Why is Zone System EI often about half rated ISO/ASA?

[AndreasT]

Yes, what does that mean Bill? Use around-about box speed or use the ZS EI. If the Iso gives us shadow detail of 0.1 that should be fine

 

[Bill Burk]

Yes, what does that mean Bill? Use around-about box speed or use the ZS EI. If the Iso gives us shadow detail of 0.1 that should be fine

Since you test and make curves, the best advice is to use the speeds you find from your tests. If you have calibrated sensitometer, it will be obvious. If you have a home-made sensitometer that is consistent, but not calibrated... Set the box speed to agree with the curve that "best" fits the ISO parameters where you used a standard developer.

Having done that. Then look at the curve of the film/developer combination you intend to use and use Delta-X criterion to arrive at the EI for that curve.

 

[AndreasT]

Just checking the last graph, the flare also comprsses the contrast of the shadows resulting in worse seperation. By decreasing exposure and expanding development we would improve this.

 

[AndreasT]

OK Bill, of course I have no calibrated sensitometer. I test under my enlarger. You know like it is explained by BTZS. I hope some thing are becoming clear now. BTZS uses the ISO triangle and I always wondered why I was getting more speed than by using the ZS method. Also having problems with flare. Which Stephen explained nicely.
I think I am slowely starting to see the light. Dimly but it is there.
Concerning the Delta-X criterion. Wouldn't it be better to use the full length of the curve (Zone VIII) and mathematically calculate the values we would have at using the ISO triangle.

 

[Bill Burk]

Just checking the last graph, the flare also comprsses the contrast of the shadows resulting in worse seperation. By decreasing exposure and expanding development we would improve this.

You would be better to try to reduce flare. There is reduced separation in the shadows. Fortunately, the reduced separation in shadows is not important to most viewers.

I recently did some graphs where the tests included flare and they didn't fall below 0.1 density.

So you can't reduce exposure and expand development to compensate for flare.

But you can reduce exposure "knowing" that flare will bring up the shadows slightly. Going the other way is OK too. Any increased exposure will look like fogged negatives.

You can decrease the exposure until you feel you are on the toe of the curve. Then you are at the point where you are not making things better.

 

[Bill Burk]

OK Bill, of course I have no calibrated sensitometer. I test under my enlarger. You know like it is explained by BTZS. I hope some thing are becoming clear now. BTZS uses the ISO triangle and I always wondered why I was getting more speed than by using the ZS method. Also having problems with flare. Which Stephen explained nicely.
I think I am slowely starting to see the light. Dimly but it is there.
Concerning the Delta-X criterion. Wouldn't it be better to use the full length of the curve (Zone VIII) and mathematically calculate the values we would have at using the ISO triangle.

What kind of light source do you have on the enlarger?

I do use the ISO triangle to find my speed. Then I stick with that speed.

 

[AndreasT]

Tungsten, but I use a filter, I think it is a 80c. Would have to check that up. To compensate the colour somewhat.

 

[Bill Burk]

Tungsten, but I use a filter, I think it is a 80c. Would have to check that up. To compensate the colour somewhat.

That should be fine.

So you would use the speed you find at the ISO triangle as a benchmark. And if you start to do different developers/compensating developers etc. Then look how the curves compare to find a new EI. Otherwise take that one speed you found in the first place and use it all the time. Delta-X provides the theory that supports the idea that the effective speed doesn't change a lot with changes in development.

 

[Bill Burk]

I find, or at least I believe I've found, that I get a little less than ISO speed from my film. So a little under box speed might be what I am REALLY getting.

 

[AndreasT]

Yes basically looking up my data I get a little under box speed.

 

[AndreasT]

But it gets a bit complicated when we go over to development we have to compenstae for flare. Now this has been discussed here and there. I also PM with some other members. At the moment I am compensating for flare my using a contrast log value of 1,20 instead of the "normal" 1,05. Now Stephen also wrote about this as always I did not follow.
I dare to ask what you Bill, or Stephen thing of this approach.

 

[Bill Burk]

I use a chart Stephen provided that gives Contrast Index to develop to... for the paper grade and subject luminance range.

I start out with 7 stops == N.

The chart has Flare compensation built-in.

And I use the EI based on my speed tests that are basically to the ASA/ISO triangle but I feel are not quite box speed.

I meter using Zone System notation (spot shadow, place on Zone II, or spot skin place on Zone VI etc.)

 

[AndreasT]

I will check up on those charts again tomorrow. I myself use an incident light meter.

 

[Bill Burk]

I will check up on those charts again tomorrow. I myself use an incident light meter.

I often do a sanity check with incident meter. They typically agree. But I would listen to Mark Barendt he uses incident meters / duplex metering...

 

[markbarendt]

My ears are burning. Thanks Bill.

Andreas, the 2/3 stop adjustment to EI that has been talked about here works regardless of meter type. An EI can factor in whatever bias the photographer wants. The ZS simply factors in a preference for more shadow detail than ISO standard.

The real questions are: does it help you get better prints? & what do you have to give up?

 

[Stephen Benskin]

Andreas, the 2/3 stop adjustment to EI that has been talked about here works regardless of meter type. An EI can factor in whatever bias the photographer wants. The ZS simply factors in a preference for more shadow detail than ISO standard.

Yes, but not on purpose. It's not part of the design.

 

[AndreasT]

The real questions are: does it help you get better prints? & what do you have to give up?

