Dealing with luminance ranges

sanking

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Yes, SBR is indeed BTZS terminology that is based on and anticipates incident readings. SBR is not a corruption or misuse of the terms LSLR because they are not the same thing, though in some cases they may indicate the same or similar values. As has been pointed out before, a SBR reading is based on a reading of the intensity, or illuminance of the light that falls on the subject. LSLR is based on the brightness or luminosity of light reflected from the subject and is measured with a reflectance meter. Moreover, if you read carefully the pertinent sections in Beyond the Zone System it should be clear that SBR and SLR are not used to mean the same thing.

When I speak of the 5-stop range I do so within the context of the way Davis describes it, i.e. it is based on the presumption that the maximum subject luminance range of any object in a glare-free, shadow-free area, and that is evenly illuminated, is about five stops. SBR is a concept that ensues from his assumption that the subject luminance range can be estimated by adding the illuminance range (which is the difference between readings measured with an incident meter in the most brightly lit area of the scene and in the shadow areas of the scene) to the 5-stop luminance range. In other words, the SBR system of metering does not give us LSLR, but an estimate of it. In fact, it is impossible to directly measure LSLR with an incident meter at all.

My response to Kirk in the other thread offered a means of getting around the obvious fact that we can not directly measure SBR values below 5 when there is no difference in intensity in the light falling on the subject in different areas of the scene. The only way to do that is to fudge the issue by simulation.

At some place in Beyond the Zone System Davis mentions that he used the term SBR to avoid confusion with SLR, which was widely used at that time to mean a single lens reflex camera. Strictly speaking he did not need to make that clarification at all because SBR as he uses ther term is not the same as subject luminance range, or LSLR. The term SBR only has meaning within the specific reference of the BTZS system of exposure and development, which is built around the use of an incident meter and attempts to provide a fast and reliable method of *estimating* the subject luminance range.

In fact, to say that SBR is a corruption of NSLR is a contradiction in logic, for as Stephen Benskin correctly notes, “subject luminance range can be measured with a spot meter. In fact, you can only assume the range with an incident meter.” SBR is not NSLR. It is a term used with very precise meaning within the framework of a specific system or method for exposure and develoment. It incorporates some of the assumptions of NSLR but it is clearly not the same thing since, as I belive we all agree, it is impossible to measure NSLR directly with an incident meter since it is based on luminance readings. So, far from confusing terms, Davis shows much greater precision in the use of terminology than some of us contributing to this discussion, and I include myself, sadly, in the group.


Sandy
 
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Jorge

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Jorge

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The reason that referring to SBRs as function of development is not good is because it assumes a fixed ES. For example go back and read the posted results from Kirk's numbers. When I used an ES of 1.45 his SBR was 3.6, when I used an ES of 1.05 his SBR was 2.6. So if you say " I developed this film to an SBR of 9", you also have to specify the ES so that we are all talking about the same results. OTOH if you say " I develop this film to a G bar of .76" then regardless of the ES we are individually using, we all can relate the results to our own experience.
 

Kirk Keyes

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Jay - you need to remember the above - it's key to the BTZS meter with an incident meter. Davis is making an assumption in order to devise a simplified metering system. There's nothing wrong with making an assumption like that - and by many accounts, it works really well for many types of situations.

My question in the other thread was to find out what happens (incident metering-wise) when a subject fell outside of the conditions that the basic assumption covered.
 

Kirk Keyes

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sanking said:
At some place in Beyond the Zone System Davis mentions that he used the term SBR to avoid confusion with SLR, which was widely used at that time to mean a single lens reflex camera.
Click to expand...

Wouldn't SIR - "Subject Illumination Range" have been appropriate if Davis modified the system to not include the addition of "5" to the difference of all readings?

(But then it doesn't matter, as Davis is free to use any terminology he wishes. It is his system, after all.)
 

Jorge

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I think if you are discussin subject ranges then it is going to get too confusing trying to figure out if you mean this from the actual subject or a film test. While it might be obvious to you in the general context of the message, it might no be to all of us. Why not use the terminilogy as we all learned it from Phil so that we are all in the same page?
 

