Film speed test in winter

[Stephen Benskin]

In my mind I'm thinking higher intensity causes more reflection off various surfaces (including the emulsion itself), so flare should increase even though the light is present for less time compared with the second exposure. Not sure. And it is difficult to test in practice due to possible shutter speed inaccuracies.

Michael, the higher intensity will of course create a higher reflective light level. But as they are part of the target, which is a uniform luminance source, it has nothing to effect. Think of flare as a bleeding of light from the brighter scene elements (average of 3 percent of the greatest scene luminance) adding to the darker exposure values. If the target is the only luminance value, what is it going to bleed into and how can it add to itself?

Just reading the list of meter modifications (various filters, baffling) was depressing enough

It's enough to make a person question whether knowable testing is possible with such devices.

I'll try to re-read the exposure meter part of Henry's book so the material will be fresh for both of us. One thing to remember is sometimes the variables can create an accumulative effect and sometimes they can cancel each other out. If you have a chance, you might want to check out the thread Is the K-factor Relevant to me or should I Cancel it Out? Around the third page, I begin posting attachments outlining exposure including exposure meters and the variables in the equation for determining K.

 

[Bill Burk]

Really? Even camera flare (light bouncing around in the camera even with flat black surfaces, light reflecting off the emulsion adding to this)?

Right. The light would bounce around just the same, only it would be proportionally dimmer.

Now I use Zones loosely in this discussion. When I test film it's with a sensitometer. Then I work in Zones as I study my graphs because I find it easy to get my head around. I imagine where the different Zones will fall on the curve. I look at Zone I and lift that point to the Y-axis coordinate corresponding to about Zone II (I say about, because I look 0.4 LogE to the right). The difference is a certain number of Meter-Candle-Seconds which I take and "add" to each of the coordinates of my step wedge. Flare's impact quickly tapers off. But this is how I take a sensitometer test and make it agree with light meter marked with Zone System grays.

In a sense I call the camera test you describe as a no-flare test. Even though the camera introduces flare. I say no-flare because the amount of flare at Zone V exposure is about what would take Zone I up to Zone II. BUT, in a camera test you stop down four stops and it no longer brings you from Zone I to Zone II. Now it only takes Zone -III to Zone -II (which is to say 'nada').

 

[Bill Burk]

The whole meter issue really bothers me. ... Just reading the list of meter modifications (various filters, baffling) was depressing enough.

Trust one good meter and leave it at that.

I could wish for a spectrophotometric meter that could be programmed for my favorite film and which also could interpret the effect of black and white contrast filters to predict the Zone System placement. Totally possible with current technology. But that would reduce metering to a "point and shoot" frame of mind, which takes some of the fun (and all the participation) out of it.

Lately, as I experiment with my Weston Master II and Zone System sticker, I once again "walk in the footsteps" of Ansel Adams. I can walk up to a gray wall, set the meter to V. Point at sky and see needle go up to IX. Point at a green plant and stop to think... The Master II selenium cell is making the plant go to VI but I know it is really still V. Finally learning these tricks that used to drive him and Fred Picker to make these modified meters. But they always dealt with it until the Zone VI modified meter came out.

 

[Stephen Benskin]

Ok, in the flare example the more I think about what Stephen said I think we can at least remove reflection off the emulsion. So we've removed that element, and removed the diaphragm as a variable by using and ND filter. So the possibility we're left with is simple camera flare. Here is where I'm still unsure - because assuming I don't mask the lens to an image rectangle with projection limited to the emulsion area, the image circle is larger than the film, so indeed additional extraneous light could bounce off surfaces in the mirror box, onto the film and cause increased exposure. Is this reasoning correct?

I can't speak with any certainty to camera design and all the elements that contribute to flare, but generally what you are describing are things that could add to the level of flare.

