Pre-flash vs pre-exposure. Whaaaaaat?

pbromaghin

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Looking through Flickr at examples of Harman Direct Positive Paper, I came across a photographer who said

" I do pre-exposure, with few stops down which is something similar to pre-flash. Otherwise the pictures turn out to be too-contrasty. "

I get the pre-flash thing and am setting up a space to do it, but what the heck is this pre-exposure he's talking about? He shows some of the best examples of the paper's use in landscapes, so he must be doing something right.
 
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pbromaghin

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Ummm, I know. I started that thread.

My intent here is to have a discussion about pre-flash vs pre-expose in general, not just how it pertains to HDPP.
 

Vaughn

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Well, He is pre-exposing the positive paper primarily in the highlights (not enough exposure to affect the shadows) -- which will darken the highlights relative to the shadows. Then a regular exposure after that...makes sense. It would increase contrast with negative material.

I knew a fellow who was experimenting with pre-exposed transparency film along the same lines -- several decades ago, I can't remember how successful he was. He was also trying this thru a color filter to reduce the blue cast in the open shadows.

Edit: Delayed memory: Actually, I believe he was actually flashing the film before exposure thru a filter, not pre-exposure -- pointing the camera at the sky, out of focus (in case of bird and planes), and giving the film a little flash of color, then compose the image w/o the filter and expose normally.
 
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pbromaghin

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Vaugh, thank you. But just what is a pre-exposure and how does one actually do it compared to doing a pre-flash?
 

pentaxuser

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pbromaghin said:
Vaugh, thank you. But just what is a pre-exposure and how does one actually do it compared to doing a pre-flash?
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Yes, Peter, I haven't quite worked out what the difference is either nor the difference in routes needed to achieve each.

pentaxuser
 

MattKing

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Pre-exposure could refer to making two exposures on the same sheet of the same scene, with one exposure being a lower intensity one.
I can't think of any good reason to do that.
 
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pbromaghin

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Matt, the guy does write that the pre-exposure is a couple stops less than the real one. However, there are some people in one of them and they don't look ghosted or anything like would be expected in multiple exposures.
 

Andrew O'Neill

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For me, pre exposure is exposing the film to non image forming light to zone 1 or 2, with a translucent piece of plexiglass over the lens, then removing the plexiglass and exposing that same frame to the subject. It can work quite well due contrasty scenes. With negative film it boosts the density in the shadows. It's the opposite with outsource film.
 

Vaughn

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pbromaghin said:
Vaugh, thank you. But just what is a pre-exposure and how does one actually do it compared to doing a pre-flash?
Click to expand...
Pre-exposure uses the light from the scene to selectively expose the film. Flashing uses (normally) an even exposure over the whole sheet.

Flashing works by bringing the paper or film up to the threshold exposure it needs to react to light and show a tone. Thus just a little more light during the regular exposure will thus create a tone. With negative material, this means that little bit of light making it through those dense highlights will create a tone, rather than not being strong enough to push the paper past that threshold.

Pre-exposure on the other hand (exposing the same scene at a lower exposure to record only highlight values) works at a much higher light level and can more radically change contrast.
 
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pbromaghin

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Which leads to another question - How does one use the light selectively?
 

Vaughn

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Pre-exposing can record just the highlights, or highlights and upper mid-tones -- that is pretty selective. But I am beginning to wonder about the effectiveness of it all. It has been an interesting mind experiment -- now I am wondering if I have gotten off the tracks a bit. Since the first exposure (pre or whatever) has no filtering effect, the pre-exposure just adds a touch of time to the main exposure unless the shadows receive no significant exposure (not enough light to even strike silver). However, use some filtering of some kind to the first exposure, then the effect can be greater.

I use filters to selectively use light by its color...I use a yellow filter in the redwoods in the fall for the yellow leaves -- gives a pop to all that yellow light.
 
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Doremus Scudder

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Vaughn,

Pardon me if I'm being a bit dense here, but I can't see where "pre-exposure," as you describe it, followed by a "normal" exposure of the same scene is any different than additive, intermittent exposures. Sure, you can use different filters for the two exposures (helpful with color transparency materials) to balance out the shadows, but you're not going to get any contrast reduction/increase other than that introduced by the filtration and the intermittency effect (similar to reciprocity failure). Please correct me if I'm wrong. Also, I don't see where this practice would be helpful in reducing contrast with a black-and-white reversal material...

In my parlance, I use the terms pre-flashing, flashing and even overall pre-exposure to mean the same thing: giving film or paper a small, even exposure to affect contrast by bringing the material closer to threshold exposure, which affects the densities in the least-dense areas of whatever material is being used. This would be what I'd use for controlling contrast, not pre-exposure as you describe it.

Please enlighten me if I'm overlooking something here.

Best,

Doremus

[Edit: I see you've arrived at the same basic conclusion as I have. I imagine the question posed by the OP is moot really, with "pre-exposure" and "pre-flashing" simply being used interchangeably to describe the same thing.]
 

Vaughn

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I think my last post answers that.

But again -- The matter in question is someone 'pre-exposing' positive paper in-camera to reduce contrast. A film/paper's threshold is based on the idea that it takes a certain numbers of photons striking a silver salt ion (term?) to 'expose' it enough to be acted on by the developer. There is a slight lag in response to light is areas of very low exposure until the silver is exposed enough -- causing reciproisity failure at very low exposure rates.

So, can the exposure be low enough so the paper does not even 'build-up' an exposure, and thus have no effect in the shadows in the main exposure? (edited to reduce my confusion).

As I said -- thought experiment
 
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