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

Michael R 1974 said:

Part of me prefers the way you say it, because it clearly separates the flare effect from engineered emulsion characteristics. The other part of me prefers showing flare (or pre-exposure) as an overlay to the sensitometrically exposed curve, just because I think that's how most people, ZS users etc. might better understand it. Not sure. Just my two cents.

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You are correct in both appreciations but I'm a ZS person.
I regard the non linearity at toe as a problem and would want to compare two films with an optimal preflash or I'd want to see how they behaved with a pre-flash.
Tx, HP5+, 5222, etc. & neopan400
Ie I regard the flashed film as a custom reengineered film...
Most of my shots are with a single coated lens eg a Canon lens made in '62 it is the photo engineer...
Not many manufacturers publish even abstract H&Ds, eg like foma's
Most seem to want to tell me how to process film in general which I can better get from a book if I did not know.
Kodaks instructions even include techniques for slow balls or googlies depending on your sport.
The data sheet is full of marketing by product of the cow.

Rudeofus said:

Jerry, as you sure know, density is a logarithmic measure of absorption. My statement stands as I wrote it. No densitometer I am aware of can measure density without forming the logarithm of measured light.



Many people associate the term "linear" with straight line curves, but I thought about something else: L(a*X + b*Y) = a*L(X) + b*L(Y). Such a relationship will obviously not hold across the whole characteristic curve, but in most sections it will hold in infinitesimal regions where a linear interpolation is possible. In the lower toe region, though, we have this "three silver atom" threshold, and that relationship above will not hold even locally. This is where the characteristic curve falls apart, this is where Mark's theory "it doesn't matter how many exposures contribute to the total amount of light" falls apart, and this is likely where Athiril got his extra stops of real sensitivity from.

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Thanks Rudy, interesting stuff.

Michael R 1974 said:

The other part of me prefers showing flare (or pre-exposure) as an overlay to the sensitometrically exposed curve, just because I think that's how most people, ZS users etc. might better understand it. Not sure. Just my two cents.

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I learned the concept that way. Studying Adams etcetera. It got me to a point where I could use the technique.

Visualizing it on the H&D curve worked fine as long as I didn't try to use the scales at the edge of the chart.

I was at a workshop in Tonopah years ago with Per Volquartz, when he demonstrated the technique using Type 55 (insert tears here, one for Per and one for Type 55) The difference in the control print and the demonstration print were startling. Both looked nice. It was a clear demonstration of a master being able to manipulate results beyond the simple one off triad terms most people use to describe exposure.

For me is an effective tool for certain situations. If it works and how well it works is a matter for the practitioners taste and ability. In regard to the OP, that some photographers find it a useful technique is undeniable. Arguments beyond that are subjective.

Interesting,I had that conversation with Per in Tonopah too.

Athiril said:

vs Zone III (12800) preflash

Superia 800 @ 12800 Zone 3 preflash by athiril, on Flickr



Going back to that example, it doesn't appear as expected behaviour if


Zone 1 = 1
Zone 2 = 2
Zone 3 = 4
Zone 4 = 8
Zone 5 = 16
Zone 6 = 32
Zone 7 = 64
Zone 8 = 128
Zone 9 = 512
Zone 10 = 1024

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Assuming colour print film with normal development gives 7 stops of useable range and assuming you exposed at 12800 then your main exposure would give following because you have underexposed by 4 stops.

Zone 1 = 0
Zone 2 = 0
Zone 3 = 0
Zone 4 = 0
Zone 5 = 1
Zone 6 = 2
Zone 7 = 4
Zone 8 = 8
Zone 9 = 16
Zone 10 = 32
Zone 11 = 64

then you pre-flash. Question is at what EI? 800 or 12800? I don't know cos you don't say.

Assuming it was 800 then you get following (if was at 12800 then it wouldn't register).

Zone 1 = 4
Zone 2 = 4
Zone 3 = 4
Zone 4 = 4
Zone 5 = 5
Zone 6 = 6
Zone 7 = 8
Zone 8 = 12
Zone 9 = 20
Zone 10 = 36
Zone 11 = 68

Then you push development by 4 stops and that gives? I have no idea because I never tried or measured it but it will certainly increase separation between zones steepening the contrast curve. And since we are looking for a 7 stop range we are looking to push the zone 7 value up to around 64 which I guess a 4 development stop push would, possibly even to 128.