If that is correct, the question again would be, given the equivalent image forming units of light in the two exposures (1/60 @ f/2, 1s @ f22), would there be a difference in film density for this relatively low density (actual density or "Zone" not really critical, as long as the net density above FB+f is quite low - say somewhere around 0.1-0.2 above FB+f).

The flare factor is calculated by how much the shadow exposure is affected. I believe the standard practice is to use the shadow exposure 4 1/3 stops down from the meter exposure point of a statistically average scene luminance range. A one stop filter factor means flare doubles the shadow exposure 4 1/3 stops below the metered exposure. If the luminance range is shorter than the statistically average and the shadow exposure doesn't reach down 4 1/3 stops, then there's nothing there to add exposure to. Where the shorter luminance range shadow falls in this example will not experience a doubling of exposure.

Within the same optical system, the only way to change the flare factor is by a change in the luminance range or change in the portion of dark and light tones in the scene and how they are distributed. Adding or reducing the camera exposure should just move back and forth along the x-axis.

Currently reading about K in Henry's book. If I didn't already understand what the K-factor is, I still wouldn't know after reading that section. Another example of how he just might not be into theory. Still have the testing for K to get through.

 

[Stephen Benskin]

I'm not following. Did you mean to say a one stop flare factor? Let's assume the two exposures I listed are both 4 1/3 stops below metered and that the film density under zero flare conditions would arbitrarily be 0.20 above FB+f in either case. In the first exposure, the intensity of light entering the camera is high, and so some of this light (from the portion of the image circle beyond the borders of the emulsion) might bounce around, eventually bouncing onto the film and adding some additional exposure. At least I think it might. Maybe the actual film density ends up being 0.23 above FB+f. In the second exposure, a much lower intensity of light enters the camera, but the shutter is open for longer. Would we still expect a density of 0.23? Or would we actually get the zero flare density of 0.20 because the light intensity is not high enough to cause significant reflections in the camera - even though the film is exposed for longer.

Same scene, same luminance range, and say shot at two different f/stops should have the same flare. And sorry about the "filter factor" typo. It was supposed to be flare factor.

Perhaps there is no definite answer. Here's another way to think about the same example. You take a picture of a bright, uniform, featureless mid day sky and expose it to produce an expected net film D of 0.20. In the evening you take a picture of a middle grey, uniform, featureless evening sky and expose it to produce a net film D of 0.20 (so obviously this would be a significantly longer exposure than the picture of the mid day sky). Assume some camera flare in the first exposure leads to an actual net film D of 0.23. Would that occur in the second example too, even though the intensity of light entering the camera is lower? I'm thinking there would be less, or zero flare in the second exposure. Not sure.

If the featureless sky takes up the entire frame, it's the same as shooting a target. It's virtually a flare free situation, or to put it more accurately, free of the effects of flare.

Keep in mind this question concerns an in-camera film test with as little flare as possible (aside from some degree of lens flare which cannot be totally eliminated). The aim is to use a brightly lit white card for the entire series of exposures. In actuality, the lens is masked to restrict the projected image to within the borders of the emulsion. In other words, there should be no camera flare. But even though I would be using this mask anyway as an extra precaution, I'm wondering if it is necessary. So my example above would be the equivalent of not masking the lens.

You're keeping stray light from entering the camera. The exposure of the white card shouldn't be affected either way. Even with an average luminance range the effects of flare at the point of the white card is inconsequential.

Regarding the K-Factor discussion in Henry's book, as it happens I re-read that very section today, and I came away just as little understanding as when I first read the book. I wish he had started by explaining what the K-Factor actually is before getting into the ranges, calculations, standards etc. I still don't get what the K-Factor is. The only thing I think I understand is that it is not what Adams said it was. When you read Adams you come away thinking it is just a safety factor built into the meter.

With Adams you come away thinking it's a conspiracy. You should read the stuff I wrote n the K-Factor thread. Here's a page.



