Zone V exposure

Sorry for such a simple and naive question but here goes. If I meter a uniform

surface does the meter "assume" that this is zone V?

 

A related question: Dos zone V correspond to an assumed 18% reflection or some

other value?

 

Thanks.

 

Alan

Try this, for starters:

 

http://en.wikipedia.org/wiki/Zone_system

Alan,

your meter will assume that everything is 18% grey. So if you point the meter at something black, it will read it as grey. Same thing happens if you point it at something white.

 

So, if you point the meter at something black, and you want it to appear as black, stop down 2 stops. If you point the meter at something white, and you want it to be white, open up 2 stops.

 

The best and easiest book that I have read about the zone system is called the Practical Zone System by Chris Johnson.

 

Good luck.

 

Good luck.

To elaborate, I have been reading a lot about the zone system, and most of it says that the meter reading is calibrated for zone V, and that this corresponds to 18% reflection. Also assumed is that 18% represents average reflectance. However, I have also read a number of challenges to those assumptions, and I am therefore somewhat uncertain of the facts.

 

Also, related to this, I have read that zone I is considered, on the negative, to be 0.1 log density units higher than base plus fog, and zone V would be four stops higher. One thing that is a little troubling about this is that I have a densitometer, and I have been doing some film/developer testing. So far I have tested three films and three developers (though not in all combinations yet) and in no case does the speed point (zone I) come close to the rated speed, generally running 1-2 stops low, so I am starting to wonder if I am doing something wrong.

Thanks for the clarification.

 

Your description of Zone I sounds like the standard one; it agrees with Fred Picker's Zone VI Workshop, as an example. But if you're finding that your "personal film speed" (as Fred puts it) is a stop or so slower than what the manufacturer wrote on the box --- well, that's not at all unusual, methinks.

Personal film speed also depends on what developer you are using.

What is your question?

 

1. The meter will assume everything is Zone V (as stated by others).

 

2. People have argued that 18% is wrong, it should be 13%. But I don't see what the actual % matters. I'm no academic, I just want Zone V when I print.

 

3. If your Zone I doesn't read 0.1, then it could be the exposure or the printing, assuming the meter is calibrated correctly. Which one is the cause may take you some time to find out.

 

4. Most film manufacturers are optimistic in their ISO ratings. Meaning, the real film speed is probably slower.

"One thing that is a little troubling about this is that I have a densitometer, and I have been doing some film/developer testing. So far I have tested three films and three developers (though not in all combinations yet) and in no case does the speed point (zone I) come close to the rated speed, generally running 1-2 stops low, so I am starting to wonder if I am doing something wrong."

 

Maybe, maybe not. Are your readings consistent from camera to camera? If so, maybe your thermometer reads high or maybe you need to agitate more frequently when developing your film. Maybe you start out with the right temperature, but it cools off a lot during the development cycle. Maybe your developer is weak. Maybe the develope you are using doesn't deliver full film speed. Who knows? Lots of variables can cause a lower than expected film speed. If it's only apparent with films exposed in one camera, any of the above can still be the case, but now you can add in that the shutter might be running fast or that the iris is mis-calibrated.

 

There is no easy answer to this one. Think about how many variables must all be right on the money for things to work out exactly as planned. Any one of them out of spec could account for anomalous readings.

"Personal film speed also depends on what developer you are using."

 

Hi David,

 

Can you explain this as I was told that choice of developer was not important when working out your personal film speed. I think Fred Picker also said this.

 

Peter

Lower densities are less influenced by development than by exposure. Consider the development curves which compare various development times. The toe (thinner densities) hardly changes with increased development.

This is why speed is determined at the lower densities.

Most film is speed rated at a point of 0.3 above base plus fog. You would have to massivly over develop the film to get a + 1 stop increase in density at this point.

Look to your exposure/ meetering to determine why your lower densities are higher than expected.

Yes exposure meeters assume that the world averages 18% reflectance (except Nikons which think the world is 36%)

Kim Kolakowski

Hi Alan,

 

The answer to both questions is yes, assuming that exposure and development are correct.

 

Especially in the case of 35mm, you need to understand that these films don't have anti-halation backing, it would be too thick, therefore the film base is died a neutral grey averaging about .20 (2/3rds of an f stop), in addition, film fog levels may increase the film base plus fog to even more approaching a neutral density of 1 f stop. Therefore, when doing sensitometry, it is important to use "net density" with the FB+F subtracted from the reading. Roll and sheet films have much lower FB+F levels but should be considered.

 

Traditionally, Zone 5 net density should be .70 +/- .05 (the reflection density of a neutral grey card is .70).

 

Lynn

I found some more information that can account for at least part of film speed discrepancy discussed above.

 

There is and article called "Exposure Metering" by Jeff Conrad. According to Mr. Conrad the speed point of a film determined by a typical Zone System calibration (four stops below the metering point, which is assumed to be at zone V) is approximately one half stop slower than the analogous ISO definition.

 

This actually gets me pretty close to box speed for a Tri-X test (T-Max developer, 1+5 dilution, 75 C, 5:30 min, continuous agitation in PhotoTherm rotary processr) but it still doesn't get me very close for other film/developer combinations I have tried, some of which are off by about two stops.

I generally rate films at about 1/2 box speed. HP5+ is my most-used film and I rate it at EI 200. My normal development is 1:3 D76 @ 68 deg for 14 minutes with 2 inversions each minute. I also use Delta 3200 at EI 1600 (I don't get all of the shadows, but then again I only use it when I really need speed).

The answers to your initial questions are yes, yes. If you are finding the the EI of your film, which yeilds a .1 over FB+F,is less than the films stated ASA then you are doing something right. I have been using Hp5+ for 15 to 20 years. Everytime I chnge developers I do a new film speed development test. Its so easy. Only 1 developer has yeilded a tested soeed of 400ei with Hp5+ and that developer was FG7 with the 15% sodium sulfite solution. All of this varies on many things such as developer, shutter accuracy, thermometer accurracy, meter accurracy. So it happens that almost everybody who does a film speed and develpment test comes out with different results, because of the almost infinite variables. By the way, develop in distilled water. Otherwise, development times will vary with hardness of water and other stuff in the tap water. My synopsis of 400 speed films is that they range in speed from 200ei to 320 ei.

Hi again Alan,

 

We don't care what the film manufacturer says! This is evaluated by a lensless system under perfect conditions with no lens flare, no camera interior flare, and various other imperfections of the system.

 

As photographers, we have to take into consideration our working conditions which I assure you are different from Kodak and Fuji.

 

WE base our work on the reproduction of the neutral grey card at the GBar (contrast) appropriate to our enlarger and print material. This often requires a slight loss of film speed and a development that works for us in our situation, not necessarily that of the manufacturer.

 

Lynn (again)

This is getting too complicated.

 

"If I meter a uniform surface does the meter "assume" that this is zone V? :

 

Yes.

 

"A related question: Dos zone V correspond to an assumed 18% reflection"

 

Yes.

 

You also asked about whether the developer matters or not. Yes, it does. A given film responds differently to different developers.

 

You also asked about different folks getting different results. This is quite common, and it is also quite common for the results to be lower than the manufacturer's suggested speeds. I shoot FP4 roll film at 125 (same as manufacturer's speed) and FP4 sheet film at 100 (or even 80). I shoot HP5 (400 ASA)at 250, and Tri-X (320 ASA) at 250.