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Just to be clear, the note along side of point 5 stating "Statistical average scene with equivocal gray calibration surface" doesn't refer to 18% gray. Under the statistically average conditions,...

It actually does. That is what Holmes meant when he referred to the importance of knowing the values and their relationships. The relationship between Hm and Hg (Hm/Hg), points 4 and 5 on Dunn's...

True, it is theory, and I find understanding theory helps to avoid misconceptions. Adam's K factor conspiracy rant in The Negative is a good example. The exposure meter seeing 18% gray is another. ...

Real quick on K. K is a constant used in the calibration of exposure meters. It can be considered a light loss constant.

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Within the K equation are the elements of the equation to...

There are two ways of thinking about film speed, speed as a property of a photographic emulsion, and speed as a practical approach to have as an index to enter into a meter.

From Jack Holm,...

Jones was the first to approach the determination of film speed using psychophysics. Previous film speed methods were generally based on an assumption of a characteristic of the film curve. As...

Something else to keep in mind, the full range needs to be within the meter's field of view (spot meter because it has an optical system to create flare). If you are measuring a small dark area and...

I would like to emphasize Bill's spot meter flare came from a scene with a full luminance range and not from a test target.

The Zone System didn't change with the change in the speed standard. ...

Sorry, I spent around two hour writing a post and when I went to upload it, the site had logged me off and I lost 95% of it. All that survives is the bit of intro below. Not really in the mood to...

Pere, where to start. First, think of the parameters of the ISO speed graph as no more than how to determine a gradient, not unlike other methods like Contrast Index or average gradient. All three...

Hi Pere, I'm getting ready for work, so let me throw this out for now and I'll go into more detail later. n does not equal the meter calibration point. The contrast parameters are part of an...

Forgive me if I've misinterpreted the above sentence, but the ISO B&W Speed Diagram isn't about exposure range or underexposure. It is an illustration on how to determine b&w negative film speed. ...

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Thanks Bill for using the term Subject Luminace Range.

It's all fine as long as there is awareness. Otherwise, not only can it potentially be a waste of time and materials but also counter productive.

Agreed. I think it's partly because most people don't hold a clear definition of "film speed"; and partly because most aren't actually interested in what is film speed, but only how to achieve...

Doremus,

That's because it seems to take about a year of badgering for someone to believe me. :)

Panoral, below is an example of a four quadrant reproduction curve. Notice how the original luminance range of 2.20 is reduce within the camera, by flare, The film is processed so that the...

What I am talking about is theory (Exposure and Tone Reproduction). The math is there to explain it. Just like the Zone System (simplified Tone Reproduction Theory), understanding how the process...

12% Reflectance, not 18% Reflectance. Please refer to the defining K compliation.

The math is there as a proof. Without it, the 12%/18% debate could go on forever. I've shown that meters "see" 12%. You don't need to use the math, but you should incorporate the conclusion.

Let me know what you don't agree with and we can have a discussion. If it's about exposure meters, you can find the answers in D. Connelly, Calibration Levels of Film and Exposure Devices.
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It's a well designed site. Since you are introducing it on a technical forum, I thought you might like some technical feedback. You use ASA when you should be using EI. Meters don't "see" 18%...

I'm having trouble finding it over there too. Unfortunately the file is too large to upload here. Send me your email address in a private message and I'll email it.

Here are a few examples of Zone Placement on a paper curve.

Example 1. Equally spaced along log-H axis. Zone I and Zone VIII falling on the ISO 90% D-Max and 0.04 over Fb+f LER criteria.
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Not sure if anybody has had the chance to look over the spreadsheet, but by you can also see what grade of paper a "normally" developed negative will need to print on depending on the subject...

I've put together a spreadsheet that determines the aim contrast index from the subject luminance range and paper LER for a diffusion enlarger. This is based on my practical development model as...

Interestingly enough the apparent difference in aim density ranges between Adam's Zone System and the ISO standard's is mostly an illusion. It's a matter of how the data is presented and whether or...

If you are looking for an accurate interpretation and if you are using a step tablet, post the resulting densities for each step. Indicate if they include Fb+f and if they do provide the Fb+f value....

There isn't enough information for me to make any judgements based on density. Mario doesn't give precise values but ranges, and he doesn't mention if the values include Fb+f or not. In general, I...

Here are the numbers from the four quad example.

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The paper LER is the log exposure range between the points of 90% of the paper D-Max and a paper density of 0.04 over paper base plus fog. This range can be considered Zone I to Zone VIII. As you...

What causes the difference between different types of enlargers is called the Callier Effect. It has to do with how parable the light is as it strikes and passes through the negative. Condensers...

Do not just rely on The Negative to explain sensitometry and tone reproduction. There are a number of books that are more focused on that topic. The Zone System uses a simplified form of tone...

They are negative densities. The range has to do with matching the negative density range (NDR) to the print log exposure range (LER). Without knowing the paper's LER, you can't determine the...

Here are a couple of pages from the ANSI Photographic Exposure Guide - ANSI PH2.7-1986. It gives the Incident Values for different Latitudes for different times of days and throughout the year. The...

Sunny 16 is connected to the variables in the exposure equation. This is an excerpt from the APUG thread "Is the K factor relevant to me or should I factor it out." The title is about middle gray...

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I brought up Delta-X as a question of the practicality of doing a speed test for most people. It's unrealistic to expect valid speed results without a sensitometer and proper methodology. The best...

Bill, we both forgot to mention that speeds derived from using the fixed density point of 0.10 over Fb+f are only accurate for "normal" using the ISO standard's contrast parameters.

Most of my paper curves incorporate flare. Instead of contacting the step tablet, I usually enlarge the test. I don't want to have to add more quadrants.

From a tone reproduction basis, Jones...