Henry talks about the various values of K, but he doesn't explain what it is or how it relates to exposure. In Henry's book you come away thinking it's an arbitrary decision by the manufacturer. BTW, he never really defines exposure (or from what I've read so far). I like that he has a bibliography, but he could take the level down a notch and include the titles of the papers. The book isn't for scientific publication.

 

[Bill Burk]

View attachment 63191

Michael R 1974,

Yes Stephen made a tiny typo, he meant Flare factor.

But look at this chart again. Now imagine doing a single-tone film speed test where you meter Zone V and stop down 4 stops (or 4 1/3 stop if you prefer).

When you stop down, you move everything down.

In the middle of the graph, Zone V, the meter point... you see the exposure+flare (realistic exposure) curve practically rejoins the theoretical exposure (45-degree theoretically perfect) curve. So a test exposure is not influenced much by flare.

 

[Stephen Benskin]

I think I'm getting closer to really understanding this.

You've got me doing some thinking.

 

[Chuck_P]

As much as I am a fan of Adams, I think the subject of flare is a real shortcoming of The Negative. It is mentioned in little more than a cursory way, but can be a major source of distortion in Zone System testing and applications. It seems like something that should be given a full explanation even if we can't control it.

Just my thoughts here, nothing critical. My views are geared more toward practicality, which the newcomer or first-timer parusing these threads must never, never, ever lose sight of, in the midst of all this theory.

Your're right, it is not mentioned to any appreciative manner that even remotely resembles the type of discussions that occur here, yet his work speaks for itself, how important was it to him, I don't know, just asking. It begs the question, in my mind, as to just how important it really is in practical film testing for EI and N-times. It makes for discussion, and I do follow it, but just how important is it? This is not to imply that I think it has no affect, only that it's affect, has got to be so dependent on "degree" as to not warrant much consideration in the intellegent use of the Zone System.

From The Negative, Appendix 1, regarding testing (I'm sure you've seen it, but it makes my point): "Choose a film and developer you use often, and be sure to use the same camera, shutter and lens throughout. Your exposure meter, lens diaphragm, shutter, and darkroom thermometer must be reliable----calibrated by a technician if possible. Once this "system" has been tested, any variations introduced by a change of equipment (such as the possible difference in aperture calibration or flare introduced by changing lenses) should be quite apparent if they are significant. For a change in film and/or development, of course, new tests must be conducted."

So, essentially, flare, if significant, should be apparent with intelligent use of the ZS or any system and in that respect I fail to see any distortion in testing or application. I consider myself a competent ZS user and I simply have not been able to make a determination that flare is "apparent" in my "system", even though I'm fully aware that the tests I carry out (an in-camera contacted step tablet, exposed to Zone X to an evenly and diffusely illuminated single tone test target) are flare free. I make a decision before releasing the shutter as to what measure I may take to deal with possible flare influences, it is a negative by negative consideration and I rarely do anything different, and when I do, it is usually a -1/3 to -2/3 reduction in exposure. When compensating for it or not, the desired print is always obtainable as envisioned, flare has not seemed to affect the end result. If I had an older uncoated lens and switched from my new Nikkor to it, well then, it would be "apparent", even before exposure, that flare is going to affect my "placement".

So I disagree with your statement, but given the spirit of the discussion I understand why you make it. In keeping with the OP, I would say to those wishing to carry out film tests for themselves for the first time, to just do it. Find a source i.e., BTZS, The Negative, Schaeffer, Lambrecht----follow it, and it only, to the "T" and be careful of outside advice, it is sure to trip you up. As one understands the concept of "expose for the shadows and develop for the highlights"----which the ZS and BTZS are simple vehicles toward that end, then one already has all they need to know to know how to deal with flare. At that juncture, flare in testing for EI becomes a mute point and you are assured that flare in actual photographing is intelligently dealt with.

Just my opinion folks.

 

[Stephen Benskin]

Originally Posted by Stephen Benskin
Every successful photograph I make shows theory. Isn't that the foundation of your defense of the Zone System? The quality of Ansel Adams' work is proof of the theory.