This would give something like:

Zone 1 = 68
Zone 2 = 68
Zone 3 = 68
Zone 4 = 68
Zone 5 = 69
Zone 6 = 70
Zone 7 = 72
Zone 8 = 56
Zone 9 = 84
Zone 10 = 100
Zone 11 = 132

This is why me and others are saying a pre-flash can produce muddy shadows (look at the zone 1 to 4 values). Your results don't show that which may mean you pre-flashed at 12800 and/or you are using the 7 stop range from zone 4 to 11 to print your result from the negative.

There's an awful lot of me guessing this is what happened in your result. Too many unknown varaibles(to me) to provide anything precise.

Michael R 1974 said:

They should say - "this is how I do it:..." and stop there, rather than going on to explain what is happening (what they think is happening) and how it works (how they think it works).

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That is a great goal and a skill I'm working on.

I do though see these threads as conversations in an open classroom, more than as textbooks.

In black and white work, if you want something with a more gradual toe, it's just so damn much easier to pick a film with that characteristic to begin with. Flashing in the field is just a band-aid. Pre-flashing in the lab can be done with a bit more precision usually, unless you've made a really nice flashing diffuser for the lens position in front of the lens and carefully measured it in advance. The nice thing about these if they're based on a gel holder is that you can all insert color-correcting gels for minor correction in color film shadows. If you've go a color temp meter around and good color test chart you can experiment in advance and really fine-tune this kind of accessory.
With color film you can really screw things up fast if you over-flash. I really don't like the effect if you go above Zone III in color neg work
(mixing Zone lingo with color film isn't something I like to do at all, but it's easy to relate to in this context). With black and white it all depends on the specific film, since some will separate shadows way down there. But crisp shadow separation is something you sacrifice with flashing. If it is all there on the neg, unsharp masking is a much better tool for opening up shadows without sacrificing tonality; but that is a bit more involved to do well. Simply using compensating development or "minus" development reduces overall contrast but also
gives up a lot. If you've being constantly haunted with these kinds of problems, maybe time to look at a different film to begin with.

Michael R 1974 said:

The answer is few photographers, regardless of whether or not they are "masters", should be writing as authoritatively as they do about topics in sensitometry and tone reproduction. They should say - "this is how I do it:..." and stop there, rather than going on to explain what is happening (what they think is happening) and how it works (how they think it works).

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I agree completely. With respect to Michael's post I think of Harry Champlin who was a phorographer who also wrote a book "Champlin On Fine Grain." The book describes his attempts to formulate a fine grain developer. Since he knew absolutely nothing about chemistry the book is very amusing.

DREW WILEY said:

In black and white work, if you want something with a more gradual toe, it's just so damn much easier to pick a film with that characteristic to begin with.

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If you start with the lowest contrast toe e.g. HP5+ or Tx or may be Delta3200 and you want to up the ISO without losing shadows what do you do? Note alas Tmax3200 is history.

Michael R 1974 said:

It can be useful to know what it is doing, otherwise arguments for or against amount mostly to noise.

What I like about this thread is it potentially makes the subject of flare more concrete to the average ZS practitioner. Pre-exposure, flashing, any use of non-image forming light is controlled flare. Since there is almost always some amount of flare when we photograph, there is always some amount of pre-exposure.
<snip.>
The answer is few photographers, regardless of whether or not they are "masters", should be writing as authoritatively as they do about topics in sensitometry and tone reproduction. They should say - "this is how I do it:..." and stop there, rather than going on to explain what is happening (what they think is happening) and how it works (how they think it works).

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Maybe - all I do is use a single coated lens when I don't have total overcast.

A single coated (SC) lens reduces high lights spilling them into shadows flashing (and maybe as well fogging) the shadows, the amount varies on a really bright day I get more reduction and more fog... I use a deep hood to avoid iris images and the like.

