BTZS metering/exposure problem

[michael_mutmansky1]

Hello group,

 

Maybe I�m not understanding something here�

 

Using the BTZS program for the Palm devices, I have been having

difficulty getting consistent results in my negatives, and I think I

may have discovered the source of the problem. What I need to know

is whether this error is a result of a programming error, or a

misapplication (on my part) of the Zone System.

 

Suppose you set the program for �generic 400 speed film�, flare

factor = .02, correction = 0, and paper ES = 1.0.

 

Then suppose you meter a scene, find a shadow at EV 5, and set that

as Z3, and your highlight is EV 7, set to Z7. This gives you an SBR

of 3.5. Then you meter a middle point in the scene and it says EV

6, which will fall at Z5 (right in the middle). That�s a pretty

flat scene, and will require some strong expansion.

 

Fine. Continue on to Working Data, and set an aperture of f11, and

the computer suggests an exposure of f11.3 at 1/4 second. (Let�s

keep the exposures out of reciprocity failure range for this

example.) If you�re following along on your own device, you should

get the same results if you have all the input data the same.

 

Now suppose that take that photo, and then recompose slightly so

that when you were metering the scene, the old 'shadow' point is no

longer there, and you really had a partial-range photograph (high

key) that you wanted to make. Using the same numbers as before, you

metered the middle reading and assigned it to your new �lo� point,

but instead set it to render as Z5. So, shadow EV 6 set to Z5, and

highlight EV 7 set to Z7. This results in the exact same SBR, and

intuitively, if you want it to render that same as the previous

image, it will require the EXACT SAME exposure and development.

 

However, continue on to Working Data, and suddenly, the suggested

exposure has jumped to f11.3 at 1/2 second, resulting in the

overexposure of the negative.

 

As I said, since I just assigned the meter readings to the very same

points on both negatives, I don�t see why I am getting a seriously

different exposure recommendation. Is this a programming flaw in

the software, or am I not completely understanding the ZS as Phil

Davis teaches it?

 

Help would be appreciated�

 

 

---Michael

[brooks short]

Michael,

 

I'm not familiar with the BTZS software you are using in your Palm Pilot. Do you have a URL for it? I'm interested to see what it does for Zone work besides just adding confusing information.

 

But if you have determined your shadow placement and highlight placement for one shot and then reframe your shot excluding the shadow area from the first shot, but still want the same placement of tones.....whew !...why not just shoot at the same exposure as the first shot? Assuming the light hasn't changed and you haven't changed your mind about tonal placement, just shoot it the same.

 

Or if the info from your software concerns you, just shoot a bracket.

 

Now if you want to redo your shadow choice and placement then a new exposure and development would be indicated.

 

Personally, I'd just do a normal Zone placement of the shadow area and development indication for the highlights and not even invite the Palm software to the party.

[jorge_gasteazoro5]

And I thought the BTZS was supposed to be easier to use after you did all that testing...lol..

[michael_mutmansky1]

Brooks,

 

You're missing my point. This example was a test to confirm why I am getting overexposed negatives when I have a narrow range of zones to work with.

 

In most cases, I am not in a situation where I am trying to make two identical images, but I only have the conditions of the second example, that is, I have a high key scene that does not have a legitamite Zone 3 shadow, it really has a shadow that should be placed at Zone 5.

 

My examples show that (from my intrepretation) even though I should be calculating the exact same exposure and development for both examples (one a full range scene, and one a high key partial range scene with the exact same lighting conditions), the results of the calculations are not the same.

 

I do like the program and interface, and I like that it logs my negative information for development. I can enter my zone readings and working aperture in about 10-15 seconds, and get an exposure solution rapidly. I spend much more time deciding on my metering points and my zone placement than I do working with the computer.

 

However, if I'm not getting accurate exposures, then I'll probably go back to doing the ZS by hand.

 

---Michael

[brooks short]

Michael,

 

Sorry if I misunderstood your inital example. I think you did say that you were simply re-composing a view of the same scene.

 

Any way, here's a wild guess as to what your software might be trying to say. I have no idea if this is indeed the case but since the program is telling you that you need 1 stop more exposure for the second scene it might be a possibility.

