder to see if you like the difference. 1 as normal, and 1 with the diffusion fog added.

-- Jim Galli (, January 28, 2001.

As I noted in my lengthy question, Iím using a lot of techniques after the film has been developed. I use graded paper and use general overall flashing quite often, more recently latent image bleaching, and also compensating film development. I used to use D23 but didnít like the overall results. Now I process in PMKpyro which is not recommended for compensating development, but Iím experimenting with a new technique for development (err should I say destroying film :-)

I hadnít considered post-exposure film flashing. Since I usually shoot two plates, I could develop one and then consider the alternate plate for pre-development exposure.

thanks - doug

-- doug mcfarland (, January 28, 2001.

It makes no difference whether you preflash or post flash your film. The poster who suggested flashing your paper makes a point, BUT, the downside is you have to test the paper with a series of flashes (while taking notes) in the darkroom to determine correct exposure. With film, you know the speed, and if you've made a light reading, you know exactly how many stops to close the lens down to reach a zone II exposure. Moreover (this is the important bit), flashing PAPER is helful to tame PAPER contrast, not FILM contrast. In other words, flashing the paper will not give you shadow detail that is not ALREADY recorded on the film. If you want to record additional shadow density on film, then flash the film, or it's pointless. The advantage to this is two-fold: you "get it in the negative," which means you don't have to flash every damned piece of paper from here to eternity, and you've got a negative with a long tonal range, which can be suitably printed on various grades of paper for different contrast renditions. The best, best, best, friend to the photographer, with regard to this issue, is Ansel Adams' book "The Negative." If you consider yourself a photographer, you should have it on your shelf. . it will obviate several trips to for what is sometimes conflicting advice:))) Also, Adams is ALWAYS right on technical issues, so you can be assured that if you follow his advice, you will have mastered your technique.

-- Josh Slocum (, January 28, 2001.

IMPORTANT!!!!!! I forgot the most obvious thing!!!!! Flashing the paper increases HIGHLIGHT DENSITY in the print, not shadow!!!!! Flashing paper in the darkroom will have no effect on your shadows at all (remember we are dealing with a negative tone process here), so my original point on film flashing stands. For notable examples of what flashing can do, watch "Evita" (only one example). The DP flashed the film with several warm shades of yellow, which gave the effect of filling in the shadows with warmth and body to match the South American evening light he was shooting in.

-- Josh Slocum (, January 28, 2001.

Thanks for the notes Josh - I didn't think about the long term advantage of having a better shadowed negative as opposed to always fighting with contrasty negative printing-after-printing.

Also you mentioned AA's book "The Negative" - I referenced that in my original question - I'm never without it, and a 1/2 dozen other high quality books as well :-)

I also like the suggestion of a field diffuser that would clip to the lens.

I knew this forum was a good place to post this sort of question.

Thanks Doug

-- (, January 28, 2001.

Regardless of whether you can see much difference in the negatives, there is a big difference between pre and post exposure. Pre-exposure brings the film up onto the curve already, basically getting ready for exposure in dim areas without them being off the bottom of the scale. It might be thought of as "presensitizing" instead. What would have been too low to record is now exposed at a level on the curve where it can be captured. Post exposure will do nothing to move the original subjects higher on the scale when they are exposed. They may fall too low and will not register, then you add blank density over that. Why? The idea is not just to fog the film, it is to make it more receptive to what light there is available. However, when you have to print through the fog, there may not be much of difference, so it may appear similar. They idea is different, though.

-- E.L. (, January 29, 2001.

With regard to pre versus post exposure, there is no difference, in senitometric terms, between flashing before or after the main exposure. Presensitizing or hypersensitizing is another technique altogether wherein you bake the film in a gas (usually a combination of hydrogen and nitrogen) to increase its sensitivity. A related technique, often referred to as latensification i.e., latent image intensification, involves making the least developable grains hit by light developable. This is done after exposure but before development by exposure to peroxide (if I remember correctly).

As far as flashing goes, there is no difference whether the flash comes before or after the main exposure. What matters is the total quantum of light that hits individual areas of the negative and the 'fogging' flash basically will increase the responsiveness of the grains to the main image light by overcoming some of their inertia i.e., by moving them up to the toe point in the curve. This happens even if the flash occurs after the main exposure ie.., the main exposure records parts of the image on the curve and parts below in proportion to light refelcted from the scene. Additional light serves to move all of them up the curve. This can be tested by exposing two photographic papers or films to a step wedge, one with a flash before and one with a flash after. There should be no difference in fog densitiy and density of each step. Cheers, DJ.

-- N Dhananjay (, January 29, 2001.

Here's a place that sells a nice diffuser to use for this purpose:

-- Chuck Pere (, January 30, 2001.

An illustration how a pre-exposure modifies the film curve, assuming the initial film curve (in black) was a straight line with contrast=0.5:

The values in brackets show the amount of pre-exposure.

Regards, Andrey

-- Andrey Vorobyov (, February 01, 2001.

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