Is pre-exposing negs a useful tool or a complete waste of time?

[sdotkling]

Hold on. What the hell is "pre-flash"? Are you talking about exposing film before you ...expose the film? How exactly are you doing this?

 

[Bruce Robbins]

Thanks for all the great replies so far. Is it fair to sum them up by saying there's a consensus that pre-exposure does work as Barry Thornton and Ansel Adams say but considerable doubt as to how effective and, therefore, useful it is? On that basis, perhaps Barnbaum and Thornton/Adams are all correct to some degree?

 

[DREW WILEY]

Barnbaum makes lovely prints but kinda gets in a stuck-record formulaic mentality sometime. That's fine; but there's more than one way to skin a cat. Adams' tool kit was fairly primitive. For one thing, VC papers weren't all that good during his lifetime; and he never seriously
explored masking, both of which offer much better control than flashing. No big deal. Try it and see if you like it. I don't.

 

[Rudeofus]

Can it improve shadow detail, no. Shadow detail depends on exposure. You cannot "trick" the emulsion into registering what is not there.

The proof of the pudding is in the eating, and Athiril has shown some incredible pudding here in this thread, and more in the color chemistry subsection.

We have good reason to believe, that after weak exposure some silver halide grains contain a stable but undevelopable silver atom cluster. A preflash can provide just enough of these tiny silver clusters, that this weak exposure can turn them developable silver clusters. I would be not at all surprised if we could gain a few stops in real sensitivity, at the expense of spectacular grain in the shadow regions, i.e. substantially less enlargeability.

 

[Xmas]

Hold on. What the hell is "pre-flash"? Are you talking about exposing film before you ...expose the film? How exactly are you doing this?

Yes exposing before hand is one way of preflashing the silver halogen sensitive centre so that it will be developed to a silver grain.
A post flash should also work in theory.
Flare should also work in theory.
You needed to do this when duping transparencies even on to duping transparency film to lower contrast.
It is optional but will still work otherwise with other silver halogen processes, including mono negatives.

 

[Xmas]

Thanks for all the great replies so far. Is it fair to sum them up by saying there's a consensus that pre-exposure does work as Barry Thornton and Ansel Adams say but considerable doubt as to how effective and, therefore, useful it is? On that basis, perhaps Barnbaum and Thornton/Adams are all correct to some degree?

No more simply it is a tool like an impact wrench and butane torch for removing galled nuts that purists don't like.

 

[DREW WILEY]

I wouldn't classify it as a silver-bullet niche tool like an impact wrench. I sell all kinds of impact wrenches, so know the difference. Flashing
is more like trying to remove a stubborn bolt with a rusty monkey wrench dredged off the bottom of an estuary. It will kinda work, but probably not as efficiently as you hoped.

 

[msage]

Having read your article in your blog I would just coment that Adams and Thornton and I think Barnbaum all advocate exposing for the shadows and developing for the highlights.
So why are they all espousing a technique which is exposing for the highlights and then trying to fix the shadows by pre-flashing film?:

Different techniques give different results.

 

[Gerald C Koch]

The proof of the pudding is in the eating, and Athiril has shown some incredible pudding here in this thread, and more in the color chemistry subsection.

We have good reason to believe, that after weak exposure some silver halide grains contain a stable but undevelopable silver atom cluster. A preflash can provide just enough of these tiny silver clusters, that this weak exposure can turn them developable silver clusters. I would be not at all surprised if we could gain a few stops in real sensitivity, at the expense of spectacular grain in the shadow regions, i.e. substantially less enlargeability.

Yes, but the results are rather unpredictable and depend on several factors. This seriously limits what can be done. This is why I mentioned Dr Henry's book Controls In Black And White Photography. If you want increased film speed then this is best done outside the camera using a very weak and controlled light source. The process requires several minutes and is not really pre-flashing.

Technically there are two separate terms hyper-sensitization and latensification, quod vide. Of the two hyper-sensitization is most often used and is routinely used by astronomers.

 

[nosmok]

Back in the Plestiocene era when I was in film school, everybody who was editing their films always wondered how come the flash frames at the end of the shot looked so much better than the rest. However, not even the tech heads tried to pre or post flash to get at that look in a controlled way. Yes it works, especially well for color. But depending on circumstances, probably more trouble than it's worth.

 

[Xmas]

I wouldn't classify it as a silver-bullet niche tool like an impact wrench. I sell all kinds of impact wrenches, so know the difference. Flashing
is more like trying to remove a stubborn bolt with a rusty monkey wrench dredged off the bottom of an estuary. It will kinda work, but probably not as efficiently as you hoped.

I'd concur but any gain is a gain, and all I do is use a single coated lens on sunny days swapping a lens is easy.

