Exposure using BTZS

[AndreasT]

Hallo all,
I am sure this has been answered somewhere somehow but I could not find an answer. Now here is my problem.
I have been calibrating my film for a few years now using a similar method as Phil Davis.
Recently I read BTZS Edition 4 and I liked the idea of Phil Davis using an incident light meter to determine SBR and development.
Now the idea of doubling the film speed for the shadow light metering makes sense to me and using this method worked so far for me.
However I have not used it in a +1, or a +2 situation till now.
My thoughts are if you have a dull lighting situation and need a +2 development and use the doubled film speed you will in fact under expose the film by one stop. Since you have five SBR`s/zones being exposed on your negative and if you double the film speed the lowest zone will drop of into the flat part of the curve and will be lost.
Is this right or have I missed something somewhere?
As far as I am concerned the BTZS works where the SBR is 7 or more. However if the SBR is only 6 the film speed should only be multiplied by 1 1/2, and with 5 SBR the film should be exposed by the film speed determined during the film testing.
I would be grateful if someone could push me in the right direction.
Thanks.

 

[Sirius Glass]

Make life simple: Shoot box speed and meter the area that you want to be medium gray. Not only does this work, but also there is not need to do all that mindless testing. It only requires that one realize that the film manufacturer has done than one can ever do and knows more about its products than one can ever learn.

I found that the BTZS books make excellent tinder for lighting fireplaces.

Steve

 

[AndreasT]

Testing is not mindless, it saves time in the darkroom.
Anyway that is not the kind of answer I am looking for!

 

[markbarendt]

I'll vote for simplicity too.

Try this, use whatever EI you normally like for a given film and Incident meter normally, i.e. get the meter in the main light that your subject is in.

Set your lens to match the meter reading, no math, no gymnastics.

Then take 2 shots, do not adjust the camera in any way for the second shot, just shoot, flip the holder, and shoot. Note your best guess for development on the holder.

Develop 1 sheet per your notes, if it's right you are done, if it needs more or less or has a defect use the second sheet appropriately.

 

[juan]

I bought the BTZS software, which, after the initial testing, accounts for those variables. I've shot many times at SBR 6. I could not make sense of BTZS without the software.
juan

 

[Christopher Walrath]

If you're concerned with +2, why not place your subject zones 3-8 and +1.

 

[AndreasT]

Thanks all for your ideas. Its just that what I have been wondering did Phil Davis make a mistake or am I.

 

[Christopher Walrath]

I'll have to brush up, but I figure using the Zone System or whatever other system a photographer might employ, the subject can be made to fit the film over 90% of the time.

 

[frednewman]

Hi AndreasT - Wow that takes me back to when I first learned BTZS in the early 90's. I have been using an incident meter since then and recently sold my spot meter as it was collecting dust from never being used. Most photographers using BTZS, do a BTZS film test and then use the Expo/Dev software for their exposure and development information. Phil Davis realized that the procedure you are describing was a lot of work and he first programed a Cassio FX-795 scientific calculator to be an exposure computer. The actual program was written up in Photo Techniques many years ago. When the Cassio calculator was discontinued we were fortunate to have some program the palm pilot for the expo/dev program. The new program was an improvement over the old program, as it imported your film speed curve, developing time curve and reciprocity information. Phil Davis had calculated reciprocities for about 80 film and developer combinations. This was written up in the D-Max Newsletter, Volume 9, Issue 4.

Phil Davis liked the idea of having an exposure calculator using the data from your individual film test, as it enabled the photographer to concentrate on the image in the groundglass and not have to do all the exposure calculations by hand. The real advantage of this is that when you are out photographing is that for metering all you have to determine is white and black with detail (using either an incident or spot meter) and the expo/dev program calculates you exposure, including reciprocity and your developing time for that exposure.

I have started a series of videos on youtube.com on the expo/dev program and the film testing service offered by the View Camera Store and the plotter for PC program that has been described by Phil Davis in his BTZS book 4th edition and in his BTZS Video Workshop. To find the videos on youtube.com, just do a search on the word "viewcamerastore".

What I really like about the BTZS system is that when I teach a BTZS Workshop or work with photographers doing film testing, they can get really good negatives right in the beginning without any trial and error. It really makes teaching BTZS very enjoyable when you see a photographer that has never used a view camera and when they process their first set of negatives and they get really good negatives right in the beginning I saw why Phil Davis loved teaching so much.

I hope this helped. Please email me or ask more questions here about BTZS.

Fred Newman

 

[StigHagen]

Will BTZS software be available on iphone or android platform?

 

[frednewman]

Hi StigHagen

Possibly somewhere in the future. One of the major problems is getting your film test into the expo/dev software on a device like the iphone. I do have someone looking into it, but if it happens it will be a while. In the meanwhile there are plenty of used palm pilots on ebay for a very reasonable price.

