Making a Zone Ruler

[Bill Burk]

An idea that I had based on some discussions here, was that it's not easy to find a clearly printed example of Zone System patches from Zone 0 through Zone X.

There are plenty of books with lithographically-printed explanations and illustrations, but these are not Silver Gelatin prints.

I felt a great leap in confidence when I put a "Zone Sticker" on my Master II light meter that I cut from pieces of an actual print. I thought it might be useful, generally, to have a concrete example of Zone 0 through Zone X, as they appear on print.

So I set out to make a Zone Ruler.

Maybe the steps will be easy enough that anyone can make their own. I have a calculator with Log functions that helps me work quickly with these figures... And I take a commonly held assumption for flare: 0.40 log units exposure added overall at the film plane.

I start with a step wedge, and I use it to expose a test strip on film. Then I develop that film normally. In my case I had plenty of test negatives to work with so I chose a step wedge negative that was developed to 0.58 Contrast Index (CI).

I "masked" the the negative with black paper tape to cover up much of the clear areas, so that I don't overwhelm the print with flare.

Then I put the negative in my enlarger, at the usual height for making prints, and exposed a print.

This print is a step wedge, but it's not a first-generation step wedge. Instead it's a print that includes the film characteristics and the paper characteristics. It almost reflects the whole Tone Reproduction Cycle (except it leaves out flare).

So, let's say I have this print. It has 21 steps, 0.15 exposure units apart on the negative but not necessarily that same spacing on the print.

Flare hasn't been factored in.

But let's assume Zone I was "supposed" to be 0.1 on the film. I can go back to the characteristic curve of the film and find that point on the negative.

Since the film was ISO 400, developed to nearly the ASA gradient, I can consider the 0.10 speed point as -2.7 Log meter candle seconds. For the next steps it helps to convert to arithmetic units: So it's 0.002 meter candle seconds. I'll add 0.40 log units exposure for flare. -2.7 + .4 = -2.3 which is 0.005 meter candle seconds. The difference is what is added by flare over the entire image plane: 0.003 meter candle seconds.

I printed the negative to get paper black on Step 1. Step 2 hit 0.10 on my example negative - that makes it easy. Step 5 is the step 0.4 log units to the right... So considering flare, my first patch of the Zone ruler... Zone I, will be a cutout from Step 5.

Which will be the second patch? It will be based on the step 0.3 units to the right of Step 2. Step 4... -2.46 log mcs. To arithmetic: 0.0035 mcs. Plus 0.003 again is .0065 mcs. -2.18 log... This is step 6.

Third patch? based on the step 0.3 units to the right of step 4. Step 6. -2.18, we know is .0065 mcs plus .003 is .0095 mcs. -2.02 log mcs. This is Step 7.

Fourth patch? based on step 0.3 units to the right of Step 6, Step 8. -1.88 is 0.013 mcs. Plus .003 is .016 mcs or -1.79 log mcs and that is right between Step 8 and Step 9. Now I have to cut out from one or the other. I'll just take Step 9 and see where it takes me from here.

Fifth patch? based on step 0.3 units to the right of Step 8. Step 10. -1.58 or 0.0263 plus 0.003 is .00293 or -1.53 log mcs Right between Steps 10 and 11. See the pattern. We've gotten down to where the flare doesn't matter anymore and each new patch is two steps to the right.

So we'll take the odd Steps from here on out... Steps 11, 13, 15, 17, 19 and 21 to finish the series.

So the finished ruler will come from cutout samples of steps:

5, 6, 7, 9, 11, 13, 15, 17, 19 and 21.

Will there be a Zone 0? No. Or if so, it would also come from Step 5 because there isn't any way you can get a lower exposure on that film plane than the amount that was added by flare.

In my paper print, step 18 was the last faint tone before paper white, so Zones IX and X will be paper white on my Zone ruler.

 

[Bill Burk]

...But let's assume Zone I was "supposed" to be 0.1 on the film. I can go back to the characteristic curve of the film and find that point on the negative.

Since the film was ISO 400, developed to nearly the ASA gradient, I can consider the 0.10 speed point as -2.7 Log meter candle seconds. For the next steps it helps to convert to arithmetic units: So it's 0.002 meter candle seconds. I'll add 0.40 log units exposure for flare. -2.7 + .4 = -2.3 which is 0.005 meter candle seconds. The difference is what is added by flare over the entire image plane: 0.003 meter candle seconds.