Originally Posted by CPorter
Putting it in terms of theory is certainly acceptable, but the foundation of my defense of the Zone System lies in learning how valuable (to me) the process of visualization can be. My photographic "craft" is leaps and bounds from what is was, because of the Zone System, and being proficient in the craft of photography is the path to becoming better at visualization, IMHO.

Your're right, it is not mentioned to any appreciative manner that even remotely resembles the type of discussions that occur here, yet his work speaks for itself, how important was it to him, I don't know, just asking.

 

[markbarendt]

Hi CPorter,

I guess all I'm saying is that in The Negative (and many other books, articles etc) flare should be explained, particularly because the recommended film testing methodology does not involve contacting a step tablet. So it again comes back to the interpretation of test results. The effects of non image forming light might be useful to the reader when looking at the curves generated.

Let me ask you this - why a 1/3 to 2/3 stop reduction in exposure when you suspect significant flare effects?

Michael

For one explanation see Dunn & Wakefield Exposure Manual, in edition 3 there is an explanation with graph on page 19.

Essentially flare lifts the toe of the curve more and more as exposure rises reducing effectively contrast on the film. Lower exposure levels when there is significant flare can provide better separation of tones.

 

[David Allen]

"Choose a film and developer you use often, and be sure to use the same camera, shutter and lens throughout. Your exposure meter, lens diaphragm, shutter, and darkroom thermometer must be reliable----calibrated by a technician if possible. Once this "system" has been tested, any variations introduced by a change of equipment (such as the possible difference in aperture calibration or flare introduced by changing lenses) should be quite apparent if they are significant. For a change in film and/or development, of course, new tests must be conducted."

Adams' description here may appear 'wooly' in terms of flare but the key sentences are:

"be sure to use the same camera, shutter and lens throughout" - the reason for this is that the testing procedure automatically compensates for flare.

"any variations introduced by a change of equipment (such as the possible difference in aperture calibration or flare introduced by changing lenses) should be quite apparent if they are significant." - i.e if you have calibrated with one camera, one lens, one meter, one developer, one thermometer, etc introducing a variable such as a different lens will immediately show if flare, for example, is a significant factor. If it is, you then know that you need to re-calibrate for that particular lens by redoing the testing sequence.

Often, particularly with 35mm/roll film users, you will hear comments such as 'my 28mm lens is rather soft compared to my other lenses'. This is actually the photographer describing that a particular lens has more flare (or indeed a different level of coating on the lens) than the others.

A friend of my father - the late photographer James Ravilious - was unhappy with his Leica kit. The reason for this was that he couldn't consistently get the particular results he wanted. James preferred the softer look of older Leitz lenses before the advent of computer re-calculation and multiple coatings on the lenses. His problem was easily solved by getting rid of the newer lenses and buying lenses from the late 1950s. These gave the 'look' that he wanted with consistent tonality. In effect a matched set of lenses that all demonstrated the same level of flare which meant he could do one set of tests and then move on without having to worry.

The lesson here is that, for 35mm and roll film users especially, the goal should be to get a matched set of lenses. In doing so, one can disregard all of the additional theory and get on with the most important aspect of photography - enjoying it!

Best,

David
www.dsallen.de

 

[markbarendt]

David I agree with your Analisys of Adams' method and the observation about how lenses affect the result but a matching set of lenses?

Much of the reason I settle on various lenses is to get various qualities, much more than a focal length change. Mamiya's 150SF is a great example. It can be adjusted to be sharp, f8 or smaller varying amounts of soft can be dialed in as needed with larger apertures, its an exceptional goto lens for portraits and landscape and snaps. This provides for a bit more work when printing but that's ok.

 

[Chuck_P]

Let me ask you this - why a 1/3 to 2/3 stop reduction in exposure when you suspect significant flare effects?

Because flare introduces some amount of unwanted density.