Fred Newman

 

[AndreasT]

Thanks for your reply frednewman.
I have tested my films using basically the same methos as explained in BTZS even before I had ever heard of it. I used to use a incident meter and often got wrong results because I usually used the light reading as my exposure value. I always wondered what the stuff is going on here. Since I have read BTZS I now know why. Since I have been using the Phil Davis method my negatives till now are spot on. Even better than when I have used a spot meter like in the more classical zone system. As far as I am concered one should understand both to use them as desired and required. However my little mind still can not do the maths how the doubling the film speed when doing a shadow measurement when a +1, or +2 development is needed. I still thing that is where it fails resulting in a underexpose but only in these situations.
As life plays with one I have not recently had the opportunity in the field to try this out with taking two exposures at different speeds. I will stay on the ball, and see what happens.
Maybe it just hast to mack click in my head.
Thanks all.

 

[c6h6o3]

I never vary exposure to control contrast. In fact, I never vary exposure at all. I use the same film speed every time and always place the shadows on Zone IV. I meter the shadows, place them on Zone IV and take the picture. Easy. Since the light may have changed while I was setting the lens, loading the holder and pulling the slide, I wait until after the exposure is made to meter the highlights. I'm always metering highlights closer in time to the instant the exposure was made than I would be if I had done it beforehand. I then use the highlight reading to determine how I'm going to develop the negative. Even if the highlight reading is dramatically different from what it would have been when I metered the shadows, the shadows will be the same.

I expose for the shadows. I don't need any information about the highlights to take the picture. I develop for the highlights. I don't need any information about the shadows, film speed or exposure to develop the film.

I glanced at a Phil Davis book once. WWWAAAYYY too much work. It's really so much easier than that.

 

[frednewman]

Hi AndreasT

Take a look at the video on using the expo/dev software on youtube.com. It does all the math for you in the field and it calculates your exposure, including reciprocity and how long to process that sheet of film. Phil Davis liked the idea of automated exposure and development information.

Fred Newman

 

[vertex ninja]

...However my little mind still can not do the maths how the doubling the film speed when doing a shadow measurement when a +1, or +2 development is needed. I still thing that is where it fails resulting in a underexpose but only in these situations...

Don't post here much because I scan, but visit often for the knowledge. Anyway, I've been going over the book recently and my understanding is that because you meter the shadows it doesn't matter if there are 5,6,7,12 zones. The longer development pushes the highlights and midtones up and barely touches the shadows. As development time increases you lose the highs not the lows. So by +2 development you are placing your 5th stop at the rough density of what your 7 would normally be. At least that's what I got from it.

 

[AndreasT]

Yes that is true but when we observe the +2 curve which has a gradient of about 0.8 there are basically 5 zones and if we use the BTZS method we actually half the expose because we are measuring the shadows. Now if we do that the bottom zone would move left off the steep part of the curve and thus be underexposed. The +2 development would raise the rest but not the darkest zone.
That is how I figure it. Anyway I am still using the BTZS method and will evaluate my negatives and see the outcome. Besides I may go on and purchase the BTZS stuff because I do like the idea and with more or less normal contrast ranges I have gotten good results.

 

[vertex ninja]

Yes that is true but when we observe the +2 curve which has a gradient of about 0.8 there are basically 5 zones and if we use the BTZS method we actually half the expose because we are measuring the shadows. Now if we do that the bottom zone would move left off the steep part of the curve and thus be underexposed. The +2 development would raise the rest but not the darkest zone.
That is how I figure it. Anyway I am still using the BTZS method and will evaluate my negatives and see the outcome. Besides I may go on and purchase the BTZS stuff because I do like the idea and with more or less normal contrast ranges I have gotten good results.

We're talking about incident metering right? If you incident meter the shadows you will always overexpose without some compensation, regardless of how you develop or how much SBR the scene has.

 

[marco.taje]

If you incident meter the shadows you will always overexpose without some compensation, regardless of how you develop or how much SBR the scene has.

Not really, in my limited experience. After reading Davis' book -and the time it takes to "digest"- I've settled on an incident pseudo-btzs system. I admit I'm too lazy to do the sensitometric testing (hence the "pseudo"). Yet, exposing as Davis suggest in his incident system DOES work flawlessly, and to me this way is much more error safe than a traditional spot meter approach (which I did for a while, as well).
In the N case, when the incident meterings of shadow and light differ by 2 stops, I found that the film behaves much more in the manufacturer stated way. Let me try to make this clearer, I believe it's very important: we usually read that a film's box speed should be generally cut in half to obtain a negative more consistent with a zone system approach. Well, think of what we're doing, when we incident-meter the shadows and "close" one stop (or double EI, as Davis puts it): we're actually (in N conditions, I say again) incident-metering the lights, which would be a "normal", non btzs metering, and HALVING EI. Eureka!
Now, maybe it's coincidence, but by using this method I found I can set my meter at each film's box speed and get the shadow densities to print just right.