Stephen Benskin

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Jorge said:
Why not use the terminilogy as we all learned it from Phil so that we are all in the same page?
Click to expand...

Some of us aren't into BTZS as much as others. Why not use the terms that are used in the real world - like the recognize international terms? Like I've said before, it's fine for Davis to use any term he wishes within the BTZS community, but the use outside of the community can create confusion. That's why there are accepted terms and definitions of those terms. Those who decide on these issues don't chose them haphaserdly. There are frequently extended debates. A somewhat relevant example is with the subcommittee on colorimetry in the 1930s. It took more than 6 years for them to agree color was a psychophysical phenomenon.
 

Jorge

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jdef said:
Jorge, take this exchange for example-




Do you find the information provided confusing?

Jay
Click to expand...
The first one yes, the second one no.

In the first one you mixed SBR and CI interchangeably and it was confusing. The second paragraph is perfect, although I am a bit skeptical about a developer than can make HP5 get a G bar of 1.41. Without trying to piss you off, that is too big a slope for HP5 and makes me think there must be a mistake in your numbers somewhere, specially for a non staining developer, whatever this developer is....
 

Jorge

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I can only respond that most of us here are familiar with the BTZS, and not familiar with the more rigorous terms you are using. I dont know about anybody else here, but I cannot "place" units like meter/candle/second as well as log units.
OTOH one would hope that a discussion like this would encourage someone to try a more methodological approach to exposing and printing. The BTZS does that very well, they would have to read 10 or more books to understand the terminology you use. In my case, tha alphabet soup you use is totally confusing. The BTZS has 4 important basic abreviations, SBR, G bar, ES and DR that are easily correlated... LESR, LER, etc, etc. are unfamiliar and do not "register" with me, I get stuck thinking "now, what the hell was LESR?"....

Bottom line Beskin, you are the only one using this terminology in this forum, the rest of us are using the BTZS one. Right or wrong that is the way it is...
 

Kirk Keyes

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Jorge said:
OTOH if you say " I develop this film to a G bar of .76" then regardless of the ES we are individually using, we all can relate the results to our own experience.
Click to expand...

THis still has the problem of not matching the development to the printing process. We do know exactly how much development was given, but it will print completely different in regular silver, AZO,... But that's OK is we just mention our target material.

I do have to wonder how we did determine that the film was developed to a G-bar of 0.76 though... unless that particualr sheet of film contained a step wedge with a proper, full range of exposure.
 

Stephen Benskin

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Jorge said:
Bottom line Beskin, you are the only one using this terminology in this forum, the rest of us are using the BTZS one. Right or wrong that is the way it is...
Click to expand...

Jorge my name is included with all the posts. It's Benskin. While I don't think "because everyone else is doing it" is a good argument, I am more than capable of coverting the BTZS terms, but I cannot personally use something I feel is incorrect. So please give me the same consideration and allow me the right to use the terminology I am most familiar with. Maybe we can both learn something new. Thanks.

I cannot "place" units like meter/candle/second as well as log units

BTZS mostly uses relative log-H if I'm not mistaken. Meter Candle Seconds is the antilog of log-H. Meter Candle Seconds are used in calculating film speed and, well, exposure, i.e. B&W film speed equation is 0.8 / Hm where Hm is in mcs.
 

Kirk Keyes

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Jay, as we know, I'm no expert on BTZS, but I'll give it a try anyway!

Just keep in mind that all those BTZS graphs we are looking at where there is a SBR value given on the graph, located next to the amount of development, calculated with G-bar, the exposure scale (ES) of the printing material has been used in the calculation of the SBR. So the SBR values on the graphs, have the ES incorporated into it, they are inseparable.

So it is consitent to label the graphs with the SBR - but when we talk about it, we need to make sure we mention the ES as well.
 

