Encouraged by a Zone System workshop last weekend where we could have our negs read by a densitometer, I finally ran a film speed test. It was an abbreviated form where you shoot a sequence of frames trying to find the frame (and E.I.) with a 0.1 density (Zone I). Each frame was offset from the indicated meter reading. The sequence was: -2, -2.5, -3, -3.5, -4, and -4.5 stops from the meter reading. The scene was a medium toned surface uniformly lit by two BCA (blue) 250w photofloods. The meter reading was 1/60 at f/2.8 (8 on the Pentax dial).

Using 35mm Tri-X at ISO 400 developed in D-76 1:1 at 20C for 8 minutes, I got the following results:

-2 stops, 1.40 -2.5 stops, 0.07 -3 stops, 0.03 -3.5 stops, 0.01, effectively blank

This implies that my E.I. for Tri-X is approximately 125. That seems suspiciously low. I used a relatively new Nikon N-80 and a Pentax Digital spotmeter (bought used).

I've repeated the test three times and got similar results where I cross the 0.10 density between -2 and -2.5 stops from the indicated meter reading.

Could you hazard a guess where I went wrong? I'm even more puzzled because rating Tri-X at E.I. 200 yields negs that are very easy to print using my standard print time ("maximum" black, minimum exposure).

I'm at my wits end that I'm going to send my meter to Quality Light Metric just to be sure that it's accurate and linear.

-- Bong Munoz (bong@techie.com), June 21, 2001

Answers

If you get good results shooting at EI 200, I'd say that is what you should use--particularly since it matches most of my own tests with Tri-X. You say it was a medium-toned surface, but that's pretty vague. Was it a grey card? I should note that Phil Davis states that the middle grey of standard 18% grey cards is really a middle grey for reprographic work, whereas the middle grey for general photography falls in the 10% to 12% reflectance range. Most light meters are constructed to give correct readings from 12% grey, which is about 1 stop darker grey than 18%. I suspect that your true EI is 200 to 250.

-- Ed Buffaloe (edb@unblinkingeye.com), June 21, 2001.

My thoughts:

1. Digital Truth says Tri-X at 200 should develop in D76 1:1 for 9.5 minutes, so perhaps a trifle under-developed, which would inhibit speed a little. Is this developing procedure (developer, dilution, time, temperature) your normal? If not, you are changing more than one variable, which makes it hard to pin down.

2. Is your normal 200 rating for blue photo floods or daylight? If your usual lighting is daylight, this might cause the discrepancy. Many people ignore the spectral sensitivity of b&w films, but it can have a real effect. See: http://www.kodak.com/global/en/professional/support/techPubs/f9/f002_0 360ac.gif

3. My Pentax digital spotmeter (Zone VI modified) consistently gives tests that are about 1/3 stop faster than ISO ratings. I suspect my shutters are just slow. If your meter is, however, consistent (it sounds like it is, since you repeated the tests with similar results) I wouldn't bother to send it out for repair.

4. In any case, if your spotmeter gives you consistent results with negatives that you like using 200, then use 200. Photography is about results, not testing.

5. A film-base-plus-fog density of 0.01 is too low for Tri-X 35mm, so something seems amiss in your density readings. Perhaps FBF has already been subtracted? FBF for Tri-X 35mm runs around 0.18 to 0.25 if I remember right.

By the way, your "-2 stops etc." discussion doesn't seem quite right. Two stops under exposure (and I gather that -2 means closing down 2 stops), means the speed would be rated at 1600. You can figure out if you said what you meant, and my comments are based on the other info you provided.

-- Charlie Strack (charlie_strack@sti.com), June 21, 2001.

Ed, I thought that it did not make a great difference what tone my subject is. If theory matched practice, a gray card placed at Zone I would yield a negative at 0.1 density and a white wall placed at Zone I would also yield a negative at 0.1 density. I thinking of the proverbial gray snow or black dog, white dog thought experiments.

