BTZS and low contrast scenes

[Jorge]

Oh yeah, and before I forget...first thread on the "ignore thread list".....

 

[Kirk Keyes]

Joe - I have read it with an open mind. And Joe, If you find this B-O-R-I-N-G, then why reply? Anyway, I have paid my taxes, thanks for the reminder though.

You cannot properly draw the conclusion that CI is not dependent on exposure just because your premise that gamma, CI, spectral properties, camera exposure, etc., are not the same thing. Doesn't follow.

Please explain how these factors are the same thing - subject luminance ratio; camera exposure level; color of light; gamma? They are not. They are independant variables. I can pretty much set each one of them to nearly any value I wish. They are not dependant on each other.

Todd and Zakia said: “ In roll film, we may develop all the frames uniformly to a gamma of 0.75, but the negatives will no doubt have different total contrasts because of the variations in subject matter at least"

implies a subject with an inherent exposure variation ("variations in subject matter") instead of a single exposure value (as in a blank frame)..

They refer to the subject luminance range here and they are making a general case. I am using a specific case in this thread where the subject luminance range is zero.

So let's use BTZS-type terms here: You surely agree that they are discussing SBRs at 7, right? How about 6, or 5, or 4? Still lots of variation there in the "inherent exposure variation" as you put it.

Here's a question - at what subject luminance range or SBR did that film, which they said was developed uniformly to a gamma of 0.75, loose the gamma of 0.75? They said that the entire roll was at 0.75. Is it at SBR 3, or 2, or 1, or 0.1, or 0.001? When did the gamma drop to zero? Where?

At no point do they mention that what the level of the subject luminance range was, or even what the actual expsoure was. That is because they understand that gamma or CI is, in addition to a measure of a film curves gradient, it is also a measure of development. Not exposure, not subject luminance range.

If you reread what they are saying with an open mind, you will discover they are in fact discussing more than a single point whenever they discuss exposure in relation to CI or gamma.

They are not discussing exposure range here. They are discussing development.

Did you ever consider that Todd and Zakia may have made an error of omission by not simply stating that CI (or gamma) was dependent on 2 (or actually 3 in the case of CI) data points? I would bet that they thought the concept of a measurement of slope (a contrast) was so straightforwardly dependent on two or more data points that they just never mentioned it. Nothing you have said above changes that fact.

Sure, I can consider it. But they had already clearly discussed the mathematical technique needed to calculate gamma or CI earlier in the book, and they appearantly felt they did not need to repeat it. It is straight forward, as you say.

Did you ever consider that they are discussing an index for the measure of development, as they say they are discussing?

You've not given any example by any of these sensitometrists where a variation/difference/contrast in exposure isn't implied in their discussion of developing a film "TO" a certain CI rather than "FOR" a certain CI. You are just choosing to overlook the implication that, for example, a portrait has many different exposures which have been taken simultaneously and from which one can develop TO a certain CI as well as FOR a certain CI and derive the measure. Nowhere have you *proven* a blank frame can be developed TO a certain CI.

I see you included the words "and derive the measure {of the CI}." I think you will find I have never argued that you can calculate there actual CI of a sheet of film if it is blank. I have repeated this several times. Please note that. I agree that you can not.

But it is a different thing to process a film to a desired level. Just because you can't prove it directly from that piece of film, because it did not contain the necessary levels of exposure needed to generate sufficient data points to directly calculate it, does not mean it did not recieve the desired level of development, the desired CI or gamma.

You may be able to measure it indirectly, say if you processed a control strip along side your roll. Or you may need to infer it from the information that you have gained through process control - you ran a control strip 15 minutes before and it achieved your desired level of CI and you ran one 15 minutes after your roll of film and it also achieved your desired level of CI. You can be pretty safe in inferring that your roll of film also recieved that level of processing. Regardless of the exposure that the film recieved.

It's not a trivial, nit-picking point, as some have made it out. It is a basic concept of film processing that I would have thought would be more appearant given some thought. (I do agree it may not be immediately appearant though.)

And as far as not quoting any of these sensitometerist giving a quote "where a variation/difference/contrast in exposure isn't implied", I did. How about

Tood and Zakia, "Gamma is a useful measure of the degree or extent of development."

They say nothing about variation/difference/contrast in exposure there.

How about from "View Camera Technique", 6th ed. by Leslie Stroebel. "Gamma is defined as the slope of the straight line of the characteristic curve, and it is useful because it is a simple objective concept that takes into account the various factors that determine the degree of development - developer activity, time, temperature, and agitation - for a given emulsion."

Stroebel does not mention anything about variation/difference/contrast in exposure. He does not even mention exposure! Only factors of development.

And please consider this - From "The Theory of the Photographic Process", 3rd Ed. by C.E.K. Mees and T.H. James, "Any value of fog given for a photographic material must obviously be accompianied by some specification of the development time or the degree of development (in terms of gamma) for it to have any definite significance".