Jorge

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Sorry, but you are wrong, at least when we talk about the BTZS. Once again, to use the numbers you posted in the other thread. For an ES of 1.05 you had an SBR of 2.6, for an ES of 1.45 you had an SBR of 3.6, yet for both the G bar was 1.31. with the relation G=ES/SBR, you can adjust wichever way you want.
 

sanking

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What you apparently fail to understand, or refuse to recognize, is that there *is* no internationally accepted term for SBR as it is explained and used in Davis’ BTZS system. SBR, as Davis uses the term is not the same as LSLR. SBR only has meaning within the specific reference of the BTZS system of exposure and development with an incident meter. It is based on an assumption, i.e. that the subject luminance range can be estimated by adding the illuminance range (which is the difference between readings measured with an incident meter in the most brightly lit area the scene and in the shadow areas of the scene) to the 5-stop luminance range. It can not be called the same thing as LSLR because, as you yourself have correctly stated, LSLR can only be measured directly with a reflectance meter, not with an incident meter.

BTZS and the Zone System are both closed, self referencing systems. Each has a language with meaning only within the context of the system. What, for example, would the concept of zonal placement mean to someone who, though a master of sensitometry, knew nothing about the Zone System?

Sandy
 

Kirk Keyes

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Jorge said:
with the relation G=ES/SBR, you can adjust wichever way you want.
Click to expand...

I was trying to point out that, better explained with your equation, rearrainged a bit, that SBR=(ES/G).

So I think what I was trying to say was "you have to state both ES and G to correlate it with SBR". (Thanks for reminding me of the formula.)
 

Kirk Keyes

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Stephen Benskin said:
A somewhat relevant example is with the subcommittee on colorimetry in the 1930s. It took more than 6 years for them to agree color was a psychophysical phenomenon.
Click to expand...

I'm sure there were still some members of the commitee that disagreed!
 

Jorge

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YOu can use whatever you want, you asked why we did not use the terminology you are using and I tried to respond.....no skin off my nose, I will simply ignore your responses because I dont understand them......just look at your last paragraph, you came up with the 0.8/Hm, where did you get that number? are supposed to take your word for it? And then I have to "see" the antilog of Log-H...sorry, just too difficult....
I am sure that you are correct in citing this number, but it just makes discussing anything with you much more difficult.

Sadly, once more this thread is widing down into another circle jerk. Instead of arousing the curiosity of the rest of the membership at APUG it is probably making them think we should stop wasting bandwidth and go take pictures...

Since I am going to keep on using the "incorrect" BTZS nomenclature, I guess I have nothing else to add.
 

Kirk Keyes

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Jorge said:
I dont know about anybody else here, but I cannot "place" units like meter/candle/second as well as log units.
Click to expand...

When figuring out exposure for step wedges with the enlarger, I prefer to use my incident meter with a flat diffuser. The owners manual then has a conversion table to "lux-seconds", these are the same units that Kodak often uses on their H&D curves. Converted to logs, of course.
 

Jorge

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Kirk Keyes said:
I was trying to point out that, better explained with your equation, rearrainged a bit, that SBR=(ES/G).

So I think what I was trying to say was "you have to state both ES and G to correlate it with SBR". (Thanks for reminding me of the formula.)
Click to expand...

I dont think you have to state both. Lets take jdef's example for instance, he developed HP5 to a G bar of 1.41....from that I can deduce the SBR for my system I simple have to plug in 1.45, In your case you would plug in 1.05 in jdef's case he uses 1.7 for ES. As I said, the G bar does not change.

Let me just give you Phil's interpretation:

In other words, assuming ES is constant, you can develop for either G or
SBR. I prefer to target G, however, because it expresses the _relationship_
between ES and SBR without requiring them to be defined specifically.
 

Kirk Keyes

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Jorge said:
In other words, assuming ES is constant,
Click to expand...

Right - that's what I was trying to point out. When we are all using different materials, then it is not so clear unless we state the materials being used.
 

Stephen Benskin

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I look at BTZS as tone reproduction with some Zone terms. I can accept however you want to apply it. I can also respectfully disagree with it too. We can argue that Davis writes that "SBR" is his abbreviation for Subject Luminance Range, but what's the point? I think it's possible to communicate our ideas without coming to an agreement on terms.