In this particular case, I used a gray card, a medium blue poster board, and a dark maroon wool blanket all lighted identically. Of course only the gray card read 1/60 at f/2.8.

I don't really mind rating Tri-X at 200 since I've gotten good results so far. However, I'm anal enough to be bothered that I'm nowhere near the expected theoretical result. Is it possible that "normal" 35mm negs are really supposed to be thinner than 4x5?

-- Bong Munoz (bong@techie.com), June 21, 2001.

Charlie, I have to admit that my normal development time used to be 10 minutes. I used 8 minutes because that was what our test procedure recommended. I will repeat the test tonight and go back to my 10 minute regime.

My normal rating of 200 is for daylight. However, I also exposed a few frames of normal scenes (contrast range of 5 stops) using the blue photofloods and those printed easily at my usual standard printing time.

The density readings are net density. The fb+f density has been subtracted.

The test procedure is meant to find the E.I. that yields a Zone I negative with a 0.1 density. This means if frame 1 is Zone I (-2 stops under) then my E.I. is 100. If it's frame 3 (-3 stops under) then my E.I. is 200. If it's frame 5 (-4 stops under) then my E.I. is 400.

My thanks to you and Ed (and to others, in anticipation) for taking the time to think about this. I'll try to return the favor by putting up my results with explanations when (and if) I get to the bottom of this.

-- Bong Munoz (bong@techie.com), June 21, 2001.

Bong: Just so there's no misunderstanding, although what you're doing may be correct, how you're describing it is not. It's not that you are supposed to look for the negative "with a 0.1 density (Zone I)". Instead, you're looking for the exposure that will produce a .08 to .12 density OVER FILM BASE PLUS FOG! Your description would not work with many films because their base density and fog is ABOVE 0.1. Assuming you did it correctly, despite your description, then that might indeed be your film speed WITH YOUR CAMERA, METER, DEVELOPER and PROCEDURE. All you are looking for is consistency, not a specific number. Just what is right for you.

Have you proceeded with the next step: determining your correct negative development time? Believe me, the two are NOT necessarily the same. Rather than fill this with the details, I suggest you find a copy of Fred Picker's "Zone VI Workshop" which provides the instructions. Normally the first test should reasonably define your film speed, but occasionally, it might be off a bit. The proper development time will produce a negative that, when exposed for Zone VIII at the tested ASA rating, achieves a density that will produce a print value of VIII on YOUR printing paper. It's not easy. But when you find it, you've got it - forever! Then you can get on with what's important - taking real pictures. Good luck.

-- Alec (alecj@bellsouth.net), June 21, 2001.

Are you sure about the Zone I density? it should be around .10 not 01. Development time is going to effect the middle and higher values not the low end. If you are happy with the negatives you have been getting with detail in the shadows stay with it.

-- ann clancy (clancya@mediaone.net), June 21, 2001.

One more thing. Your setup was not correct. You indicated you had three targets, all in the same light. Wont' work! If you did it that way, you sure didn't measure a complete range of light between Zone I and Zone IX. The only way to do that is put the Zone I subject [preferably dark] in the shade, and the Zone IX subject [preferably white] out in bright light. If you are honest with yourself, that's the only way to get that range of measurements. In the same light, your "black horse, white horse" might work because they aren't normally at the extreme end of the exposure scale, but true Zone I and Zone IX subjects will NEVER meter correctly in that light. It's true. GO DO IT, don't just talk about it.

-- Alec (alecj@bellsouth.net), June 21, 2001.

First of all, my apologies for typing 0.1 instead of 1.0 as the density I'm shooting for. Thanks, Ann. Now...

Alec, I should've emphasized that the densitometer readings were NET density. The film base + fog density has been subtracted.

I haven't moved forward with my N-, N, and N+ times yet because I'm not confident that I've found my EI for Tri-X. I'm aware of the full calibration process. I've a fair library of references on the Zone System from Adams, Barnbaum, Bond, Davis, Graves, Johnson, and White. Not Picker .

