Thanks, an enjoyable thread. Good explanations of those mysterious “ reduce your EI from 100 to 80 and reduce your development by xyz % “ that turn up in various books. Now I know why these work; at least to a degree, a degree of “works” I mean. Not having a working densitometer I live by notes and adjustment, not maybe the best way but I do keep out of mischief and my prints continue to improve.
Dear ic-racer, I freely admit that I tried (3 times) and failed to understand your original posting ( I speak as a qualified professional photographer and former technical writer for Ilford Limited). However, I must say that the above statements are total nonsense.
Originally Posted by ic-racer
If you determine exposure on the basis of a shadows reading, then (assuming your reading is accurate) you will obtain correct [minimum] shadow exposure. That is all - there is no direct relation between this exposure and the amount of latitude you can exploit, since this depends on the subject brightness range and the contrast to which you develop the film. If the SBR is "normal" (128:1) and the development is "normal" (G bar 0.55) you will record all tones in a printable form but exposure latitude will strictly speaking be zero (it may be one or two stops, even three, if you are willing to tolerate highlight degradation). If you increase shadow exposure, there will be even less "latitude". The only way to increase exposure latitude is to downrate the film's EI and develop to a lower contrast.
In the reverse case, basing exposure on a highlight reading will if done correctly ensure correct highlight exposure (maximum possible while retaining detail). Again, with a normal tone scale, there is virtually no latitude except at the expense of shadow degradation. In the case of a transparency shot for projection, latitude is virtually non-existent, there is essentially only one optimum exposure plus a short range of sub-optimum degraded but perhaps acceptable (under-)exposures. Decreasing the exposure can hardly be considered to be exploiting latitude - there are numerous exposures which will record highlight detail, but shadow detail will be hopelessly dark. There is no meaningful sense in which you can draw on 3 stops exposure latitude in both the under- and overexposure directions!
What exactly is it you are trying to convey to potentially 25,000 other members?
Originally Posted by ic-racer
I would pass this on to folks who are new to film. I lack the skills to put it any other way but, IGNORE IT!! You will experience no gains in your understanding of exposure and development if you don't----only headaches.
The phrase "expose for the shadows and develop for the highlights" is an old, but very true, principle in photography. There's different ways to apply that principle i.e., ZS or BTZS, or simply overexpose and underdevelop, with the latter practice being a much less refined application of the principle than ZS or BTZS. So, get the most out of your film of choice and expose for the shadows and develop for the highlights. It works quite well.
referring to "negative" film, of course.
Originally Posted by CPorter
: you understand why it should work but it doesn't
: it works but you have no idea how
Here theory and practice meet, things don't work and I don't know why
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