 

Maybe the software is written in a way that does not consider Z5 as a shadow. Maybe the software will only allow you to consider Z4 and below as shadow areas. When you try to place a shadow on Z5, the software may be saying Z4 is the brightest zone that it considers to be a shadow

 

If that's the case then indeed the software has a glitch.

 

So where can I check this software out?

[j._o.]

"The program requires EV�s with the meter to be set to ASA 100. The

recommended exposure is adjusted for the value input in the Constants screen. The instructions nowhere note that the film speed to be used depends on the subject luminance range. Davis makes much of the fact that the proper film speed depends on the subject luminance range, with careful testing and graphing techniques laid out in excruciating detail; however, the program seems to make no use of these speeds. Of course one can input a custom film and specify its speed on the Constants screen, but I think that few users will be aware that this

is something that they must do, and must do for each subject luminance range. The effect of this omission is that users will make non-optimum exposures and for short subject luminance ranges, will find that the densities produced are larger than they anticipate."

 

-- Bob Wheeler, from his review of the BTZS software

 

Even if the above quote does not contain the answer to your mystery, Wheeler finds that in other situations the program routinely underexposes (but not by much, from what I understood). He also takes issue with some of the DOF calculations it makes.

 

I haven't read BTZS, so I'm not qualified to say whether this is a calculation that Davis intends.

[michael_wellman]

Michael,

 

I have used the BTZS Casio Computer for four years. Last year I upgraded my PDA with the program. I have found that the results to be alomost identical. It's a wonderful system and has provided me with consistent negatives.

 

I have read Phil Davis book, but I've never really digested it all. It's kind of like reading a company report. A lot of good information there if you can wade through it all. I changed over to pyro developer a couple of years. Since you can't do the film testing with pyro staining I've put BTZS to the side, but I have stayed with their calculator.

 

Unfortunatly I left my PDA at work, but I ran your numbers on the Casio and got different numbers than what you show. For your first example I came up with 1/4 sec @ 12.6. If you use a ES of 2 you will get 1/4 @ 13.6. For your second example I got 1/2sec @ 12.6. A full stop more (which I found very interesting and would like to know why as well).

 

You should also know that the program has the film characterstics of TMX, TMY, and TRX built into it. So, if your using a non Kodak film you shouldn't plug in an ASA of 100, 320, or 400. Subtract or add 1 (ie. 401 or 319).

 

It is also very important that you do your own testing so you know which numbers are best to plug in there instead of plugging random numbers in. For example, a ES of 1 seems to low for me. Also, a flare factor of 0.02 is for a normal situation, but if your in such a low contrast area your flare factor may be much lower and this will affect your outcome.

 

The best person to talk to is Fred Newman at "The View Camera Store". He should be able to anwser all of these questions much better than I or anyone else has to date. Of course if you didn't purchase the program that may be a problem. Best of luck.

 

Michael

[michael_mutmansky1]

Michael,

 

I should have been more specific on the f-stop readings. the program in giving me a reading of f 11 1/3 which is about the same as your f 12.6.

 

I have actually sent an email to Fred Newman, and I think he will forward it to Phil Davis, but they are both at a workshop, so I won't hear back from them for a while. I also wanted a 'unbiased' opinion of whether I have an inaccurate understanding of the ZS.

 

Information on the program, (called expodev) is available on Darkroom Innovations' website.

 

As a side note, the issue about film speed shifting with the development adjustment is of concern to me, because my tests of the developer I am using with the HP5+ indicate that the film speed only shifts about 1/3 stop from a SBR of 12 to an SBR of 4. So, I'd rather it not try to accommodate a 'typical' shift, since my film/developer has almost none.

 

I am using a staining developer, so my ES value of 1.0 is actually large enough to get me into Pt/Pd range, which is what I print.

 

It also prints very well on MG paper with a #3 filter, so I can accommodate both if I wish to, although right now I only proof in silver.

 

 

---Michael

[michael_mutmansky1]

Michael,

 

I should have been more specific on the f-stop readings. the program in giving me a reading of f 11 1/3 which is about the same as your f 12.6.

 

I have actually sent an email to Fred Newman, and I think he will forward it to Phil Davis, but they are both at a workshop, so I won't hear back from them for a while. I also wanted a 'unbiased' opinion of whether I have an inaccurate understanding of the ZS.