I printed the negative to get paper black on Step 1. Step 2 hit 0.10 on my example negative - that makes it easy. Step 5 is the step 0.4 log units to the right... So considering flare, my first patch of the Zone ruler... Zone I, will be a cutout from Step 5.

...

Will there be a Zone 0? No. Or if so, it would also come from Step 5 because there isn't any way you can get a lower exposure on that film plane than the amount that was added by flare.

Well actually there is a lower amount of light than the step for Zone I. The step for Zone 0 would be "Just" the flare light. 0.003 meter candle seconds. -2.52 log mcs. From my film's characteristic curve I know that much light will cause a density of 0.18 which is close to Step 3.

So starting with Zone 0, the finished ruler will come from cutout samples of steps:

3, 5, 6, 7, 9, 11, 13, 15, 17, 19 and 21.

An interesting thing to see is that step 3 is close to the 90% DMax of the paper for Grade 2 print from 0.58 CI negative.

It's interesting to see that a lot happens between Zone VII and VIII, the step in-between is clearly visible but the VIII patch is barely there.

 

[gzinsel]

Im a little behind the curve so to speak. so be patient with me . . . "you zoners" . can you please clarify .58 CI for me? I am confused?? when I take density reading of zone III, I am getting somewhere around.12-.13. . . . on my densimeter, my base+fog is .04 clear film no exposure, but developed,fixed, etc. . My highlights ( zone VIII) is around 1.25 or so. . . if I subtract them , I would get the Contrast Index??? or am i doing it wrong?

 

[gzinsel]

my bad, I meant zone I is .13 not zone III

 

[Stephen Benskin]

Im a little behind the curve so to speak. so be patient with me . . . "you zoners" . can you please clarify .58 CI for me? I am confused?? when I take density reading of zone III, I am getting somewhere around.12-.13. . . . on my densimeter, my base+fog is .04 clear film no exposure, but developed,fixed, etc. . My highlights ( zone VIII) is around 1.25 or so. . . if I subtract them , I would get the Contrast Index??? or am i doing it wrong?

Contrast Index is a form of average gradient (Rise/Run). The average gradient of your test negative would be 1.12 / 2.1 = 0.53. Bill is expressing the contrast to which the film was developed.

 

[gzinsel]

thanks, I get it, now.

 

[Bill Burk]

I started double-checking my steps on the negative and the steps on the print and while re-drawing the film curve I realized that my "Steps" are numbered wrong. Nothing wrong with all the math so far. But my new sequence of Steps is what I said earlier "minus 2 steps".

So the sequence will go:


1, 3, 4, 5, 7, 9, 11, 13, 15, 17 and 19.

Zone 0 = Step 1
Zone I = Step 3
Zone II = Step 4
Zone III = Step 5
Zone IV = Step 7
Zone V = Step 9
Zone VI = Step 11
Zone VII = Step 13
Zone VIII = Step 15
Zone IX = Step 17
Zone X = Step 19

This throws out my interesting earlier observations about the shadows and highlights.

Right now it appears: Zone IX falls on the 0.04 paper and Zone X is paper white. Zone III falls on 90% DMax and Zone 0 is DMax.

 

[Bill Burk]

I kept saying 0.58 CI but the negative was really 0.57 CI (trivial difference).

Here is what the test negative looks like (the negative I put in the enlarger to make the Zone Ruler).

The strip on the left-hand side is the one we focused our attention on. The one on the right-hand side that looks like it was divided in two was done with an ND filter so that I could reach deeper into the toe for the film graph. But I will be using the complete strip on the left-hand side for the Zone Ruler.

0.57 CI Test Negative

 

[Bill Burk]

Here is the graph of the test negative with Steps identified and the planned corresponding Print Zones.

0.57 CI Test Negative Film Characteristic Curve

 

[Bill Burk]

Here's the graph of the Zone Ruler print

Zone Ruler Print Graph

 

[Bill Burk]

Here's the Zone Ruler raw print.

Zone Ruler raw print

 

[Bill Burk]

Here's the Zones marked out on the Print.

Labeled Zone Ruler Print

 

[Stephen Benskin]

Nice. These help. Thanks Bill.