Could you explain why my setup is wrong? This was the recommended setup in the workshop I just attended. I realize it's an abbreviated form of the full ZS calibration procedure but if the intention is to find the EI where Zone I yields a negative with a 0.8 to 1.2 NET density then it looks correct. Why would I need a full contrast range to do this?

If I sound like I'm engrossed in testing than taking pictures then, yes, at this point in time I am. I'm currently fascinated by the sensitometric part of photography even if my controls are slightly loose. The small amount of information that I've uncovered so far has infused the "art" portion of my photography with more confidence so it's not all for naught :)

-- Bong Munoz (bong@techie.com), June 21, 2001.

Hi Bong, Just a minute question: which is the transmission factor of the lens tested? If it's a zoom lens, a hand-held photometer can't be taken for granted unless some sort of compensation is computed for many glass elements. In-camera meter should mark this difference. Regards,

Cesar B.

-- Cesar Barreto (cesarb@infolink.com.br), June 21, 2001.

Cesar, I used a 50mm f/1.8 lens set to infinity. The camera was on a tripod and the uniformly lit surface filled the viewfinder. I used a separate meter, a Pentax Digital Spotmeter, because this is the meter I intend to use for zone work. Zone work, 35mm, hmmm...

-- Bong Munoz (bong@techie.com), June 21, 2001.

I just did this same test and discovered it's very easy to make mistakes! I left the camera on auto so it adjusted the shutter as I adjusted the aperture! Doh! Anyway, Zone 1 should be 4 stops down from Zone V. I'd change the E.I. in 1/3 stop increments to find .1 over B+F. The aperture is too coarse. Development won't affect it much. Use any gray or white target, since the meter will try to put it at Zone V. Be sure the target area is large enough on the film, as most densitometers have a several mm diameter reading aperture. Unless all your work is under floods, do the test in daylight. Meters don't have flat spectral response, nor does film, and it may make a significant difference in the result. The general opinion seems to be that Tri-X is in the 200 region, so your results aren't that strange.

-- Conrad Hoffman (choffman@rpa.net), June 21, 2001.

Bong not be beat a dead horse but I sense you really want to get this test down pat. when you talk about 1.0 being Zone I , that density -fb+fog is going to be pushing you up to the Zone VII range, somewhere between VI and VII. I have had students run this test many times and it is easy to go crazy over something which one would think is simple. One tip i suggest is to vocally say out loud what Zone you are shooting as you stop down or up . Helps keep one on track. Also, try not to change a shutter speed when you get to the point when you are ready to test for development time. At that point I also recommend to my students that they a frame at each Zone so when they are read you can confirm that a mistake hasn't occurred. there is a logical progression from Zone I- ZoneIII and then from Zone IV up to VIII. At VIII don't forget to test for paper type and light source. Have fun and enjoy playing with the more technical end of our craft. When you are ready to transfer the technical information to the artistic side of the fence I am sure your prints will be much improved. Also, don't forget different develpers and film types may tested diffently, don't assum that a film rated at 400 and test for 200, means that all film needs to be shot at half the rated speed. As a rule of thumb I suggest to my beginers that they should try that and see if they like the results. My serious work needs personnel testing.

-- Ann Clancy (clancya@mediaone.net), June 21, 2001.

When I referred to your setup, I was reading your statement: "In this particular case, I used a gray card, a medium blue poster board, and a dark maroon wool blanket all lighted identically. Of course only the gray card read 1/60 at f/2.8.". There's no reason to use anything but the dark blanket since that's the only thing that will be measured. It appeared to me you had used this setup thinking you were covering the whole spectrum from Zones I to IX and I suggested that couldn't happen.

Obviously you are headed in the right direction since you say your negs are getting better. Isn't that all you are interested in? It doesn't matter if the number is 100 or 500, if everything is done consistent and the results are repeatable. My TX35 number is 200, w/HC 110, and others have agreed you are in the general "ballpark".