For AndreasT: I surely have much less sensitometric experience than you have, but as I understood Davis' publication, you still have to correct a bit your EI (even when doubled for incident metering) when changing your development.
Personally I don't like the idea of doubling the EI. I usually set the meter to the proper EI, meter the shadows and expose for one stop less. In the N case, it's a pleasant situation because you meter for lights and shadows and then actually expose for their average.. But either way you do it, it is because this way the toe region is CORRECTLY placed; it would not make any sense otherwise. So I'm not understanding your "if we do that the bottom zone would move left off the steep part of the curve and thus be underexposed. The +2 development would raise the rest but not the darkest zone." part.
That is not the case, as I understood. You're halving the exposure because we're assuming that a film, normally developed, shows a range of usable densities equal to about 7 stops. If incident meters, as it seems, assume a 5-stop range, this double reading and exposing inbetween is just making these two ranges match. This is why I don't like thinking of "doubled EI". If I leave the EI as it is, I do get the feeling that I'm exposing somewhere inbetween the shadow and lights meterings. It helps me visualize better, one thing that Davis' method does not, in my humble opinion.

I hope this makes a bit of sense to you, it's not easy to explain..

 

[vertex ninja]

Not really, in my limited experience...

Here is my thinking, If you find through testing that your EFS is 400 and you set the meter to that and then set your exposure to the shadow setting without any compensation or adjustment you will overexpose. You are effectively placing the average of your shadows to your middle zone, not the average of the whole scene.

If you measure a SBR of 7, say EV 2 for the shadows and EV 4 for the light, you set you meter to the EV2 setting and back off one stop. Your zone 4 is now at EV 2. You then have 3 stops under that reading in your shadows. Assuming you do this for all scenes, you will always place the incident reading of your shadows at zone 4. In a high contrast scene you have to pull development and your shadow zones also get dropped down, that's why there is a lower EFS for high SBR and a higher EFS for low SBR; they counteract the changes the development causes to your film speed. Is my understanding correct? :confused:
Edit: just looked over my 4th edition and this is basically what is said on pages 131-133

I think I know what AndreasT is saying. In a SBR5 scene the shadow reading and the light reading should in theory be the same, but just playing around trying to find some light where the meter behaved like that is proving very difficult.

Anyway, I'm just thinking out loud. I picked the book up a year or two ago, read through it and decided it would be hard to effectively implement with roll films. I vowed to shoot my 4x5 more this year, so I grabbed my Gossen Luna Pro F and started going through the book again. I'm far from a BTZS expert, and would really like a definitive answer to AndreasT's question too.

 

[frednewman]

For some reason it seems that everyone is hung up on the doubling of the film speed in using the incident system. That was done in the original teaching of the BTZS system over 20 years ago. Unfortunately Phil Davis's had health problems and was not able to work on a 5th edition of the BTZS book. He wrote about using the expo/dev program in Photo Techniques magazine.

When I started working with Phil Davis, he didn't even discuss that. It was discussed when he originally taught BTZS, before the plotter program. Back then everything was plotted by hand and the workshop took about 2 weeks.

Once Phil did the exposure program for the Radio Shack PC-6 (later the Casio FX-795) and the original plotter program - it changed everything for BTZS. Now all the density reading from the film and paper tests were entered into the MAC (original plotter program). All the exposure readings were entered into the PC-6/Casio FX-795.

For figuring out your SBR you first set your meter to asa 100 and set your meter to the EV (exposure value). With an incident meter you meter for whites with detail and black with detail. You have to read the chapter on gradation in the BTZS book 4ht edition to understand why Phil wanted you to meter for the whites and blacks with detail. When using a spot meter you want to do your readings for zone 7 and 3.

So to figure out your SBR using an incident meter, you subtract the low EV from the hi EV. For example if the the hi EV is 14 and the low EV is 12, you get 2 (14 - 12 = 2) and you add 5, so 2 + 5 = 7. An SBR of 7 is your normal subject. For a contrasty scene lets say the hi EV us 14 and the low EV is 10 you get and SBR of 9 (14 - 10 = 4 and 4 + 5 = 9. That would a and SBR of 9 and the would have 2 stops more contrast than a normal scene.

For a scene in the shade and you get a hi reading and low reading that are the same - for example when both readings are the same EV 10, so 10 - 10 = 0 and 0 + 5 = 5. That would be a typical reading in the shade.

All the BTZS students were fortunate in that we now have the Plotter program for PC and the expo/dev program for the Palm Pilot. Once these two programs were available to to the BTZS students, manually doing the exposure using the incident meter was history. At the BTZS workshops, once the film testing was complete the results were put into the expo/dev program and the rest of the workshop was spent metering and photographing.

I have a few videos up on youtube.com on using the expo/dev software and the plotter program for pc. These videos can be found by doing a search on the word "viewcamerastore".

The BTZS film test is just processing 5 rolls/sheets of film, so the film test is the amount of time it takes you to process 5 rolls/sheets of film. When using the BTZS 4x5 film tubes your film test takes about an hour for the processing. I don't see that as being a lot of work to get negatives that are friendly to print.

I have plans for videos showing incident metering in the future.

Fred Newman