 

[Bill Burk]

After repeating the math, with the mistakes corrected...

Since the film was ISO 400, developed to nearly the ASA gradient, I can consider the 0.10 speed point as -2.7 Log meter candle seconds. For the next steps it helps to convert to arithmetic units: So it's 0.002 meter candle seconds. I'll add 0.40 log units exposure for flare. -2.7 + .4 = -2.3 which is 0.005 meter candle seconds. The difference is what is added by flare over the entire image plane: 0.003 meter candle seconds.

So far so good

I printed the negative to get paper black below Step 1.

0.10 density was reached on a step under an ND filter on the right-hand side of the negative (the side that we aren't working with) but flare is going to raise that to a step that we can take from our main strip on the left.

So we'll continue...

Looking at the graph of film Step 3 is the step 0.4 log units to the right of Zone I, at the 0.10 speed point on the original negative.

I'll say that including flare, Step 3 = Zone I.

Which will be the second patch? It will be based on the step 0.3 units to the right of where Zone I was before flare, then we'll add flare.

Step 2 is there. Step 2 is -2.38 log mcs. To an arithmetic number: 0.0042 mcs. Plus 0.003 again is -2.14 log. This is really close to Step 4. (Step 4 is -2.12).

I'll say that including flare, Step 4 = Zone II.

Third patch? based on the step 0.3 units to the right of where Zone II was originally placed: Step 4. Step 4 is -2.12 log mcs, 0.0076 mcs plus .003 is .0106 mcs. -1.97 log mcs. This is really close to Step 5.

I'll say that including flare, Step 5 = Zone III.

Fourth patch? based on step 0.3 units to the right of where Zone III was originally placed: Step 6. Step 6 is -1.82 log mcs, which is 0.015 mcs. Plus .003 is .0018 mcs or -1.74 log mcs and that is right between Step 6 and Step 7. Now I have to cut out from one or the other. I'll just take Step 7 and see where it takes me from here.

I'll say that including flare, Step 7 = Zone IV.

Fifth patch? based on step 0.3 units to the right of where Zone IV was originally placed: Step 8. -1.53 or 0.03 plus 0.003 is .033 or -1.48 log mcs. Between Step 8 and 9. See the pattern. We've gotten down to where the flare doesn't matter anymore and each new patch is two steps to the right.

I'll say that including flare, Step 9 = Zone V.

So we'll take the odd Steps from here on out... Steps 9, 11, 13, 15, 17, 19 to finish the series.

Zone 0 still can be assumed to have 0.003 exposure (nothing plus flare)

So the finished ruler will come from cutout samples of steps:

1, 3, 4, 5, 6, 7, 9, 11, 13, 15, 17, 19

 

[Bill Burk]

Fifth patch? based on step 0.3 units to the right of where Zone IV was originally placed: Step 8. -1.53 or 0.03 plus 0.003 is .033 or -1.48 log mcs. Between Step 8 and 9. See the pattern. We've gotten down to where the flare doesn't matter anymore and each new patch is two steps to the right.

Actually it looks like I should take Step 8 here instead of 9. It's not "between" it's something that's better rounded to 8. And it's better to use the even series from 8 instead of the odd series from 9

But I've already drawn all the graphs with the odd series. So we have messy graphs that show my thoughts that I believed was correct an hour ago.

Also 0.003 flare for Zone 0 isn't exactly right either. Zone 0 would start with .001 mcs + .003 mcs = -2.4 log mcs so it's closer to Step 2.

So to sum the steps for the Zone Ruler then,

I should use

Zone 0 = Step 2
Zone I = Step 3
Zone II = Step 4
Zone III = Step 5
Zone IV = Step 7
Zone V = Step 8
Zone VI = Step 10
Zone VII = Step 12
Zone VIII = Step 14
Zone IX = Step 16
Zone X = Step 18

 

[Bill Burk]

Here's the latest correction, Zones marked out on the Print.

Labeled Zone Ruler Print v2

 

[Stephen Benskin]

Bill, should there be a bigger gap between III and IV then between IV and V?

 

[Bill Burk]

I've reworked everything today and will show the new results shortly.

