I have preflashed film on Zone III and IV at times when I have had extreme brightness ratio situations. (14 zones).
Preflashing at that high a level will compress the high brightness ratios to a point where I can print the negatives with no further corrective actions at the printing stage.
Preflashing compresses shadow values whereas flashing of paper at the printing stage compresses highlights. I prefer to compress shadows because most people expect shadows to have less tonal separation.
If one were to uniformly expose a second negative at that high a level and sandwiched it with the camera negative at the printing state it would manifest itself as uniform density. Preflashing is proportional in it's effect.
Pre-flashing film is an old technique used by news photographers in the days of the Speed Graphic. By exposing the film to an amount of light equal to Zone I or II any additional light, howver slight, will record. This in effect adds exposure in the shadows. This small amount of light has a very minimal effect on the highlights.
At one time this was said to increase the film speed. It does not do so, it merely adds exposure where it is needed most - in the shadows.
Today I frequently use it when photographing against the light to open up the shadows without blowing out the highlights.
"Preflashing is proportional in it's effect."
That's the part of this whole thing I don't understand, Donald. Why wouldn't the sandwiched neg also be proportional? If you preflash film at higher zones, say zone 3, that exposure is added to the highlights as well, though it represents a proportionally lower addition to their densities. Why wouldn't a sandwiched negative also not add to their densities at a proportionally lower level?
I don't mean to beat this horse, it's just that I find it an interesting question and would like to understand the theory.
I have given this more thought and I see where you are approaching this from. I also understand the basis of your question. You pose an interesting question and I had never considered this before. It appears that when I apply mathmatical values to the two methods that the effect should theoretically be the same, now that I think about it more.
If someone were to uniformally expose several negs at differing low density values these could be used in the darkroom as effectively as pre-flashing the film at time of the exposure provided the conditions that I next mention have been satisfied as well.
The thing that may be lacking in your approach would be the potential for inadequate low value camera negative exposures. Additionaly, if one were to adequately expose shadows, in high brightness ratio situations, then the potential exists for placing the highlight values on the shoulder of the film's characteristic curve. Both of these potential problems would be eliminated by preflashing the film in camera at time of exposure.
For instance, in high brightness ratio situations, when I pre-flash film at Zone III or Zone IV values, I will make my exposure determination for the second exposure based upon highlight value placements and not meter readings based on shadow values.
I think that an unsharp mask would provide the same effect of reduction of density range and additionally provide enhanced apparent sharpness due to edge effects...although an unsharp mask would necessitate making a mask on a case by case basis.
Have you tried the approach that you have suggest? I would be interested to learn about your results. Thanks...
"differing low density values these could be used in the darkroom "
That was my idea....
"the potential exists for placing the highlight values on the shoulder of the film's characteristic curve"
....and that was one of my concerns, at least initially. But shoulders are a function of a *single* negative's response to high exposure and since the additional "exposure" (density, really) in this case would be by way of the sandwich negative, it should simply be additive without shouldering out. How the paper handles it is another matter.
It really is something to fool with experimentally in the coming cold weather.
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I'll make it easy. Use "differing low density" ND filters
Originally Posted by Poco
within the enlarger or under the lens. If you have positive
results, film pre-exposure can be dropped in favor of dial
it in when the printing is to be done. Dan
It's not the density that does the trick, you are confusing cause and effect. Its the added light to the shadows that bring out the detail inherent. Film has a threshold level below which exposure generates no density. The flash exposure combines with the image exposure to jump that threshold and make image detail where none was. Adding film density after the film is developed is pretty much wasted effort, as you haven't got that shadow detail to do anything with.
Originally Posted by glbeas
I agree with your assessment about bringing the exposure to a threshold...however I disagree with your position about additional density accomplishing nothing. When I preflash at a zone III or IV value for a scene brightness ratio of 14 stops then the additional density beyond a "trigger exposure" serves to compress the 14 stop range.
Additionally if the film is properly rated then a preflash at a Zone I or II exposure value will be represented as density on the camera negative.
Theoretically, taking Poco's hypothesis, it would make no difference if the additional density beyond a "trigger exposure" was added in preflash of the camera negative or in a second neutral density negative added to the camera negative and printed as a sandwich of the two. The effect would be to compress the density range of the negative.
I have given this more thought and I see where you are approaching this from. I also understand the basis of your question. You pose an interesting question and I had never considered this before.
No doubt I'm being thick here, but I do not. I understand "classic" preflashing in the sense of filling in the toe, but what does the original poster mean by "sandwiching"? Is this at printing, in camera (pretty snug filmholder, that)? What is the reasoning behind it?