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# Thread: BTZS 0,5 ZS 0,57 Why?

1. Originally Posted by Stephen Benskin
Working with them and writing the program made the theory tangible. It really clarified things.
I've had that experience with various subjects, one of the most fun was programming a TI calculator to do spherical trigonometry for flight planning.

I'm actually trying to write a concise piece on using light meters, even though I understand the use quite well, trying to explain it clearly to a general audience is a a challenge and helping me refine my understanding even more.

2. Originally Posted by AndreasT
OK, ok, I am going to work through this. Concerning abbreviations what do you mean by LSLR? LER is the paper contrast value?
LSLR and LER are the correct terms. Davis uses IDmax and SI. Scale is no longer used. Davis only kept these terms because he didn't want to make changes to the plotting program. There's even a disclaimer in the fourth edition. Some of the terms are dated and some he made up. It's frustrating when referencing BTZS with other material.

He mentions a small flare amount of 0,02 as a starting standard. What you (Stephen) say is much more.
Another problem with systems. If I remember correctly, Davis is referring to the density difference to the film curve as caused by flare. One, he applies the effects of flare to the film curve. This is an old approach which is more of a construct than reality. Flare affects the optical image and not the film curve. Two, his calculation is more of an approximation of the influence of flare. He doesn't use the flare equation. Or in other words a system.

If you really want to understand sensitometry, you need to read something more academic. Photographic Materials and Processes would be an excellent start. Theory of the Photographic Process 3rd edition is a little more advanced.

3. Originally Posted by markbarendt
I'm actually trying to write a concise piece on using light meters, even though I understand the use quite well, trying to explain it clearly to a general audience is a a challenge and helping me refine my understanding even more.
From what I understand, this is what teachers go through. It's also one of the reasons why I participate in these forums.

4. Originally Posted by Stephen Benskin
Working with them and writing the program made the theory tangible. It really clarified things.
What programm?

5. Originally Posted by Stephen Benskin

If you really want to understand sensitometry, you need to read something more academic. Photographic Materials and Processes would be an excellent start. Theory of the Photographic Process 3rd edition is a little more advanced.
What bothers me about a lot of this is the explanation in many books and articles. They are sometimes difficult to follow. Ansel Adams I found labourous especially when trying it out for the first time. Personally for me the best method of explanation I have read is "Way Beyond Monochrom"
Phil Davis I read after WBN and he jumped around too much with his explanations.
I have been reading up a bit today of Phil Davis and I think some of the fog is starting to lift understanding his method. I have been using the "Way Beyond Monochrom" method for years and it worked, resulting in me reading BTZS less thorough.
Anyway Stephen I will be reading up on some of yours posts as well, you cover this subjegt a bit.

6. Originally Posted by AndreasT
What programm?
The four quadrant reproduction curve example from a few posts back is from a program I wrote.

7. I envy people who can do that.

8. Originally Posted by Stephen Benskin
...... One, he applies the effects of flare to the film curve. This is an old approach which is more of a construct than reality. Flare affects the optical image and not the film curve. Two, his calculation is more of an approximation of the influence of flare. He doesn't use the flare equation. Or in other words a system.
Even though it is a construct won`t it work. At least in part. I see your Practical Flare Model is very close to the Way Beyond Monochrom numbers as well as The Zone System number.
Flare always seems to just get a footnote.
I have the BTZS PLotter programm by the by. Have been playing around with it today, with the flare part and I think I am getting the hang of it.
However those flare numbers are difficult to swallow seeing how high they are.

9. Originally Posted by Stephen Benskin
...If I remember correctly, Davis is referring to the density difference to the film curve as caused by flare. One, he applies the effects of flare to the film curve. This is an old approach which is more of a construct than reality. Flare affects the optical image and not the film curve.
Interesting. So thinking out loud here... If I get the concept here, flare actually compresses the shadows on the original line of the curve. Even though we are moving into steeper parts of the curve flare is still compressing the tones.

It seems to me then that essentially the construct you speak of is that the normal log exposure vs density curve is replaced by a scene zone placement vs density scale. Even if not perfect is that a reasonable understanding?

If true that almost seems like a better way to visualize what is going to print. It becomes a labeling issue instead of a technical flaw. Seems to me that the log exposure vs density model hides flare's effect.

10. Originally Posted by AndreasT
Even though it is a construct won`t it work. At least in part.
Of course if works. That's not what is in question. It can lead to a misinterpretation of how the process works. Anyone viewing such a curve is required to be aware what it represents.

I see your Practical Flare Model is very close to the Way Beyond Monochrom numbers as well as The Zone System number.
Flare always seems to just get a footnote.
The results are close, but the variables are different. Only one of the three models use variables that describe reality. Both the Zone System and WBM basically use what Davis calls the effective density range. Problem is, neither explains this is what they are doing. My Practical Flare Model is derived by averaging the values from the fixed flare model and variable flare model. While the variable flare model has the potential to be the most accurate. Matching the NDR to the paper LER is less an indication of quality as the luminance ranges progressively increase or decrease. I believe my approach tempers the extreme ranges and tends to fit the preferred NDR to LER relationships.

However those flare numbers are difficult to swallow seeing how high they are.
That's the funny thing about facts, they don't care if you believe them or not. Seriously, before you judge, study up on the subject. What I believe you are referring to when you said 0.02 density increase is from the black box test described in BTZS. You appear to be confusing density increase from flare and the amount of flare. Also, I can't see the black box test as more of an exercise to create an impression of flare's effects and not an actual measurement. I did a similar black box test. Around the opening of the box, I place various targets, black, gray, checkerboard, and white. Below are the results. While there is a difference in density of 0.09 between the black target and the white target, the difference in exposure is 0.39 of 1 1/3 stops.

On page 94 of BTZS, Davis recommends adjusting the SI by 10% for the effective DR in order to compensate for flare. For a NDR of 1.05, 1.05 * 1.10 = 1.15. The gradient for a log 2.20 luminance range would then be 1.15 / 2.20 = 0.52. If we take the unadjusted NDR of 1.05 and apply it to a log 2.20 luminance range minus flare, how much flare would it take to to equal 0.52? 1.05 / (2.20 - 0.20) = 0.52 or 2/3 stop flare.

This is how flare really works.

And for the Zone inclined:

Here's an example of the effect on both the shadow exposure and the effective luminance range over a range of flare. In this example the no flare curve produces an effective luminance range of 2.20.

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