When I have time I meter for zone 1, still burn highlights lots of time.

All I can say is a large number of people do this, e.g. Cosina Voightlander did a reasonable % of their 35mm and 40 mm f1.5 M lenses in SC rather than multi coated (MC), they got more SC customers than they initially expected.

As well as controlling the dynamic range the SC lens gives more bleed over, artifice on light sources, etc. so the shot looks like a real photo.

It is rare I use colour but the SC lenses do also mute saturation pastelling colours, the degree again depending on brightness range.

If I used a MC lens Id have blacker shadows and brighter highlights which I don't need on sunny days.

Some 'D' camera people do the same.

I used to preflash graded paper and slide duping film for contrast reduction long time ago...

RobC said:

This is why me and others are saying a pre-flash can produce muddy shadows (look at the zone 1 to 4 values). Your results don't show that which may mean you pre-flashed at 12800 and/or you are using the 7 stop range from zone 4 to 11 to print your result from the negative.

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Let's not argue his results with the zone system. Your whole set of calculations assumes that Athiril printed his negative optically, but I remember him writing elsewhere that a very hybrid process followed the development of these negs before he obtained those images. This doesn't take much away from Athiril's accomplishment, after all he could extract image detail where a neg without preflash had none.

Michael R 1974 said:

I didn't mean you or anyone in this thread. I meant guys like Barnbaum, Thornton etc. who write books with entire chapters of, well, not very good information. And the most irritating part of that with Barnbaum is he goes out of his way at the outset to belittle sensitometry/densitometry, and seems especially proud to proclaim he has never owned a densitometer. I'd be fine with that if he simply stopped there. I'd be the first to say you don't need a densitometer, exposure theory etc. to become an excellent printer. The problem is he then proceeds to draw curves, talk about how compensating development works, why Ansel is wrong about pre-exposure, why Zone III is no good, why there is no such thing as dry-down, and on and on.

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I knew you weren't picking on me.

I think what you describe is the norm in much of the "self help/how-to" genre of any subject. It's as if the authors know they need 300 pages to be considered credible but their idea only takes 100 pages to explain.

Rudeofus said:

Let's not argue his results with the zone system.

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I'm not arguing his results. I'm just making the point, if you had read it all and understood it, that we have no way of knowing exactly how/why his results are as they are.

I think anyone having read this topic and understood it should by now understand that pre-flash needs experimenation to get it to work for you and in some cases it will work quite well and in others maybe not so well. It isn't a magic bullet.

"Pushing" (a completely wrong term in black and white processing to begin with) will do next to nothing to improve shadow gradation. With
overdevelopment you primarily increase contrast toward the top of the film curve and somewhat down into the midtones, not at the toe.

Pushing makes all the difference in the world. I've done this test through regular development times without a push at various exposure and pre-flash levels, the difference is minimal and not worth pursuing, essentially not pushing makes the technique for increased speed useless.

Not to mention that without pushing, your scene dMax is 4 stops of exposure lower in the same scene, everything is simply lower.

RobC said:

Assuming colour print film with normal development gives 7 stops of useable range and assuming you exposed at 12800 then your main exposure would give following because you have underexposed by 4 stops.

Zone 1 = 0
Zone 2 = 0
Zone 3 = 0
Zone 4 = 0
Zone 5 = 1
Zone 6 = 2
Zone 7 = 4
Zone 8 = 8
Zone 9 = 16
Zone 10 = 32
Zone 11 = 64

then you pre-flash. Question is at what EI? 800 or 12800? I don't know cos you don't say.

Assuming it was 800 then you get following (if was at 12800 then it wouldn't register).

Zone 1 = 4
Zone 2 = 4
Zone 3 = 4
Zone 4 = 4
Zone 5 = 5
Zone 6 = 6
Zone 7 = 8
Zone 8 = 12
Zone 9 = 20
Zone 10 = 36
Zone 11 = 68

Then you push development by 4 stops and that gives? I have no idea because I never tried or measured it but it will certainly increase separation between zones steepening the contrast curve. And since we are looking for a 7 stop range we are looking to push the zone 7 value up to around 64 which I guess a 4 development stop push would, possibly even to 128.

