BTZS and low contrast scenes

[sanking]

I've made a spread sheet that performs the calculations as layed out in the book.

Thanks for the correction on the terminology. And your sentence above is exactly the kind of terminology I was trying to convey in the "CI of blank film" thread recently. You CAN develop film to a given SBR, just as you can develop film to a given CI. Even if the film didn't recieve a full range of exposure, like in the case of low contrast scenes - say 3 or 4 SBR, or even scenes with no contrast, such as a blank sheet of film.

This is a false analogy in my opinion. SBR refers to subject lighting conditions and is not in any way dependent on either exposure or development. CI is a slope created by minimum and maximum densities that is measured after development and results from both exposure and development. It might be ok to say that one can develop to an anticipated CI, but to say that one can "develop film to a given CI" when the final result is not the CI to which one is developing is not reasonable. One can develop for a given SBR and may or may not get the desired CI, but the SBR has its own reality, i.e. it existed apart from and outside of the reality of the desired contrast. CI has no reality beyond its realization. If you develop to a CI and get some other slope than what was intended then what you have is another CI.

Sandy

[sanking]

You CAN develop film to a given SBR, just as you can develop film to a given CI. Even if the film didn't recieve a full range of exposure, like in the case of low contrast scenes - say 3 or 4 SBR, or even scenes with no contrast, such as a blank sheet of film.

Kirk,

Or let me put it another way. OK, so you decide to "develop your film to a given CI", but after development you discover that the CI is different from the one to which you "developed your film."

OK, to what CI did you really develop your film? And is that question different than asking, "to what CI was your film developed"?

In my opinion the matter is really very simple. The statement "develop the film to a given CI, " which apparently exists in the literature, is improper and confusing use of the language. Or most charitably, an abbreviation assuming the reader would understand that what was really meant was that one should "develop for a time that would produce a given CI."

Sandy

[dancqu]

CI has no reality beyond its realization.

So a CI is the result. This + that x something else = result.
Could you fill in just what the this, that , and something else
might be? Likely, a constant or two, k values, are involved.
Don't forget the givens. Dan

[Donald Miller]

I've made a spread sheet that performs the calculations as layed out in the book.

Thanks for the correction on the terminology. And your sentence above is exactly the kind of terminology I was trying to convey in the "CI of blank film" thread recently. You CAN develop film to a given SBR, just as you can develop film to a given CI. Even if the film didn't recieve a full range of exposure, like in the case of low contrast scenes - say 3 or 4 SBR, or even scenes with no contrast, such as a blank sheet of film.

SBR is the contrast inherent within the scene. Development (developer, time, temperature and agitation) determines the CI one strives for consistant with the printing materials or process.

CI is the result of the inherent scene contrast, exposure, and development of the negative.

It is absolutely impossible to achieve a CI above zero if you have no exposure as in your example of a blank sheet of film.

[Kirk Keyes]

If you have the winplotter software, I would be happy to provide the raw data, so that you can plot the cuves for yourself, and see all of the data that program generates.

Here's my data for the Acros if anyone with the Winplotter software would care to crunch it for me.

Fuji Acros, Xtol 1+1, 30 minutes, 20C. I get an SBR of 2.95, and a gradient of 1.19.

Step Tablet density, film density measured with blue channel
0.05, 3.59
0.19, 3.35
0.32, 3.17
0.46, 2.98
0.60, 2.84
0.75, 2.67
0.89, 2.49
1.02, 2.31
1.18, 2.11
1.33, 1.93
1.46, 1.79
1.58, 1.63
1.73, 1.44
1.88, 1.24
2.02, 1.04
2.16, 0.84
2.30, 0.60
2.43, 0.45
2.59, 0.30
2.73, 0.20
2.87, 0.16
b+f, 0.09

[Jorge]

Donald,

Are you familiar with BTZS? There is a procedure by which the SBR can be extracted from a curve produced by printing a stepwedge onto the film in question, and reading the resulting densities with a densitometer, and plotting them against the densities of the stepwedge itself, which represents the luminance range of a theoretical scene. The resulting SBR value is often not an even number. By processing identically exposed films to varying extents, a range of SBR values results. SBR is just one value of many that can be targeted.

Jay

This is wrong. SBR was defined correctly by Don and it is the inherent contrast range caused by the illuminance in the subject. When you plot identically exposed films to different times you obtain a range of what Davis calls average gamma, not a range of SBRs. If you wish, you can then plot SBRs against average gamma to obtain a correlation. SBR is not a value you can target, IOW you cannot say I am going to develop for an SBR of 6. AT least not in the way Davis has explained the BTZS.

[Donald Miller]

Donald,

I do have a densitometer, and I can post the curves, although I don't have the Winplotter software, and must use Excel, with which I am not very familiar. If you have the winplotter software, I would be happy to provide the raw data, so that you can plot the cuves for yourself, and see all of the data that program generates. One caveat; I use a 31 step wedge calibrated in .1 density increments, and I don't know wether or not Winplotter can process that data.


Jay

Jay, Why don't you post the numbers that you have and I am sure that someone here will be able to verify your results. I am really interested in this in light of my experience with HP5.

[Jorge]

Here's my data for the Acros if anyone with the Winplotter software would care to crunch it for me.

Fuji Acros, Xtol 1+1, 30 minutes, 20C. I get an SBR of 2.95, and a gradient of 1.19.

Step Tablet density, film density measured with blue channel
0.05, 3.59
0.19, 3.35
0.32, 3.17
0.46, 2.98
0.60, 2.84
0.75, 2.67
0.89, 2.49
1.02, 2.31
1.18, 2.11
1.33, 1.93
1.46, 1.79
1.58, 1.63
1.73, 1.44
1.88, 1.24
2.02, 1.04
2.16, 0.84
2.30, 0.60
2.43, 0.45
2.59, 0.30
2.73, 0.20
2.87, 0.16
b+f, 0.09

SBR 3.6
average gamma 1.33

These are results for a paper scale of 1.45, for silver the SBR would be much lower.

[Kirk Keyes]

The important thing to understand about the scene you describe is that neither a reflected reading nor an incident reading will give you the correct exposure to reproduce the tonal values as you want them without interpretation.

I agree completely. Anytime you are shifting tones away from a direct approximation of the original scene requires interpretation. Never said otherwise.

One option is to go to one of the shadow areas of the scene and take a meter reading at that spot, note how much this EV values differs from the EV value of the first reading, and subtract from the SBR of 5 to give you a new SBR value, which could be 3 or 4. If there is not a real shadow area large enough to use for the reading you can simulate the shadows by shading the cone of the meter, take a reading, and then do the same calculation as above. Base exposure on an average of the shadow (or shaded) reading and the reading taken in full light. Or you could just double the EFS of the film and make the exposure based on the shadow reading.

Thanks for this technique - this is what I'm asking about. However, I'm not sure about it. I had no shadow areas with the sand pattern or the rock art. I guess I'm not visualizing what you are suggesting to do - here's what I think you are suggesting:

1) I have a subject with no shadow areas, one that is of low contrast.
2) Take a reading in the sunlight with the incident meter at the subject.
3) Take a second reading in the shade of my hand.
4) Subtract the two readings.
5) Exposing with the average reading.

This seems like a kludge. Is there a basis in the BTZS method for this, or just something that has been found to work fairly well? It seems like you could get a lot of variation based on how much you cover the meter sensor with your hand.

[Kirk Keyes]

SBR 3.6
average gamma 1.33

These are results for a paper scale of 1.45, for silver the SBR would be much lower.

Jorge, thanks! I should have mentioned my paper scale - sorry. I use 1.05. Could you re-crunch them?

Kirk