Film test results

[Stephen Benskin]

In testing, it's important to control the variables. When doing a film test, you want to determine the characteristics of the film, so you need to eliminate everything else that can skew the results. In order for the testing results to be applicable to practice, you need to factor back in the variables.

[Bill Burk]

I was looking at one of my sensitometric tests of a 100 speed film which I consider a solid benchmark of film characteristics. At some point of one of the curves the density crosses 0.10, which I deduce corresponds to -2.1 Log MCS exposure. And based on discussions so far, if I were to make a camera test and obtained a similar negative, assuming all is well, the meter using standard calibration would be reading -1.1 Log MCS.

But that's not where Zone System calibration would be. Zone V would be 4 stops from the 0.1 point (which you may recall is at -2.1 Log MCS). Just counting from that point up is -0.9 Log MCS... Two-thirds' stops out to the right. Aside from recalibrating, the obvious way to get the meter to show the shutter speed and f/stop combination that I just used for that negative... would be for me to set the meter to indicate the -1.1 Log MCS... And to do that I would set the meter at Exposure Index 64

So there's 2/3 stop downrating for Zone System right there, which is also 2/3 stop different from Incident reading.

[Stephen Benskin]

Bill, that is basically changing the value of n₁ (difference between speed point and metered exposure point) from Δ1.00 log-H to Δ1.20. The attachment has the EI at half the film speed or n₁ = Δ1.30 log-H. For a 125 speed film, the metered exposure should be 0.064 lxs.

[Bill Burk]

Right Stephen,

That's what I see happens when you use Zone System metering, to place and "test" for Zone I shadows to be 0.10 density in a low-flare test (stopping down 4 stops from meter reading). This is widely corroborated (that you have to rate film 2/3 to 1 stop less than box speed). Many people who have done Zone System camera tests determine that their system, all variables included, require this 2/3 to 1 stop change from rated speed (change of n-sub-1 from standard calibration Δ1.00 log-H to zone system compatible Δ1.20 or Δ1.30).

So it's apparent to me that 2/3 stop of this change comes from the counting of Zones itself. The distance to the metered point Zone V to the tested Zone I is four stops 1.20

[Stephen Benskin]

As shown in a previous post, the average gradient for Zone System Normal for a diffusion enlarger is 1.25 / 2.1 = 0.59. So what should the gradient be for a NDR of 1.05?

1.05/2.1 = 0.50

Kodak uses a contrast index of 0.58 for aim NDR of 1.05. They also use a subject Luminance range of 2.20. Is that the difference?

1.05/2.20 = 0.48

No. Then how can the Zone System with an aim NDR have an average gradient of 0.59 with is almost identical to a Kodak's CI 0.58 for an aim NDR of 1.05? Obviously something is missing. The equation contains the subject, development, and the resulting negative (to match the print).

If the equation is supposed to represent the results from the variables in the photographic process, what is missing is the camera. Sensitometric testing uses a contacted step tablet to to eliminate the variables of the camera and determine only the characteristics of the film. Those variables need to be factored back in when evaluating how to use the film in shooting conditions.

Even though the Zone System utilizes a camera in testing, the method of testing doesn't represent shooting conditions either.

[Bill Burk]

I'm accustomed to reducing the subject Luminance range by 0.40 to account for flare

This would make 1.05 / ( 2.20 - 0.40 ) which is 0.58

Or I could choose a 2.1 subject Luminance range and then it would become 1.05 / ( 2.10 - 0.40 ) which is 0.62

[stawastawa]

Since the zone system testing tends to set up grey cards or 'evenly lit subjects' to shoot and represent at various levels of gray it is creating an artificial scenario. The test results show film characteristics specific to that situation and style of metering. I'm guessing the zone system methods aren't properly accounting for the subject bright range. But I would think that could be specified to be similar... People do their testing with the idea of a zone IX or zone X for pure whites. Similar to how alternative process users know their medium has a wider contrast range, yes?

The zone system is supposed to take into account the camera and metering style of the individual... you are saying this is not so?

When ever I start thinking seriously about doing some zone system tests I think I had better find a nice contrasty subject with broad surfaces to meter extensively and compare notes after shooting and developing in several different manners. and that time is long over due =)

[Leigh]

Since the zone system testing tends to set up grey cards or 'evenly lit subjects' to shoot and represent at various levels of gray it is creating an artificial scenario. The test results show film characteristics specific to that situation and style of metering.

The film knows and cares absolutely nothing about the subject.

The film's assigned task is to render specific tonal values as specific densities, period.

The concept of an "artificial scenario" is specious. Anything in front of the camera lens is a valid subject.

- Leigh

[stawastawa]

anything is valid, but the zone system tests are setting up a situation, baseline, that will then be used as a guide for shooting a variety of scenarios. Does that guide fit the scenes it is designed to be used for? why is it that both the zone system and kodak have guidelines for shooting, developing and printing on grade 2 paper. ZS uses slightly different shooting and development. why?

(I am now just reiterating Stephen's question)

[Leigh]

The fundamental error is thinking that ZS represents some universal truth.

It does not.

It is an attempt to document the workflow of one particularly successful photographer.

ANY system will provide consistent results if it is calibrated initially, and followed conscientiously.

The problem with ZS, which causes most of the confusion and arguments, is its use of human perception.
Different people see the same scene differently for various reasons, one of which is color blindness.

Almost 50% of the male population suffers from some degree of color blindness.
So surfaces of exactly the same reflectance but of different hues may be seen very differently.

- Leigh