And I use each of an impact wrench, butane torch and shock and unlock liquids, to undo galled parts.

 

[Jim Noel]

It is easier just fitting single coated lens.

It is also easier to just ask and accept the answer rather than doing a little research, and/or experimentation.

 

[Jim Noel]

Hold on. What the hell is "pre-flash"? Are you talking about exposing film before you ...expose the film? How exactly are you doing this?

Method #1 as used by freelance news photographers up into the 1950's or 60's - LAy the film out in the darkroom and expose it to a very small quantity of light. The load it in the holders ready to go. In very dim light it effectively raised the film speed because the film was already exposed just to the edge of the film's sensitivity. A normal exposure then produced images with detail in the dark shadows without increasing the density of the highlights.
Method #2 as used by a lot of us today. When a scene is encountered in which the contrast is too high making it difficult to have detail in important shadows w/o blowing out the highlights use a translucent colorless object, like a styrofoam coffee cup. Meter through the cup and determine the exposure for ZOne I, or in some cases II. Make suchan exposure through the cup. Remove the cup and expose the film as indicated by the meter, or the photographers knowledge.

Develop normally.

 

[DREW WILEY]

Xmas - customs are quite different in certain countries. The Italians still often cement threaded air fittings in with shellac. That used to be done in the old days here using something called Indian Head Shellac. But now we use Teflon tape or things like Rectorseal. If people don't
know that you have to heat the Italian fittings, the darn things usually break before they'll unscrew. The type of wrench won't help much.
Gotta have a heat gun in the shop too.

 

[DREW WILEY]

And your other comment, XMas.. Yeah, I sometimes like to fine-tune contrast by owning more than one lens in the same focal length, but
single-coated vs. multi. It's more helpful to me in color work, where fine-tuning the contrast has a greater net effect than in black and white.
But sometimes a bit of deliberate flare is nice in certain parts of the scene, to impart a more atmospheric sense or whatever. What I don't
like is veiling flare - an annoying symptom of flashing if overdone.

 

[Gerald C Koch]

The following should be of interest to avoid comparing apples with oranges.

http://en.wikipedia.org/wiki/Photographic_hypersensitization

Pay particular attention to the following quote.

Preflashing is not strictly a hypersensitizing technique.

 

[Athiril]

All that pre-flashing does is to move the image further up the characteristic curve. Is this useful, depends on what you are trying to do. As a general purpose tool it is a waste of time. Can it improve shadow detail, no. Shadow detail depends on exposure. You cannot "trick" the emulsion into registering what is not there. I cannot get to my copy but what does Dr Henry say on the subject in his book?

It improves shadow detail and I have the negs to prove it. I've exposed without pre-flash and with increasing pre-flash, on the same roll in the same developer and developer time, they're all the same until all of a sudden, there is a sudden jump in density, shadow detail and contrast.

I don't expect B&W film to be an exception to this, especially since I modeled the test after what is said about newspaper photographers doing exactly the same with Tri-X back in the for increased shadow detail.

It isn't pushed up along the scale of the neg, especially since I ended up scanning the film with a high end scanner and simply could not pull out those details which were not present on the neg, but are on the pre-flashed one. It requires a heavy push to achieve iirc.

The proof of the pudding is in the eating, and Athiril has shown some incredible pudding here in this thread, and more in the color chemistry subsection.

We have good reason to believe, that after weak exposure some silver halide grains contain a stable but undevelopable silver atom cluster. A preflash can provide just enough of these tiny silver clusters, that this weak exposure can turn them developable silver clusters. I would be not at all surprised if we could gain a few stops in real sensitivity, at the expense of spectacular grain in the shadow regions, i.e. substantially less enlargeability.

You can also consider it like this, if x is the lowest recordable exposure level on the film - including in the push. Then obviously x/2 wont be recorded, with a pre-flash of x/2 it'll push up to x, with a preflash of x it'll push it up to x*1.5, etc. I'm not saying x is where we pre-flash exactly, perhaps it is between the toe and straight line portion and the push stretches the contrast out. Just a thought experiment.

I don't see it as as less enlargeability if you compare it at the same exposure, the one without is substantially worse off and far less usable of an image. Compared to simply using the film normally at it's rated speed then, yes substantially less enlargeability.

 

[Gerald C Koch]

You may see an increase in shadow detail but it is not due to increased film speed. If you intensify a very thin negative you will see more shadow detail but you have obviously not increased the film's speed. You have just increased the visibility of the detail. Hence the quote from the article in my previous post.

Years ago before the invention of VC paper some photographers would only stock grade 5 paper. Then by pre-flashing they could reproduce any of the lower grades. It saved the expense of stocking many grades and gave the ability to produce fractional paper grades.

