I should point out that what Ilford objectively regards as a speed point tends to be well below realistic shadow separation, because it's still on the toe.
I should point out that what Ilford objectively regards as a speed point tends to be well below realistic shadow separation, because it's still on the toe.
Thanks everyone. I have been using a table I created based on the one provided by Steve Simmons in his view camera book. If I recall properly, he gave one set of times for all Ilford films, which, as noted above, is problematic due to the real differences in the films. I am thinking that I can make a new table using the formula. Another alternative is to use a spreadsheet on my phone to automate the calculations. I know that there are apps out there, but they are based on different approaches to the reciprocity problem. This discussion is helpful.
Michael, Let's say I meter off of a subject that I want to place on Zone VI. That means that I would take my meter reading and adjust one stop to place it on Zone VI, just as always. We would normally expect that 3 1/3 stops below that will fall on Zone 2 2/3. The exposure will register as .1 above Fb+fog if we follow the time determined by using Ilford's factor/formula. Am I understanding properly / making sense?
I should say that most of the situations when I am photographing something under low light conditions and dealing with reciprocity, I look for something I want to register at Zone V and meter that. In that case, the 3 1/3 drop would be zone 1 2/3, which in most scenes would be just fine registering at .1 above Fb+fog. Let it go black!
Last edited by David Karp; 9-Feb-2018 at 17:47. Reason: Added clarification
You didn't ask me, but you should meter for the low value, then apply the reciprocity correction, then divide to get the corrected exposure time. I meter Zone III and then divide the corrected time by 4 to get the right exposure. If you do the reciprocity correction on Zone V, your shadows will be underexposed.
This is a choice, but something else can be done... in LIRF conditions costrast may rise too much, so rather than dividing the corrected time by 4... an N-2 development may be better. Just another choice...Originally Posted by David Schaller
David,
I'm not sure I completely understand the question, but I don't think your second paragraph is correct. Assume you set your meter to the film's ISO speed. Further assume there is no flare. If you meter something in the scene and place it on Zone V, whatever falls on Zone I 2/3 should have a density of 0.1 above Fb+fog in the negative. The Ilford factors should ensure that remains the case when exposures are long. If you instead decide to place the metered object on Zone VI, whatever falls on Zone 0 2/3 should have a density of 0.1 above Fb+fog in the negative. Again, the Ilford factors would ensure that remains the case when exposures are long.
The Ilford factors are designed to maintain a density of 0.1, 3 1/3 stops below the metered exposure.
Don't get too caught up in the underlying theory. The important thing is the Ilford factors ensure that when exposures are long, shadow densities stay the same as they would when exposures are short. Consider the Zone System separately. Figure out your exposure, then apply the Ilford factors.
Ahhhhh. That makes sense. Thank you.
I am going to give these a whirl. Interesting how the factors for FP4+ and Delta 100 are the same, while HP5+ is actually a little better than Delta 400. My wife (an Excel wizard) made a spreadsheet for me that allows me to select the film, input the metered time, and automatically calculate the "corrected time." I transferred the file to my phone, so as long as I have battery power I will be able to use it to make photos.
There it is, to quote the essential Michael R, '...figure out your exposure, then apply the Ilford factors.'
Sorry, I am a simple guy.
Michael,
Let me chime in here (late) with an observation/request for clarification.
As I see it, when I "place" something in Zone III or Zone VI or whatever, it's because I want a particular area of the scene to be rendered differently than "normal," i.e., Zone V. Now regardless of what I'm basing my exposure on, there's a hypothetical Zone V implied. The speed point Ilford is working with is 3 1/3-stops below this; not 3 1/3-stops below whatever I'm placing.
In the example above, "placing" a value in Zone VI would imply overexposing it one stop from Zone V, for whatever reason, but a clear and conscious choice to ensure that area of the scene gets more than Zone V exposure. So... if I'm figuring correctly here, the Ilford speed point is still going to be at Zone I 2/3. The same thing should happen if I base my exposure on Zone II, III or VI (where I'm intentionally underexposing from a Zone V meter reading).
So, do correct me if I'm wrong, because I can't seem to figure this out the way you have.
Change of subject:
One problem with LIRF that gets lost in talk of preserving shadow detail is the contrast expansion that happens with really long exposures due to the proportional nature of reciprocity failure. If one meters and places a value on Zone VI and then gives a really long corrected exposure (say upwards of 4x the metered exposure) and then develops normally, that Zone VI density is going to be way higher on the negative than a "normal" Zone VI density. In essence (if the Ilford factors work as they should), we've produced proper density at the speed point, but now have a really contrasty negative to deal with, one in which our target density (Zone VI) is significantly denser than we wanted. Of course, the obvious solution is to adjust development. However, since the amount of development adjustment likely varies from film-to-film (just as the LIRF factors do), testing this for many films is a lot of work. I'm not even sure that the exposure correction is linear. Add to this Howard Bond's suggestion that no development adjustment is necessary and the subject becomes even more complicated (BTW, I'm fairly sure Bond is wrong here, especially for very long exposures). Kodak used to publish development adjustments in their reciprocity tables.
I've empirically figured out what to do to get negatives that are in the ballpark and can be printed halfway easily with very long exposures for the two films I use most, but have no real quantifiable data. If Ilford wants another project, they could test how to maintain the speed point and a Zone VIII density and publish the exposure and development adjustments for very long exposures.
Best,
Doremus
Perhaps for "street jargon" purposes, the "speed point" could be equated to the transition between Zone 0 and 1 ? I realize this is hardly an ideal explanation. But there is very little pintable value down there.
Drew, speed point is exactly 3 1/3 underexposure from box speed so it should be in the Zone I to the to the Zone II transition.
Before the ISO speed change in 1960 ISO the speed point was in the Z-0 to the Z-I transition, but after 1960 it's only 3 1/3 stops underexposure from what meter says. Books edited before 1960 use the criterion you say, since 1960 things moved one stop.
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