# BTZS 0,5 ZS 0,57 Why?

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• 02-12-2013, 08:30 PM
AndreasT
Quote:

Originally Posted by Stephen Benskin
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.

Yes I relied on this quote. I never did this test myself and never really considered flare much. Well I never really had a problem with it because I always used the "corrected" methods by others. It only became an issue because of getting involved with BTZS.
And because I started reading the posts of MR Benskin. Grrr...
I need time for this to sink in.
• 02-12-2013, 08:39 PM
AndreasT
Flare affects the optical image and not the film curve.
How do I apply flare to my plotted curves. I am having a hard time getting there. Basically my pure clean curves are lying to me.
• 02-12-2013, 08:49 PM
AndreasT
Do you mean Photographic Materials and Processes by Leslie Stroebel? It has 608 pages!!
• 02-12-2013, 09:09 PM
Bill Burk
Quote:

Originally Posted by AndreasT
Flare affects the optical image and not the film curve.
How do I apply flare to my plotted curves. I am having a hard time getting there. Basically my pure clean curves are lying to me.

Well you could do what I do. Pick a flare value that you believe applies to your system. I say 0.4 Log Exposure Units.

At an appropriate part of the curve (and this is where I just throw darts and start where the curve crosses 0.1 density on the non-flare test plots), identify the exposure. Now identify the exposure at 0.4 Log Exposure Units to the right.

Take the difference*. Add that amount (call it flare exposure) to the exposure for each plotted point. Look at the original graph to see what density you get for the summed exposure (original plus flare exposure*). Plot that density point directly above the original plotted point.

As you move to the right, the flare exposure becomes logarithmically less significant, so the new curve will taper.

Sounds awful, maybe someone can explain it better than me.

*Get the antilogs so you are summing arithmetic values and then get the log of that sum
• 02-12-2013, 09:22 PM
AndreasT
Thanks all, it is 3:21 AM, time to stop for today. Will be getting back to this.
• 02-12-2013, 10:03 PM
Michael R 1974
Quote:

Originally Posted by markbarendt
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.

The x-axis, in my opinion, is always where things get confusing. I like to think of the increments on the x-axis of a H&D curve (regardless of how it is labelled) as relative "camera exposure settings". I think this might be analogous to what you refer to as "placement". In a zero-flare, calibrated system, actual exposure = expected exposure. When there is flare, actual exposure > expected exposure. In the lower values, densities are raised and local contrast is reduced. This is one of the problems with the typical ZS camera test in which we meter a card and stop down 4 stops.
• 02-12-2013, 10:07 PM
Stephen Benskin
Quote:

Originally Posted by AndreasT
Do you mean Photographic Materials and Processes by Leslie Stroebel? It has 608 pages!!

Yes, but you don't have to read the parts on color. The chapters that relate to this discussion are Photographic Sensitometry, Camera and Printing Exposure, and Tone Reproduction.

Sensitometry for Photographers is a nice book on the practical use of sensitometry. There's also Todd and Zakia's Photographic Sensitometry.

Quote:

Well I never really had a problem with it because I always used the "corrected" methods by others.
If you look closely, most haven't really corrected for flare as much as they have ignored it.

Quote:

How do I apply flare to my plotted curves. I am having a hard time getting there. Basically my pure clean curves are lying to me.
You don't need to plot flare in order to incorporate it. You already know how to factor it into development determination. LSLR - Flare
• 02-13-2013, 06:09 AM
markbarendt
Quote:

Originally Posted by Michael R 1974
The x-axis, in my opinion, is always where things get confusing. I like to think of the increments on the x-axis of a H&D curve (regardless of how it is labelled) as relative "camera exposure settings". I think this might be analogous to what you refer to as "placement". In a zero-flare, calibrated system, actual exposure = expected exposure. When there is flare, actual exposure > expected exposure. In the lower values, densities are raised and local contrast is reduced. This is one of the problems with the typical ZS camera test in which we meter a card and stop down 4 stops.

I agree that the ZS has issues.

Overnight it clicked that "the construct" is Stephan's camera image quadrant where he is using (subject) reflectance to define the x axis scale.

The thing that was new in concept to me was that on a standard H&D curve, image compression on the straight line of the curve is possible. I had thought that the H&D curve was a better visual representation of what was happening in the image in real life than it really is.

Seeing the curve tied to the subject mater in the camera image quadrant gives me a much more relevent representation of what's happening to my print. Like the negative itself, the film's curve shape is only important as a reference guide to a storage device, a map of where it is holding the info about certain tones.
• 02-13-2013, 09:36 AM
Michael R 1974
Quote:

Originally Posted by markbarendt
I agree that the ZS has issues.

Overnight it clicked that "the construct" is Stephan's camera image quadrant where he is using (subject) reflectance to define the x axis scale.

The thing that was new in concept to me was that on a standard H&D curve, image compression on the straight line of the curve is possible. I had thought that the H&D curve was a better visual representation of what was happening in the image in real life than it really is.

Seeing the curve tied to the subject mater in the camera image quadrant gives me a much more relevent representation of what's happening to my print. Like the negative itself, the film's curve shape is only important as a reference guide to a storage device, a map of where it is holding the info about certain tones.

This was the basis for my for my assertion that reducing exposure in a high flare situation only results in more of the subject range being compressed, or that the increased toe density associated with flare - usually referred to as an increase in effective speed - is of little use.
• 02-13-2013, 09:52 AM
markbarendt
Quote:

Originally Posted by Michael R 1974
This was the basis for my for my assertion that reducing exposure in a high flare situation only results in more of the subject range being compressed, or that the increased toe density associated with flare - usually referred to as an increase in effective speed - is of little use.

Yep, as soon as I got the concept the logic for your assertion "popped" too, makes perfect sense now.
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