This would give something like:

Zone 1 = 68
Zone 2 = 68
Zone 3 = 68
Zone 4 = 68
Zone 5 = 69
Zone 6 = 70
Zone 7 = 72
Zone 8 = 56
Zone 9 = 84
Zone 10 = 100
Zone 11 = 132

This is why me and others are saying a pre-flash can produce muddy shadows (look at the zone 1 to 4 values). Your results don't show that which may mean you pre-flashed at 12800 and/or you are using the 7 stop range from zone 4 to 11 to print your result from the negative.

There's an awful lot of me guessing this is what happened in your result. Too many unknown varaibles(to me) to provide anything precise.

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When I say Zone = x and give a scale like the one I give, it refers to exposure, and not what is on the negative, starting at 1 is arbitrary, it just can't be 0 because it will never be 0.

Your scale is wrong for what is on the negative that will be measured in optical density, and it will be 0.3d per stop, and not double for every stop, and every stop of exposure isn't going to be 0.3d increments on the neg.

I've mentioned a few times, the Zone III preflash refers to a speed of 12800, or Zone -1 for box speed if you will.

Rudeofus said:

Let's not argue his results with the zone system. Your whole set of calculations assumes that Athiril printed his negative optically, but I remember him writing elsewhere that a very hybrid process followed the development of these negs before he obtained those images. This doesn't take much away from Athiril's accomplishment, after all he could extract image detail where a neg without preflash had none.

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I think 'did you print this optically?' is kind of silly, the ratio of people who use colour film to the ratio of people who also optically print it is much wider than the people who are into photography vs the people who also use colour film to start with.

Regardless the results were scanned on a Fujifilm SP3000, it is essentially 'fixed grade', it is very much like printing and offers density (exposure) and colour balance adjustments just like enlarging does, it does not let you set a black and white point.

The 12800, 3200, and 12800 + preflash samples were scanned the same without density adjustments even iirc, no contrast adjustment etc. Meaning the 12800 + preflash is very similar to the 3200 image, maybe even a little higher in the highlight values, not lower as you would expect.

I also checked it out on a Flextight scan and could not pull any of the missing shadow detail out of the non-preflash shots at all in Photoshop, meaning if I couldn't do that, you certainly would never find it by optically printing it.





My test is the only actual data/evidence/samples I've seen of pre-flashing negatives in my life, anything else I've seen about pre-flashing is just claims and information that is borrowed from someone else's claims and parroted.

That said it should work fine on B&W, after all I had based it on the incredible claims of another author online about pre-flash and pushing Tri-X to very high speed and obtaining detail otherwise not possible, to which I found true on this particular film on my very first test.

His method was to bracket pre-flash a roll only (no image exposure) and develop it at a push time and see the frame that has any density at all is the one to go with, and then use that on the next rol. Mine was to bracket pre-flash along with image exposures and judge it directly on the best looking image, as I thought it still could occur prior to any density increase from pre-flash only pushing up exposure values, or even after with a thicker fog.

I'm sure DPUG is the palce for this.

DPUG is not the place for pre-flashing. DPUG is also probably the last photo forum I'd recommend to anyone ever.

DREW WILEY said:

"Pushing" (a completely wrong term in black and white processing to begin with) will do next to nothing to improve shadow gradation. With overdevelopment you primarily increase contrast toward the top of the film curve and somewhat down into the midtones, not at the toe.

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I don't disagree with you one bit Drew. I visualize adjustments to development like a door swinging with the hinge at the toe and the straight line as the door.

In fact though your post got me thinking that the problem you point out here is actually a good reason (at least for me) for not using an overlay.

Since Pre-flash and flare push the subjects further right, on the engineered curve, that also means that those tones are farther from the hinge point and will "swing" more with extra development.

An overlay might hide this effect, possibly leaving one to wonder why it worked better than expected.

This is the article that got me to try this in the first place
http://strobist.blogspot.com.au/2013/02/how-we-got-here-analog-photoshop.html

markbarendt said:

I don't disagree with you one bit Drew. I visualize adjustments to development like a door swinging with the hinge at the toe and the straight line as the door.