 

Information on the program, (called expodev) is available on Darkroom Innovations' website.

 

As a side note, the issue about film speed shifting with the development adjustment is of concern to me, because my tests of the developer I am using with the HP5+ indicate that the film speed only shifts about 1/3 stop from a SBR of 12 to an SBR of 4. So, I'd rather it not try to accommodate a 'typical' shift, since my film/developer has almost none.

 

I am using a staining developer, so my ES value of 1.0 is actually large enough to get me into Pt/Pd range, which is what I print.

 

It also prints very well on MG paper with a #3 filter, so I can accommodate both if I wish to, although right now I only proof in silver.

 

 

---Michael

[michael_mutmansky1]

Michael,

 

I should have been more specific on the f-stop readings. the program in giving me a reading of f 11 1/3 which is about the same as your f 12.6.

 

I have actually sent an email to Fred Newman, and I think he will forward it to Phil Davis, but they are both at a workshop, so I won't hear back from them for a while. I also wanted a 'unbiased' opinion of whether I have an inaccurate understanding of the ZS.

 

Information on the program, (called expodev) is available on Darkroom Innovations' website.

 

As a side note, the issue about film speed shifting with the development adjustment is of concern to me, because my tests of the developer I am using with the HP5+ indicate that the film speed only shifts about 1/3 stop from a SBR of 12 to an SBR of 4. So, I'd rather it not try to accommodate a 'typical' shift, since my film/developer has almost none.

 

I am using a staining developer, so my ES value of 1.0 is actually large enough to get me into Pt/Pd range, which is what I print.

 

It also prints very well on MG paper with a #3 filter, so I can accommodate both if I wish to, although right now I only proof in silver.

 

 

---Michael

[jorge_gasteazoro5]

"I am using a staining developer, so my ES value of 1.0 is actually large enough to get me into Pt/Pd range, which is what I print.

It also prints very well on MG paper with a #3 filter, so I can accommodate both if I wish to, although right now I only proof in silver. "

 

This does not make sense to me, if you have a negative that has high enough contrast to print in pt/pd then I would think if you wish to print it on silver you would use a #1 or #0 filter. Typically a pt/pd negative has a density range of 1.8 or thereabouts, a grade 3 paper usually can accomodate a density range of 1 to 1.2, how come the higher grade?

[michael_mutmansky1]

Jorge,

 

I recommend you do some research on staining developers. It's commonly known that the stain acts as a selective filter, more strongly blocking UV light than visible light. My research with this film and developer has shown that it is effectively 50% more dense under UV than visible.

 

I have never aimed for a DR of 1.8 with my pt/pd negatives, that's too high to be comfortable using platinum in my opinion. I aim for 1.4 . Additionally, it is much easier to coax a DR of 1.4 out of a negative than it is 1.8, and that will allow a much more broad range of shooting conditions with the film.

 

---Michael

[brian_ellis3]

I used Phil's program in the Casio computer, the predecessor of the Palm, for about three years. Eventually it broke, Radio Shack couldn't fix it, so I went back to more traditional zone system work. Frankly I enjoy photography a lot more without it. It was always aggravating to stand out in the middle of nowhere punching numbers into a computer key board and then letting the computer go through all its cycles, all the while hoping that the light didn't change, or the wind didn't kick up, or whatever.

 

However, turning to your question, the reason for the difference is that you've told the computer two different things in your two situations. In the first situation you say that you meter the shadows at EV5 and place them on Zone III. You meter the highlights at EV7 and tell the computer you want them on Zone VII. However, if EV5 is placed on Zone III, then EV7 is going to be on Zone V with normal development. But you want it on Zone VII, so you're telling the computer to give you an exposure sufficient to put EV5 on Zone III (and a development time thourgh the exposure scale given to you by the computer that will move Zone V to Zone VII). In other words, you have a scene with a three stop range in which you want an exposure sufficient to place EV5 on Zone III and you're telling the computer that you want a negative with a five stop range. The computer will give you an exposure and and exposure scale (from which you derive your development times if the Palm works like the Casio) to accomplish the two stop expansion that you're telling the computer you want.