I've place Naturalistic Photography for Students of the Arts on my reading list. Thanks for that.

As for the question:
Here's an interesting question. Except for special cirumstances, all scenes look best in a print when there is a full range of tones. Why can't we let a flat scene remain flat in the print (apart from artistic considerations)? It's flat in nature, why not the print?

Part of the reason is psychological. It falls under the heading of visual adaptation, and more precisely the area of lateral adaptation, and perhaps falls within simultaneous contrast. Every photographer has experienced at one time or another photographing a scene on an overcast day and being disappoint by the flat results. The scene looked fine when photographing it. What happen? For various survival purposes, it's important to be able to distinguish elements in a scene as clearly as possible. So our brain wants to adjust every scene so that it has as full of a range as possible. That's why the scene looked good to the photographer and came out flat on the film. And I believe that is why we want to see a print with the full range of tones.

Back to the topic of the thread. One of the images in the current issue of PHOTO Techniques required something new for me. The subject was the stone work in Peterborough Cathedral. The camera was pointed up toward the ceiling. Strong ambient light was coming in from a bank of windows and illuminating the lower columns, and the ceiling remained in shadows. The luminance range was around normal, but not only was the balance of tones not aesthetically pleasing, there was little tonal seperation in the stone work.

If I pushed the film, the tones on the lower columns would be increased further unbalancing the tones, and the local contrast in the stone work would change little. Masking was an option. I figured it would take approximately four or five seperate mask to accomplish the look I wanted. I needed to hold down the columns while I brought up the ceiling. I needed to increase the local contrast over the entire image with an additional increase in the ceiling. There were a few touches that could also be accomplished by bleaching.

I could either go the complicating masking route or try something different. I chose to go digital. Digital is just another tool. I had the negative scanned, worked on it in Photoshop (just using the tonal controls - no cutting and pasting) and then had it output on a negative. It now has the look I want and is almost capable of a straight silver print.
 
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Stephen Benskin

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Why is everything a fight with you. You were the one to bring up using only BTZS. I replied why not real sensitometric terms. I then agreed that people shouldn't have to change the expressions they are comfortable in using. I can adjust to BTZS terms and I hope people can adjust to me. If you wish to ignore me, please do. I don't like to fight over everything.

As for the equation, I said it is the B&W film speed equation. Why would I lie about that?

As for the thread winding down, I believe I am the only person who has responded to the original question about different ways to deal with various luminance ranges. It's a potentially interesting subject if you would like to participate.
 

Donald Miller

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I have been watching this thread with interest. It seems to me that rather then dealing with differing scene luminance ranges it has once again degenerated into the usual discussion over the use of proper terminology.

To that I say HO HUM....

It seems to me that several who have a peliminary knowledge of BTZS have found that they want to re-interpert the terminology that system uses and to reinsert new terminology into that system.

Now I have no problem with those who want to call something other then what the general mass of the users of that system utilize...so long as they don't expect the general mass to communicate to them with the ammended terminology...That desire would seem to be to be the height of arrogance.

Interesting that with rather minor exceptions no one has really talked about dealing with differing luminance ranges. The one example given utilized digital process and I find that interesting.

Now I will step aside...put a number of you back on my ignore list and wish you well.
 

Kirk Keyes

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Donald Miller said:
It seems to me that several who have a peliminary knowledge of BTZS have found that they want to re-interpert the terminology that system uses and to reinsert new terminology into that system.
Click to expand...

Donald! Good to see you! Glad you made it.

I think we are just trying to figure out how to fit the BTZS terminology into our world view.

But anyway, it would be better to get back to Jay's original question.
 

Donald Miller

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Stephen Benskin wrote "Here's an interesting question. Except for special cirumstances, all scenes look best in a print when there is a full range of tones. Why can't we let a flat scene remain flat in the print (apart from artistic considerations)? It's flat in nature, why not the print?"



While you would certainly be entitled to your viewpoint...I heartily disagree...
A print can look stunning without the full range of tones provided there is adequate local contrast.
 
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