I was not following your expression of Fstops and time initially. Lee's explanation clarified that for me.
Regarding your questions, let me begin by answering your question of EV. EV is an expression of Exposure Value and it will be a numerical expression of any combination of Fstop and shutter speed that will give the same exposure to film. For instance F8 at 1/125 second will be exactly the same exposure as F11 at 1/60 second. The only effect will be an increase in depth of field when exposing at F11.
Regarding you question on EI. EI is an expression of Exposure Index or the rating that one gives a given film to afford proper exposure. In Zone System practice, it is common to rate a film at a fixed EI. In BTZS (Beyond the Zone System) practice EI is not a fixed value but it does in fact deviate based upon development of the film.
For instance if we took Efke PL 100 and determined that the EI for N development (SBR 7) was 50 then if we had a N +1 development (SBR 6) the EI would 64 or 75 and for N+2 (SBR 5) the EI of that same film would be 100.
There is another expression that you will encounter---SBR. SBR is an expression of Subject Brightness Ratio. This is the ratio of the shadow to highlight values in a given exposure. SBR in BTZS is roughly the equivalent of N, N+ and N- in Zone system terminology. SBR is a more precise method. It is from the SBR or the contrast range of the exposure that we arrive at the proper degree of development for the film. It is more common to use incident meters then reflective spot meters in SBR practice.
Now taking your earlier example, that scene would have had an EV of 10.5 on your low reading and an EV of 16.5 on your upper reading. It would have been SBR 11 (in BTZS terminology) and N-4 in Zone System. It would have ideally had a compensation of an increase of 2/3 stop in EI and it would have a reduction of development dependent on your testing of your specific film and your specific developer.
The CI (Contrast Index) is a measure of the contrast that the film is developed to for a given printing process or paper. For silver it is .47 to .52.
By way of information, what you did in determining your exposure was to place your low values at Zone II 2/3 rather then the III-IV that you calculated. F22.6 (22 2/3) at 1/2 sec would have been a Zone V placement...two stops less would have been a Zone III placement. That would have been F 22.6 (22 2/3) at 1/8 second. F22 as opposed to 22.6 (22 2/3) at 1/15 second was a Zone II 2/3
Now getting back to your original question on how much to decrease your development for the increased contrast that you encountered in this exposure, as I said earlier it really needs to be determined by you in testing your film and your developer. Had you given a fuller exposure, I would begin, in this example, of appr. a 25 to 30% decrease in time of development...that would get you into the ball park.
However since you underexposed the film, in this case, I would develop the film normally.
Last edited by Donald Miller; 09-26-2005 at 12:47 AM. Click to view previous post history.
Thank you Don sooo very much. It is most appreciated. This kind of information is basic yet I stumble upon it never knowing how to use it. It seems like there is so much to know that I should have studied photography in an orderly manner where in fact I gather bits and pieces of information as I go about my intuitive path and constantly try to fill holes and gaps and those are so huge its hard to see at times beyond them. Thanks!!!
Originally Posted by Donald Miller
Couple of more questions if you don't mind:
You have mentioned "It would have ideally had a compensation of an increase of 1/3 stop in EI" - I am not sure why. Could you explain
About CI, EI and SBR, are the numbers a given data someone have set for all to be used or something everyone can figure out? how? Is the SBR the number of f stops between highlights and shadows?
I am sorry, I made some errors in my earlier post. In the case of contraction (reduced development from normal) the EI should have been decreased by the amount that I indicated. The correct compensation is that as development is decreased (from normal--SBR 7) the EI is decreased and as the development is increased (from normal--SBR 7) then the EI is increased. As I mentioned EI is not a static factor since it does increase and decrease somewhat with altered development...sorry for my earlier errors. I have corrected them.
Originally Posted by Ruvy
In BTZS so long as the testing is done consistantly with the same developing regimen, films and developers the EI and CI are consistant from photographer to photographer. That is one of the benefits of that system. For instance if you were to go to the www.Unblinkingeye.comsite and review the information that Sandy King has provided you should be able to get yourself fairly close in your own practice...so long as you utilize the same practice and materials.
SBR is based on the calculations as outlined in the BTZS volume 4. All of the testing procedures are contained in that volume. The SBR is arrived at by subtracting the low EV from the high EV and adding that result to 5. SBR 7 is considered to be the equivalent of N in Zone System terms. As I mentioned in the earlier post, this applies to incident meter readings. For spot meter readings, further calculations are required. It is a common procedure, once understood, and is consistantly used by those who practice that particular discipline.
Its easy for me to be attracted to logic that creates near perfectly executed beauty. The BTZS seems fascinating at that level and adds another plateau of overwhelming new information and time consuming steps. Just started and still learning to use a 4X5 (making lots of errors) but am most excited for the developing each frame on its own. Likewise got an enlarger and starting to develop and print etc.
Originally Posted by Donald Miller
I am wondering if its wise right now to get in depth to so many subjects when the capacity of my mind is growing in revers ratio to my age ;-) and if not, would it be sufficient right now to assume a less than perfect procedure that will leave time for photographic experience, growth and real work too. If so, what may be the priorities of learning. Until this thread I was pretty much sure of my way. Use simplified zone system by sooting for shadows and developing for highlight by finding out a percentage contraction for each stop over 5. Now I have to think if slowing down and learning more about film should be the right thing. Desiring relatively fast results in not foreign for me so a path have to be found to meet all those new things with my own capacity and personality too.
The late Fred Picker, the founder of Zone VI, once made a recommendation that someone starting out in large format would be well advised to take the first year and photograph only with polaroids. His recommendations were based on the fact that instant feedback was available on both composition and exposure. I understand the reasoning for that recommendation today.
Originally Posted by Ruvy
It takes time to learn enough technically to reach a point of becoming satisfied with the results. That has been the experience of a lot of photographers and it has been true for me.
If I were beginning over today, I would probably seek to do what Picker recommended or I would take Michael and Paula's workshop. They will recommend contact printing because that is what they do. There is no need to limit yourself to contacting print only. The vision portion of their workshop is worth the commitment. Their workshop would probably "jump start" your ability to see. In lieu of that, study lots of photographs by other photographers.
Recognize that all of the technique in the world with a poorly "seen" image is going to result in a weak photograph. Conversely, "weak technique" with the ability to "see" will result in a strong image without the means to express it optimally.
Good luck in whatever you choose to do.
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Originally Posted by pentaxuser
Any light emitting (instead of reflecting ) subject.