 

Then in your second situation you tell the computer that you now want an exposure sufficient to place EV5 on Zone V (i.e. two stops higher than in the first situation) and that you still want EV7 to be placed on Zone VII. You've now told the computer that you have a scene with a three stop range and you want a negative with a three stop range, with the lowest value on Zone V, which is much different than what you told it in the first situation. Since you provided it with different numbers in the two situations, it's going to give you different results.

 

There are two things I don't exactly understand in your question, though I don't know that they're important for purposes of your question. In your first situaiton you say that EV5 is placed on Zone III and EV7 is placed on Zone VII. Then you say you meter a mid tone at EV6, which will fall on Zone V. That's incorrect. If EV5 is placed on Zone III then EV6 will fall on Zone IV, not Zone V. However, the midranges of the scene are unimportant in determining your exposure. Once you place the low value on a particular zone (EV5 on Zone III in your first example) the midtones will fall on whatever zone they fall one without any help from you. In other words, where you place the lowest value will determine the zone on which all other values for purposes of the exposure. Secondly, in your first situation you say the SBR is 3.5. In normal terminology the SBR in the first situation is 3. You're probably reading 3.5 from the computer. Phil uses the term "SBR" in a way that is different from its normal meaning. I found that very confusing and I paid no attention at all to the SBR number show on the computer screen. You don't need it for anything. All you need to know is the exposure and the development time, both of which the computer gives you without worrying about what the computer says the SBR is.

[howard b. schwartz]

michael,

 

if i understand your question, it can be simplified and i think, explained. in your first example, if you place ev5 on zone III, and ev7 on zone VII, you are visualizing a scene with a five zone range (III, IV, V, VI, VII). your ev readings are three apart (5,6,7). according to classical zone technique, this is a n+2 negative. you are expanding the exposure to five zones. since you are going to use more than normal developement, less exposure will be needed than for N developement. your palm reads f11.3 @1/4.

 

now you place ev5 on zone V and ev7 on zone VII. there is a three zone range (V, VI, VII)and your ev readings are three apart (5,6,7). the number of zones is equal to the exposure values. this is N developement. your palm reads f11.3 @ 1/2. the extra exposure is needed because you are doing less developement than in the first example.

 

in the first example you are giving more developement and therefore less exposure is needed than in the second example. the 1/2 second difference in the two expamples may make sense.

 

as far as "overexposure of the negative" that you discuss, what is the density range of both negatives? this will help in determining whether your negatives are okay. please let me know if this helps. howard

[howard b. schwartz]

sorry, in my response the difference in exposure should be 1/4 second difference in exposure.

[brian_ellis3]

You can't place EV5 on Zone III and EV7 on Zone VII through the exposure. You can only place one EV on one zone when making the exposure. Once you place one EV on one zone, all other zones fall wherever they fall based on the one EV you chose to use and the zone on which you chose to place it in making the exposure. For example, if you decide to place EV5 on Zone III, then EV6 is going to fall on Zone IV, EV7 is going to fall on Zone V, EV 8 is going to fall on Zone VI, etc. There is nothing you can do to change those zones through exposure. The only way to change those zones that were determined by the exposure is through development. When Michael said that he placed EV5 on Zone III and EV7 on Zone VII in making his exposure(an impossibility) what he meant was that he told the computer to provide an exposure that would place EV5 on Zone III and a development time that would move EV7 from the Zone V on which it fell through the exposure to the Zone VII on which he wanted it to fall. That expansion of the scene's actual values would be accomplished through development. In general, the computer bases the exposure on the low value (which is why he got different exposures depending on whether he placed EV5 on Zone III as in the first example or on Zone V as in the second example) and the exposure scale (from which someone who uses the computer determines his or her development time) on the difference between the low EV/low zone and the high EV/high zone, though there is some connection between the exposure and the development time since the exposure has to be adjusted to some extent to take the increased or decreased development time into account.

 

As I mentioned in my earlier message, Michael made an error when he said that in his first example EV6 would fall on Zone V if EV5 is placed on Zone III. In reality if EV5 is placed on Zone III then EV6 will fall on Zone IV, not Zone V. So this kind of messed up his second example, where he says that he placed EV6 on Zone V and that he was providing the computer with the same numbers as in the first example, which he really wasn't.