Who knows?
It is important for me to know what is going on.
I believe it is important to know the variables to possibly be more flexible in the field. There were a lot of things which I could not answer. Now I know a bit more which of course results in more questions.
It is time to try this out, all the variables and see what results one gets.
The thing with the Delta-X makes perfect sense when actually looking at the curves.

 

[Stephen Benskin]

Michael, I don't believe your theory about the goal of the Zone System has any merit. The EI difference is simply a remnent from before 1960. I guess you could consider that the Zone System didn't have to change with the change in the ASA standard because it was achieving it's goals. You could also consider, it was luck that there was a correlation with the ASA method because of the safety factor in the ASA standard which compensated for the Zone System not incorporating flare. Otherwise an excellent analysis.

 

[Stephen Benskin]

I'm just talking about what people are trying to do when they run ZS EI tests, and what is at stake in terms of image quality etc when one chooses a different EI than the ISO speed. ZS testers are trying to find an effective film speed such that given their processing procedures, when they meter and close down two stops for shadows, they get full separations in the negative. So I don't understand how it is a question of film speed at all. ZS tests are just exposure/development tests to get a desired tonality. Whether or not they get what they think they are getting is another matter.

I've edited the post. My original respnse was based on a quick scan of your post. Sorry about that.

 

[Stephen Benskin]

The luminance range of the standard model is very similar to the Zone System's. In fact, it has 1/3 stop deeper shadows. So instead of the ZS 4 stops, the statistically average luminance range as 4 1/3. According to the Delta-X Criterion, the fractional gradient speed point falls Δ0.29 log-H below the 0.10 density point. This is where the shadow exposure for the standard model would fall in a no flare situation. With flare, the shadows are pushed up to around the 0.10 density point. The ISO standard and Delta-X Criterion use 0.10 density as the speed point. Mostly because it is an easy to find point of measurement, but partly because this is where the shadow exposure will fall. As the ZS has practically the identical luminance range below the metered exposure point, it would go to reason that the shadow exposure will also be brought up to ~0.10 under normal shooting conditions. The ZS test is practically flare free, so the exposure four stops down from the metered exposure point will fall 2/3rd stop below 0.10 density. By increasing the EI 2/3 of a stop, in the no flare testing, exposure then falls at 0.10 density, but with most general purpose developers, if the EI was left at the ISO and an average scene was shot without exposure compensation, flare would bring the shadow exposure up to around 0.10 density.

The example shows just that. The no flare curve's shadow exposure (Zone I) falls at a density of 0.04. With a one stop flare factor, The Zone I exposure falls at a density of 0.12.

 

[AndreasT]

With a lot of my films when I apply the Delta-X (sounds like a secret fighter plane) or the CI ruler my speeds tend to jump about.
Meaning some of my minus curves have more speed than the normal, and the plus curves too. etc..
Now not with all film, or should I rather say not with all developers.
Now some surface developers/compensating developers, or what ever they are technically called have a different spread at the toe region where the curve goes up.
What does one do here, or have I missed something again?
Can this be normal?

 

[Bill Burk]

...If the EI was left at the ISO and an average scene was shot without exposure compensation, flare would bring the shadow exposure up to around 0.10 density.

This is about what I figure as well.

Unless one's development chemistry and processing technique don't reach full potential speed. I forgot to emphasize that in my list of factors. If you don't get full speed, then you shouldn't rate your film at full speed.

 

[markbarendt]

Yes, but not on purpose. It's not part of the design.

If it walks like a duck...

 

[Bill Burk]

We used this thread to establish "why" Zone System speed is often half rated film speed.

But David Allen, in a recent thread, told a story about a student who had 400 personal exposure index for Tri-X when used in the Rolleiflex, but 160 personal exposure index in the Nikon. It wasn't coated lenses that made the difference.

I helped a photographer last year who was seeing personal exposure index of 160 with Delta 100. It was very difficult for me to diagnose. First I thought he was having super-efficient processing in the Nikor 4x5 film tank. But later, seeing his graphs change with a different lens/shutter, it began to be clear that the unusually high speed (would have expected Zone System speed of 50 for Delta 100)... was due to a faulty shutter.

So although people with well-calibrated shutters are seeing half rated speed, it's a fallacy to conclude that the Zone System tests arrive at half rated speed. Because by definition, errors in shutter speeds are included in the personal exposure index.

 

[RobC]

We used this thread to establish "why" Zone System speed is often half rated film speed.

But David Allen, in a recent thread, told a story about a student who had 400 personal exposure index for Tri-X when used in the Rolleiflex, but 160 personal exposure index in the Nikon. It wasn't coated lenses that made the difference.

I helped a photographer last year who was seeing personal exposure index of 160 with Delta 100. It was very difficult for me to diagnose. First I thought he was having super-efficient processing in the Nikor 4x5 film tank. But later, seeing his graphs change with a different lens/shutter, it began to be clear that the unusually high speed (would have expected Zone System speed of 50 for Delta 100)... was due to a faulty shutter.

So although people with well-calibrated shutters are seeing half rated speed, it's a fallacy to conclude that the Zone System tests arrive at half rated speed. Because by definition, errors in shutter speeds are included in the personal exposure index.

+1

As are meter errors which are fine if they are consistently out across the metering range upto 1/2 stop or so but not if they vary across the metering range.