Perhaps that quote clears it up. Mees and James recognize that a piece of film with no exposure has a gamma (and therfore a CI). Do they say there must be a range of densities - no. Do they discuss the variation/difference/contrast in exposure - no.

So what do Mees and James understand that seems to not be appearant to some of the participants in the thread? They understand that blank, unexposed film has the property of gamma, and that the gamma is dependant on the degree of development. Not exposure.

Kirk

 

[Kirk Keyes]

Since your blank film has no curve and it has no two points, you have no CI in a blank piece of film as quoted by your sources.

You just can't calculate it directly from that sheet of film. See the previous post.

 

[Jorge]

You just can't calculate it directly from that sheet of film. See the previous post.

LOL...well if you cant measure it, then you dont have it......

Look, if it makes you feel good to have the last word, I hope you realize that you are not "winning" any discussions by the power of your reasoning, but by attrition. People are gettring tired of reading your 2 page long foolishness in an effort to prove a stupid point anybody can see you are wrong.

What you are displaying here is not a command of the subject, but a childish stubburness to be always right and "show" the rest of us. Let me assure you, you are becoming the laughing stock of this site very fast judging by the amount of PMs I have been getting about you. As Donald wrote, your notoriety is not one of admiration but one of "there goes this a**hole again."

I know that as far as I am concerned my opinion of you has radically changed, and from the messages I have gotten you jdef and Beskin are very quickly being lumped with the likes of scarpitti/ornello. If you want people to respect your point of views, you should learn to give it a rest once the thread has grown to 11 pages of endless repetition.

In the end , I have yet to see you "win" a discussion, what I have seen is you drown people with endless meaningless facts that it becomes too tedious and boring.

Dont bother on replying, I have placed this thread in the ignore section....I am just giving you a friendly advice in return for the help you provided to me in the past. As far as I am concerned we are even....I wish you luck and hope you heed my advice.

 

[Kirk Keyes]

Do you actually read the posts? If not, please block them.

 

[Ole]

Kirk, the concept of slope in a point is as difficult to understand for some people today as it was for the philosopher Zeno. The concept is still fundamental, so Achilles will still outrun the tortoise - regardless of what some people insist on believing.

 

[Jorge]

Poor Jorge; everything is a contest, and he just can't win. For my part, I'm very flattered to be mentioned in the same context as Kirk and Stephen, both of whom I admire very much. As for Donald, well, the company one keeps .....

Jay

You know Jay, I dont know if everything is a contest, but I least I am not afraid of showing the product of my expertise......something you clearly are. As to being named along Kirk and Stephen, dont flatter yourself too much, I will admit they know what they are talking about....that is not the case with you...

 

[Claire Senft]

My one thought. SBR as defined by Davis is a measurement of shadowed and lit areas of the scene. To this difference is added 5...so that a difference of 1 stop would yield an SBR of 5+1 or 6. I can also see that a planar surface that is evenly lit would be 0+5 =5. So, If one is using SBR as defined by Davis how do you mange to get an SBR <5? other than extreme flare.

I have no problem with the idea that reflected readings will produce differences of less than 5 stops.

David Kachel in writing in Photo Techniques magazine recommended the use of Koadak Professional Copy Film for large expansions. It is a double coated emulsion. Exploiting these differences allows substantial expansion to take place.

Adam's conjectured that Technical Pan film, now discontinued, might be of some usage since one can produce extreme contrast with the film.

I am nowheres near up-to-date on Ortho sheet films but I would imagine that there are several which are slow, fine grained and quite capable of pluss development....the problem may well be to have little enough contrast so that you have no created far more expansion than is desired.

 

[Stephen Benskin]

David Kachel in writing in Photo Techniques magazine recommended the use of Koadak Professional Copy Film for large expansions. It is a double coated emulsion. Exploiting these differences allows substantial expansion to take place.

Adam's conjectured that Technical Pan film, now discontinued, might be of some usage since one can produce extreme contrast with the film.

I am nowheres near up-to-date on Ortho sheet films but I would imagine that there are several which are slow, fine grained and quite capable of pluss development....the problem may well be to have little enough contrast so that you have no created far more expansion than is desired.

Claire,
Jay has started a new thread that takes this subject in a slightly different direction. It promises to be very interesting. You should check it out and maybe even repost this message there.

 

[Kirk Keyes]

So, If one is using SBR as defined by Davis how do you mange to get an SBR <5? other than extreme flare.

Claire - That was one of the questions I had when I started this thread. Determining development times for situations that would be associated with SBRs less than 5 is easy. Just do the testing and you will probably find a point that lies in that range, if you use short enough development times.

So the big question I had was how could you actually measure the lighting conditions if they did fall in that range. By my understanding of Davis's definition, you should not have these situations as you pointed out; 5-0=5.

But if you check on pages 3, 4, and 5 of this thread, Sandy King did address metering techniques that could be employed for scenes that may need this level of expansion. He says it works.