 

[AndreasT]

Who is this Henry you guys are talking about? I couldn't find where he is first mentioned in this long thread.

 

[Stephen Benskin]

"be sure to use the same camera, shutter and lens throughout" - the reason for this is that the testing procedure automatically compensates for flare.

We've discussed this point on a number of occasions. In fact, this was the topic of Michael's question. Long story short. It doesn't compensate for flare. Flare is caused by higher luminances affecting lower illuminances within an optical system. Traditional ZS testing uses a middle gray target of a single tone. Even if flare existed, the influence of flare diminishes as you move up the curve. The metering of the target and stopping down may produce the shadow exposure but it's still the middle tone luminance where even in normal flare conditions, there is little influence. And this is completely separate issue from the question of introducing such a variable into a test.

This is a good example of my earlier topic about the helpfulness of understanding theory. Helpful not so much as part of achieve precision testing. That's not necessary for most photographers. It's helpful in knowing the limitations of the tests.

"any variations introduced by a change of equipment (such as the possible difference in aperture calibration or flare introduced by changing lenses) should be quite apparent if they are significant." - i.e if you have calibrated with one camera, one lens, one meter, one developer, one thermometer, etc introducing a variable such as a different lens will immediately show if flare, for example, is a significant factor. If it is, you then know that you need to re-calibrate for that particular lens by redoing the testing sequence.

This can only be true if the photographer shoots with the same lens at the same f/Stop and shutter speed. And this is a good example of my other point about good testing and bad testing. My contention is that speed testing isn't necessary for most and the only testing really needed is for contrast (and that only applies to maybe 10% of photographers). In order to achieve knowable, quantifiable results, the variables and testing conditions must be known and controlled. In other words, scientific testing. Many of the disagreements about testing come from people arguing from different perspectives. It isn't a question of which is more accurate. But there's a big difference between testing for film speed (scientific) and testing for EI. They are different things and have different purposes.

Sorry, ran out of time.

 

[markbarendt]

I know the effects on the curve. I'm challenging the notion reduced exposure can provide better separations. To me it seems like if anything it would have the opposite effect since it shifts more of the exposure values into the part of the curve where compression is taking place.

Regarding the sources of flare in testing etc, again, I'm refering mostly to flare caused by the subject/test target, not the lens. The kind of "veiling" lens flare Adams refers to is likely a relatively minor issue with most contemporary lenses.

Regarding the separation: My impression is that flare works very much like pre-flashing, the greatest effect is on the lowest values. The more you pre-flash the flatter the toe gets. Less pre-flash/flare exposure as a result of less total exposure means a steeper toe.

As to source, uhhh.

 

[Stephen Benskin]

I know the effects on the curve. I'm challenging the notion reduced exposure can provide better separations. To me it seems like if anything it would have the opposite effect since it shifts more of the exposure values into the part of the curve where compression is taking place.

Agreed.

Regarding the sources of flare in testing etc, again, I'm refering mostly to flare caused by the subject/test target, not the lens. The kind of "veiling" lens flare Adams refers to is likely a relatively minor issue with most contemporary lenses.

About 80% of flare originates with the subject, but it only exists when there's an optical system involved. There are a couple of different types of flare, veiling has to do with the optical system and camera creating an evenly distributed level of exposure. Another type is ghost which produces an image of the aperture.

While flare plays a factor in the determination of film speed, for me it's more about the effect it has on the illuminance range. Kodak's contrast index for normal processing contains a value for flare. Their numbers won't work without it.

 

[kbrede]

Who is this Henry you guys are talking about? I couldn't find where he is first mentioned in this long thread.

My guess is it's this guy Andreas:

http://www.amazon.com/Controls-Blac...459&sr=1-1&keywords=richard+henry+photography

 

[markbarendt]

I don't think that under exposing is being suggested, minimizing might be a better description, or maybe giving up the safety factors.