Check your math again. The correct reading is .08 to .12 over film base plus fog. NOT 1.0. Use normal shutter speeds, e.g. 125. How did you get to 1/60th. If you started at 1/125 and f/16, and then reduced your steps by half stops, you should have gotten to 200, or even 100 long before you had to reduce your shutter speed. That's just another variable in your equation - the shutter speed might be off somewhat. It doesn't matter - if that is the shutter speed you will most always use! And remember, Zone I is not minimum density: Zone 0 is. There's only a minute difference [hence the .1 figure] between the two. You are using manual settings, aren't you? This is a manual test - don't let the camera do ANYTHING automatically.

-- Alec (alecj@bellsouth.net), June 21, 2001.

Sigh, I always confuse the density values. I'm looking at my workshop notes and on the graph I have net density values from 0.01 to 0.14. I apologize for the order of magnitude mistakes in my earlier posts.

I'm not doing a good job describing how I carried out the test. I really wish I made the simple mistakes you all mentioned like forgetting that I'm on shutter priority mode, for example.

Conrad, I'd like to use 1/3rd stops but my Nikon only has detents at 1/2 stops. I believe these electronic shutters are actually stepless in idiot mode -- I wish the camera manufacturers would let us choose shutter speeds in 1/10 stops in manual mode :)

Ann, what peeves me is that the test *is* really simple. I have a checklist that I run through forwards and backwards before shooting the first frame. I make sure to use the same film, developer, and thermometer. Perhaps what peeves me is that almost everything is a variable. What if the densitometer was off? What if my shutter is off? What if my meter is off? What if my thermometer is off? Do I have to get 0.1 net density? How far off, more or less, can I deviate from this bar? Now I have to make do using my lightmeter as a crude densitometer. Oh, joy!

Well, I'll let this particular horse lie now. I appreciate and am thankful for everyone's indulgence. I really am dense, Alec, I'm not even trying . I'll do a few more runs before admitting defeat, taking 200 as my EI and proceeding with my N-, N, and N+ tests. I'll let you know how this particular story ends. Thanks again!

-- Bong Munoz (bong@techie.com), June 21, 2001.

First of all, you haven't calibrated anything to anything.

It's pretty well-known that light meter manufacturers don't agree on a standard and there is no real standard...so you have to come up with your own.

The 18% grey card is a pretty handy and relatively standard reflection target; the Wallace Expo-Disc is a handy 18% transmission target.

Assuming you're not living in the far north or the tropics, "Sunny f16" should be valid. That is, when metering a grey card or Expo-Disc in full direct sunshine the light meter should read 1/EI @f16. Arbitrarily pick an EI, say 125, and set that on the meter, set the lens at f16, read the target and the recommended shutter speed should be the same as the EI, in this case, 1/125.

If it is, you're done. If not, adjust the meter's EI setting until it reads 1/125 @f16. How many thirds of a stop you have to set the meter EI to get that reading from what it should be will be the correction factor for that meter.

For example, if you have to set the meter EI at 80 to get 1/125 @f16, what you've learned is that you need to set the meter EI 2/3 stop lower for _all_ EIs with that meter.

Chances are you'll have different correction factors for each meter.

Once you've gotten that squared away, you can proceed.

The traditional minimum Zone I density is .10 DU above fb&f. This isn't engraved in stone; if you find that you want more or less shadow detail adjust that target accordingly.

Now you're ready to test. Light bulbs put out lots of IR and meters are sensitive to IR out of proportion to the visible light the bulbs put out, so do this outdoors. Set up so that the meter sees only the target (grey card or Expo-Disc) and set the aperture to f2.8, then set the shutter speed to whatever's indicated. Stop down three stops, which would be the anticipated Zone II, and shoot a series of exposures while stopping down two stops. Ideal would be decreasing exposures in 1/3 stop intervals but that's just about impossible to do if your camera doesn't have click-stops in 1/3 stop intervals. The reason for starting out at f2.8 is so that the shutter speed will be high enough that reciprocity failure isn't a factor.