Flare and the strong shoulder of the paper curve compresses everything in the shadows so that Zones 0, I, II and III are sequential from Steps 20, 19, 18 and 17. In my opinion, while the camera plan had seen 1 stop between each shadow zone, flare compressed the tones in the shadow so much that they are effectively a half-stop apart for the bottom four zones. The shadows are very compressed, there is little detail in the shadows. Note that film toe also contributes to the compression in the shadows but not nearly as much as the paper shoulder, (note, this is for TMY-2 which has a short toe).

I think that kind of behavior in the shadows is commonly understood. This exercise drove that point home for me.

Then for Zone IV, Zone V, Zone VI, Zone VI and Zone VII every other Step represents a Zone. That's as you would expect.

For Zone IX and Zone X the toe of the paper compresses tones again, there is so little separation that you really do need to be careful holding tones around Zone IX. They are fragile.

Though I computed a skip step for Zone X as Step 3, I didn't need to skip the step because the step right next to Zone IX, Step 4, is already paper white. This gives me a ruler made out of 7 print chips: Zones 0, I, II, III in one piece, Zone IV, V, VI, VII and VIII in individual pieces and the last piece has Zones IX and X.

I've made 5 Zone Rulers according to this plan, since I'm pretty sure I got it right this time.

 

[Bill Burk]

Film Graph - Final Version

 

[Bill Burk]

Print Graph - Final Version

 

[Bill Burk]

Raw Print - Marked (and has been Cut for Rulers)

 

[Bill Burk]

Here are 5 finished Zone Rulers.

They are shown next to a standard Stouffer Cameraman's Grayscale because they differ significantly.

While the Stouffer scale shows half stop steps in terms of reflectance...

The Zone Ruler shows how a metered Zone will appear on a finished print.

Mostly because of the S-Curve of paper, the prints that you get from any negative will not be stepped in the same way as a grayscale. There is compression in the shadows, and compression in the highlights. The Zone Ruler shows the compression that happens, so it helps you see...

When you place something on a Zone, what it might look like on a print.

Finished Zone Rulers

 

[Bill Burk]

The pictures are the pretty part.

Here's the ugly part...

My previous negative graph was on old graph paper, and on that old paper I had a different estimate of how many meter candle seconds the EG&G sensitometer puts at the film plane. So I got out the current graph paper and all the "actual" exposure numbers had to be changed. But this didn't change the overall story. It just changed some facts.

(This is why it is important to know the amount of light that a sensitometer puts out: If I knew exactly how much light my sensitometer put out, I would have a graph paper that doesn't change every time I go to interpret a test result. But... I know what I've got. Sometimes I have to change things after my first drafts as I get a clearer picture of what's going on. Sure would be better with a better sensitometer. You go Michael R 1974. I am rooting for you to invent a good simple reference sensitometer.)

I have some explaining to do how I got from the graphs to the rulers...

 

[Stephen Benskin]

Print Graph - Final Version

Okay, I see what you've done. This is the print from the test negative. It took a minute to realize I wasn't looking at the paper curve. You're next step should be to plot the Zone densities on the paper curve.

 

[Bill Burk]

Zone Ruler plan:

Zone I is at film 0.10 speed point at -2.43 log meter candle seconds (mcs) is 0.0037 mcs

This corresponds to a little above the speed of 200 for TMY-2. Although the film has a rated speed of 400, this negative was developed to 0.57 CI and is below the ASA requirements. So it makes sense that the Exposure Index for this negative is 200.

Speed point exposure, plus the assumed 0.4 flare assumed to be there at that point.
Zone I = -2.43 log mcs + 0.4 flare = -2.03 log mcs = 0.0093 mcs

0.0093 mcs (exposure with flare at speed point) - 0.0037 (planned exposure at speed point) = 0.0056 mcs flare at camera film plane.

Flare 0.0056 meter candle seconds... Gets used a lot in these examples because that's the overall flare light, so every Zone gets that much additional exposure above what you planned to give... In the higher Zones it doesn't matter that much so after a few Zones we can stop calculating it.

Zone I on the bottom scale shows planned 3.08 moved -.4 to 2.68 with flare (The bottom scale is a step wedge on the film plane, so on the bottom scale numbers go down as less gets in the way of the light making it brighter. The top scale is Log MCS and they are negative log numbers because they are small numbers that become less negative as you get brighter.)

Zone I with flare, Print Reflection Density is 1.76

Step 19 Print Reflection Density is 1.74. Good enough.

Zone I = Step 19