Since Pre-flash and flare push the subjects further right, on the engineered curve, that also means that those tones are farther from the hinge point and will "swing" more with extra development.

.

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Two points

a) when you develop for longer or hotter the HD curve does rotate anti clockwise but the base fog lifts as well so you can lose toe speed...
See the Fomapan site for their data sheets

b) preflash flare and image light are each photons but if you do a eg ISO test without two of them it does not characterise the film for the combination of the three.

So if you do an ISO test 1/125 with a contact step wedge and an ISO test with preflash and step wedge in enlarger you will get rather different results.

An ISO test is done with a standard developer etc. it is not an engineering test for anything else when you do anything different e.g. Employ a 5 minute exposure you need to redo the test for 5 minutes

I've spent a whole weekend preflashing with a box of graded paper and a step wedge and a high key negative the box went in the bin I had not been able to control the fog level I'd a needed to dab Farmers reducer on prewetted print.

Noel,

A) The film isn't really losing toe speed, the film's toe just gets buried in the fog age or exposure or... You could think of a film's curve a bit like a road leading up a hill out of a valley, the road is there, whether there is fog in the valley or not; the fog doesn't change the path of the road.

B) Yes you need to do the math to correct for reciprocity failure etcetera to make my thoughts work.

Xmas said:

An ISO test is done with a standard developer etc. it is not an engineering test for anything else when you do anything different.

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The ISO standard for b&w film speed hasn't used a standard developer since before 1993. I agree, it is only about determining film speed. That's why other tools exist such as the tone reproduction diagram. Now there's nothing wrong with combining multiple variables into a single curve, but there are down sides.

RobC's three silver atoms is known as the Gurney-Mott Hypothesis of Latent Image Formation. What many people don't know is that low intensity reciprocity failure is factored into the ISO standard as hold time. The 1993 standard defines it as "The processing shall be completed in not less than 5 days and not more than 10 days after exposure for general purpose films, and not less than 4 hours and not more than 7 days after exposure for professional films." Reciprocity failure is part of the ISO standard and should be considered whenever doing any test. It's just another variable. Considering this, I don't see how the characteristic curve falls apart.

markbarendt said:

Noel,

A) The film isn't really losing toe speed, the film's toe just gets buried in the fog age or exposure or... You could think of a film's curve a bit like a road leading up a hill out of a valley, the road is there, whether there is fog in the valley or not; the fog doesn't change the path of the road.

B) Yes you need to do the math to correct for reciprocity failure etcetera to make my thoughts work.

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ISO speed includes a detectable density above fog criteria so if the fog goes up faster than the toe for whatever reason the ISO goes down?

and your EI would need to go down as well always assuming you are wanting to use zone 0 and 1

Id say you need to do the step wedge for reciprocity then work out the factor for the ISO from the HD...

Ditto preflashed film (or paper).

Stephen Benskin said:

The ISO standard for b&w film speed hasn't used a standard developer since before 1993. I agree, it is only about determining film speed. That's why other tools exist such as the tone reproduction diagram. Now there's nothing wrong with combining multiple variables into a single curve, but there are down sides.

RobC's three silver atoms is known as the Gurney-Mott Hypothesis of Latent Image Formation. What many people don't know is that low intensity reciprocity failure is factored into the ISO standard as hold time. The 1993 standard defines it as "The processing shall be completed in not less than 5 days and not more than 10 days after exposure for general purpose films, and not less than 4 hours and not more than 7 days after exposure for professional films." Reciprocity failure is part of the ISO standard and should be considered whenever doing any test. It's just another variable. Considering this, I don't see how the characteristic curve falls apart.

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Besides ISO 6:1993 (Black-and-white), this thread might find insightful the ISO 2240:2003 (Colour reversal) & ISO 5800:1987 (Colour negative)

Determining speed for B&W is similar to colour negative film but the later involves blue, green, red curves.
For color reversal film the ISO speed is determined from the middle rather than the threshold of the curve;

ISO 18928:2013 might be of value for critical test as well.