Kirk

 

[Claire Senft]

One of course may use terminolgy as they wish. I am very much under the impression that Mr. Phillip Davis id the originator of this term Obviously. I may be incorrect as i so often am. However, If I am not than I do NOT believe an SBR of <5 exists as staed above.

I am not that most percetive reader but I saw nothing written by Mr. King that changes my opinion...and I am a photographer who highly values and greatly appreciates Mr. King's opinion.

 

[Kirk Keyes]

However, If I am not than I do NOT believe an SBR of <5 exists as staed above.

I am not that most percetive reader but I saw nothing written by Mr. King that changes my opinion...and I am a photographer who highly values and greatly appreciates Mr. King's opinion.

I value Sandy's opinions too.

But I agree with you about the less than 5 SBR idea. The solutions offered do seem kind of kludgy, as I said earlier. I need to play with it and see what happens in the real world.

 

[Jorge]

I value Sandy's opinions too.

But I agree with you about the less than 5 SBR idea. The solutions offered do seem kind of kludgy, as I said earlier. I need to play with it and see what happens in the real world.

I too was confused by this and asked Phil about two years ago. Here is his response:

Jorge --

You obviously can't measure a 4-stop SBR directly but it's certainly possible to assign a range of less than 5 to your subject if you want to treat it to much higher than normal development. The "5 stop minimum" is based on the incident meter dome's 18% transmittance which is equivalent to 2-1/2 stops less than 100%, and (when doubled), perhaps coincidentally, closely matches the typical reflectance range of flat copy, such as a magazine page with "black" ink on "white" paper. In other words, reflectance readings of those extremes of tone are usually in the vicinity of 1.5 which is equivalent to 5 stops.

It's reasonable, therefore, to assume that any 2-dimensional, uniformly illuminated subject — (and this is important) that you wish to reproduce with realistic contrast — can be considered to be a 5-subject, regardless of its apparent tonal range. If its a normal full-scale subject, it'll be reproduced that way in the print; if it's a low-contrast subject (gray on gray) that's how the print image will also look.

But that may not be how you'd like to interpret it. For example, you might want to photograph a petroglyph of brown pigment on gray rock of similar value. Using a 5-stop (or greater) range will produce a very low contrast image so you might arbitrarily treat it as a 4-stop subject which will greatly increase development time and therefore increase image contrast significantly.

The ExpoDev Palm program is set up to make this possible with the Incident metering method (not the ZS). You can take a single "low" reading to establish the exposure then arbitrarily enter a "high" reading that's as much as 2 stops less (corresponding to an SBR of 3 stops). This is very strong medicine and it's very likely that common materials won't be able to produce that degree of contrast, but if you have a film/dev combination that will permit it, you can enhance image contrast dramatically.

Incidentally, you can check your materials to see if they're capable of working in that contrast range by dividing your paper ES by the SBR. For example, if your ES is 1.0 and the SBR is 5 stops (1.5) the appropriate average gradient is 0.67, which most popular materials will handle easily. But if you decide on a 4-stop SBR the result (1/1.2=0.83) may not be within range, and a 3-stop SBR (1/0.9=1.1) is more than most common materials can handle, although there are a few exceptions. If you're using the ExpoDev program it'll warn you if your chosen input values exceed the materials' capabilities.

No need to send crow feathers; I'm just delighted to hear that you've given BTZS a chance!

-- Phil

 

[Kirk Keyes]

I too was confused by this and asked Phil about two years ago. Here is his response:

Jorge - thanks for posting that. It's exactly what I was looking for.

Interesting work-around he suggested for the software. And that he mentioned rock art - as that seems to be a favorite subject for many of us out in the western US.

 

[Claire Senft]

Jdef you are correct that Davis has covered the usage of both the spotmeter as well as the incident meter and recommends both his zone system as well as the incident system. That being said the terminology SBR is a term for the incident system not for the zone system.

 

[Kirk Keyes]

Davis does not exclude the use of a spotmeter for use with BTZS...

In Kirk's example, a spotmeter seems to me the better tool for the job, requiring less interpretation and workarounds.

I'm sure Sandy's method for determining low subject ranges with an incident meter works well enough, but that is not the same as saying it works better than a spotmeter would in that situation.

Jay - I did see that Davis does discuss the use of spotmeters, and I also agree that a spot metering technique should be more accurate, as it is directly measureing the luminance range of the scene, and not estimating it as the incident system would.

I was just curious about how the other half lives when they only have an incident meter when I posed the question.

I do highly recommend the Minolta Flashmeter VI because it can do both incident and reflected metering. And even flash! It can even compare an incident measurement with a spot reading and display the difference in stops. Really neat feature. I love it! (Sekonic also makes a similar meter.)

And since the Flashmeter VI reads in 0.1 stop increments, so you actually could measure SBRs to decimal places, like 7.9 - 4.5 + 5 = 8.4 SBR.

Not that you really need that sort of precision, but you could if you wanted to...

Kirk