 

[Xmas]

You can also consider it like this, if x is the lowest recordable exposure level on the film - including in the push. Then obviously x/2 wont be recorded, with a pre-flash of x/2 it'll push up to x, with a preflash of x it'll push it up to x*1.5, etc. I'm not saying x is where we pre-flash exactly, perhaps it is between the toe and straight line portion and the push stretches the contrast out. Just a thought experiment.

I don't see it as as less enlargeability if you compare it at the same exposure, the one without is substantially worse off and far less usable of an image. Compared to simply using the film normally at it's rated speed then, yes substantially less enlargeability.

While the preflashing lifts the toe sensitivity it won't make any detectable difference to shoulder? Even using your plastic cover technique.

When Cosina were marketing M lenses for the Bessa they tried a 40mm /1.4 supposedly the BWC Mr K liked 40mm,
But they made two initial batches in each of single SC and multi MC coating.

They anticipated the SC would be a panic buy only for the Ja mono freaks but found it sold as well as the MC to the USA and EU.

When you use a SC the light for the shoulder is reduced and sprinkled into the shadows the brighter the highlights the larger the flash.

Stopping down the lens reduces the preflashing a bit.

I've a set of SC lenses in LTM for canonP and set in silver nose Oly for OM-1, 28, 35, and 50mm.

MC was marketing cunning to get you to upgrade...

 

[Athiril]

The shoulder is further away from exposure since you're exposing lower down on the curve.

If your eg, if your preflash is x, and you compare that to an exposure level only 3 stops higher than x, we'll call that y, then with the preflash x+y = y*1.125, every stop higher the addition is exponentially less.

You may see an increase in shadow detail but it is not due to increased film speed. If you intensify a very thin negative you will see more shadow detail but you have obviously not increased the film's speed. You have just increased the visibility of the detail. Hence the quote from the article in my previous post.

Years ago before the invention of VC paper some photographers would only stock grade 5 paper. Then by pre-flashing they could reproduce any of the lower grades. It saved the expense of stocking many grades and gave the ability to produce fractional paper grades.

It's an increase in actual speed. I do not count detail that doesn't exist on the negative as film speed or shadow detail. The fact of the matter is none of those exposure levels show up in the heavy push without a preflash, it is otherwise a non-developable exposure (cant even find/detect that 'less visible detail' with a high end scan, because it's simply not there), where it is developable, visible, above 0.1d above film base + fog level, and you know, generally actually exists with a preflash, and thus contributes to an increase in film speed.


All contrasts increase and improve, film speed goes up, shadow detail goes up, shadow contrast improves by an incredible margin. Muddiness is removed from the image. Without a preflash you would otherwise need to use a higher speed film to achieve the same sensitivity to light during the image forming exposure.

 

[Xmas]

Hi Arthirl

You are in effect increasing the dynamic range of the film. Rather than just raising the toe speed.
The push will get you more mid and highlight density as well, though reducing the enhanced range a bit.

Your before and afters look real convincing.

A lotta people bought the 40mm and 35mm Cosina M /1.4 lenses in SC rather than MC maybe their cams don't do double exposures?

So the answer to the OP is lots of people are still flashing for speed in mono and speed and reduced saturation in colour.

 

[Rudeofus]

Yes, but the results are rather unpredictable and depend on several factors. This seriously limits what can be done.

This was never presented as simple miracle cure for insufficient light, and Athiril made it very clear that this method requires exposure series and lots of testing. Nevertheless, Athiril's Superia 800 @EI12800 color images are very impressive, and look much nicer than my Portra 400 @EI3200 medium format negatives done without pre- or postflash.

When I did my Portra 400 @EI3200 images, I wanted to include the picture from a TV set in my frame, and extra ambient light wouldn't have helped.

 

[Rudeofus]

You are in effect increasing the dynamic range of the film. Rather than just raising the toe speed.
The push will get you more mid and highlight density as well, though reducing the enhanced range a bit.

A Zone I preflash should have little or no effect on Zone V+ exposures. Remember, zones and exposure values are logarithmic measures.

 

[markbarendt]

Everybody is sort of correct.

Even you.

I even think you taught me this.

Whilst it has been common to illustrate this concept of pre-flashing and flare as changing the shape of the curve, with the flashed toe starting parallel & above the un-flashed toe, the reality is that the curve remains constant. The silver responds appropriately to a given amount of exposure.

The placement of ALL the subject matter simply moves right along the curve with more exposure.

Being logarithmic the subject matter on the left (dark subjects) moves farther across the curve than subjects to the right. The hope with pre flash and flare present is that the subject matter starts climbing the steeper parts of the curve faster than the fog of general exposure behind it.

 

[Stephen Benskin]

Pre-exposure is also subject to low intensity reciprocity failure, so effectiveness is also determined by the time interval between the pre-exposure and principle exposure.