Develop the negs and read 'em with the densitometer. With luck your Zone I exposure will be .10 DU above fb&f. If not, if for example you don't see .10 DU until Zone II, then you know that with your equipment your working EI for the film is a stop lower than whatever you used for the test.

For TX developed in "normal" developers I'd expect to see EI 200 to EI 400; too far off from that range would send me looking for an error.

-- John Hicks (jbh@magicnet.net), June 21, 2001.

I also recommend Fred Picker's book. He describes the tests so clearly that the price of the book is worth it for this alone.

Repeat the tests using daylight--that will take the color sensitivity out of the equations. These spot meters are affected by infra-red light, which could be the contributing factor.

-- Charlie Strack (charlie _strack@sti.com), June 21, 2001.

John, how should I angle the gray card in sunlight? I've gone through the archives on photo.net but I haven't read a concensus. You seem to have been through this meter calibration before so I'd like to hear and try what you say.

Charlie, I will consider Mr. Picker's book. I've heard less than glowing feedback concerning his understanding of the Zone System but I will try to keep an open mind when I read his book. Your comment about the amount of IR present seems to echo what I'm just now reading in Henry's "Controls in Black & White Photography".

-- Bong Munoz (bong@techie.com), June 21, 2001.

Bong As long as you are using the same tools and nothing changes it doesn't make a difference. A number is just a number. It is the results that count. I had a student once, a young high school kid who had to shoot at an EI of 900 and the development time was way out there (I don't remember)had great negatives. He had a problem camera and no money to repair. we just figured out what he needed to do to get proper results. Take a breath, use the same equipment, keep time and temperature constant , and if the prints are great don't get caught up in a number

-- ann clancy (aclancy@broadband.att.com), June 22, 2001.

Reading the density of uniform negative won't always give an accurate EI unless all you take are photos of uniform gray objects. All lenses have some haze which reduces contrast, then there's flare and internal lens and body reflections, all affecting the shadows most. Try taking a photo of a black object (like a card covered with black felt) under the conditions you want to use the EI in a "normal" scene. The image of the object on the neg must of course be larger than the aperture of the densitometer.

-- Tim Brown (brownt@flash.net), June 22, 2001.

> how should I angle the gray card in sunlight?

Good question. The reason the angle is important is that the "standard" is about 13%, not 18%.

Kodak used to state that the grey card should be held vertically, taking care not let it shade itself or hold it at an angle that produces glare, and hold it at a 45-degree angle to the light source. The reason was that this would produce around 13% reflectance, even though the card was 18% reflectance.

This vanished from the grey card instruction sheet a decade or so ago.

After a recent debate about 13% vs 18%, Bob Shell contacted someone at Kodak regarding the change in instructions. It turned out that when Kodak revised the packaging for the grey card, someone _forgot_ to include the instructions about how to hold the card at the proper angle!

I believe that's back in the instruction sheet, but since I haven't bought or looked at it I don't know.

Anyway...the _correct_ method is to hold the card vertically and turn it to about a 45-degree angle. Which is very difficult to do consistently.

The difference in how you hold the card results in about a 1/3 stop change; that much error isn't desirable but otoh isn't huge either.

I avoid the problem entirely by simply using 18%. After all, if my meters get set 1/3 stop higher or lower than someone else's it makes no difference at all. Actually to eliminate the vagaries of using a grey card a Wallace ExpoDisc (www.expodisc.com) works great.

Over the years I've found that my EIs resulting from calibrating with the 18% ExpoDisc have usually agreed with others not using exotic developers within 1/3 stop, sort of a reality check.

-- John Hicks (jbh@magicnet.net), June 22, 2001.