Flare, like flashing, essential raises the lowest values significantly, easily doubling the density, without moving the highest values much at all, maybe 1%ish, you knew that though I'd bet.

Flare, I theorize, like flashing needs to surpass a threshold point to have a significant effect. Less general exposure can help keep flare/flash exposure under the required threshold and therefore affect the image less.

 

[Stephen Benskin]

the most important takeaway is that just because a well respected photographer says something about exposure, development, contrast, chemicals etc doesn't mean we should simply accept it as fact, especially in cases where no evidence, or a proper description of the experiment is given. And the description of the experimental method is very important. Even when presented with data (a characteristic curve for example), if we don't know how the test was done, it is often difficult to conclude anything.

Well put!

One of the reasons why using the prefixes CI and ISO means the testing adhered to a methodology.

 

[Bill Burk]

I don't think it works that way with subject flare, where the high lumincances affect the lower ones. I think the characteristic curve under those conditions is basically a "given" (ie we cannot control the flare), and increasing or reducing exposure simply moves the subject range up and down that curve. So reducing the exposure would result in more compression because more of the subject values fall on the flattened portion of the curve.

Keep in mind that flare doesn't change the film's toe... it only affects the light falling on the film plane.

This is an example situation where you can see "more clearly" what's happening because you separated your flare tests from your film tests.

So the flare light provides enough light to lift you off the toe. There is compression, but it's compression of the light bringing you shadow tones to the film. Nothing you can do about that (except maybe a compendium hood) but try to keep the lowest of the shadow tones on the straight line portion of the film.

But since flare lifted you up off the toe, you can still reduce your exposure and remain above the toe.

 

[AndreasT]

You guys are running away leaving me behind.
What I gather rather expose more to reduce flair instead of decreasing exposure. Which I think is better anyway if the light permits.
Otherwise if one decreases exposure one should extend development by an "X" amount to have a general compensation for the resulting flatness.
You do some disagree?

 

[Stephen Benskin]

Keep in mind that flare doesn't change the film's toe... it only affects the light falling on the film plane.

This is an example situation where you can see "more clearly" what's happening because you separated your flare tests from your film tests.

Bill, I've been wanting to touch on this and even thought about doing it in a new thread. I need to put together a couple of illustrations.

In the mean time, here is a chart showing the values off of my four quadrant curves. The top set of numbers are from a no flare situation. The bottom from a one stop flare. Both exposures place the Zone I exposure on 0.10 over Fb+f. Flare has doubled the shadow exposure from 0.0041 to 0.0082. The value of 0.0041 is added to each step. At Zone VIII, it doesn't even make a dent. Flare has also reduced the 8 Zone range down to 7. The 1.14 non flare NDR becomes 0.98 with flare. The paper grades are adjusted to match the NDRs and LERs. The Q4 reproduction curve gradients show how the local contrast is affected.

 

[Chuck_P]

I don't think it works that way with subject flare, where the high lumincances affect the lower ones. I think the characteristic curve under those conditions is basically a "given" (ie we cannot control the flare), and increasing or reducing exposure simply moves the subject range up and down that curve. So reducing the exposure would result in more compression because more of the subject values fall on the flattened portion of the curve.

It's already been established that flare is "high luminances affecting low luminances" and that there are two types "veiling" and "ghost" (or polygonal flare)-----and, that it does not exist unless there is a lens to deliver it to the film. The flare that I may try to counteract is certainly not "ghost" flare, but the veiling kind that is going to raise density in the low zones where I don't want it. This is not unlike pre-exposure to the film that does the same thing, add density to the low zones, but with pre-exposure, it is purposeful and desired. So, reducing exposure, will reduce exposure to all subject luminances equally, I could not use the term "compression" to describe the result of reducing exposure. Too much reduction, obviously, can push important negative detail clean off the curve, but I fail to see, at the moment, where any compression of values occurs at all.

 

[markbarendt]

So, am I wrong in thinking that flare is a generalized, like pre-flashing.