Because flare introduces some amount of unwanted density.
But the effect of flare is increasing compression below say Zone V. So doesn't reducing exposure simply move more of the image values into the area where local contrast is compressed?
Who is this Henry you guys are talking about? I couldn't find where he is first mentioned in this long thread.
This is a good example of my earlier topic about the helpfulness of understanding theory. Helpful not so much as part of achieve precision testing. That's not necessary for most photographers. It's helpful in knowing the limitations of the tests.
This can only be true if the photographer shoots with the same lens at the same f/Stop and shutter speed. And this is a good example of my other point about good testing and bad testing. My contention is that speed testing isn't necessary for most and the only testing really needed is for contrast (and that only applies to maybe 10% of photographers). In order to achieve knowable, quantifiable results, the variables and testing conditions must be known and controlled. In other words, scientific testing. Many of the disagreements about testing come from people arguing from different perspectives. It isn't a question of which is more accurate. But there's a big difference between testing for film speed (scientific) and testing for EI. They are different things and have different purposes.Quote:
"any variations introduced by a change of equipment (such as the possible difference in aperture calibration or flare introduced by changing lenses) should be quite apparent if they are significant." - i.e if you have calibrated with one camera, one lens, one meter, one developer, one thermometer, etc introducing a variable such as a different lens will immediately show if flare, for example, is a significant factor. If it is, you then know that you need to re-calibrate for that particular lens by redoing the testing sequence.
Sorry, ran out of time.
As to source, uhhh. ;)
About 80% of flare originates with the subject, but it only exists when there's an optical system involved. There are a couple of different types of flare, veiling has to do with the optical system and camera creating an evenly distributed level of exposure. Another type is ghost which produces an image of the aperture.Quote:
Regarding the sources of flare in testing etc, again, I'm refering mostly to flare caused by the subject/test target, not the lens. The kind of "veiling" lens flare Adams refers to is likely a relatively minor issue with most contemporary lenses.
While flare plays a factor in the determination of film speed, for me it's more about the effect it has on the illuminance range. Kodak's contrast index for normal processing contains a value for flare. Their numbers won't work without it.
When he retired, he decided to equip himself with the appropriate tools and set about testing for the validity of many of the claims made by notable photographers, Zone System writers etc. He published the results in a book called Controls in Black and White Photography.
While the materials he used are mostly outdated, perhaps the most important takeaway is that just because a well respected photographer says something about exposure, development, contrast, chemicals etc doesn't mean we should simply accept it as fact, especially in cases where no evidence, or a proper description of the experiment is given. And the description of the experimental method is very important. Even when presented with data (a characteristic curve for example), if we don't know how the test was done, it is often difficult to conclude anything.
I don't think that under exposing is being suggested, minimizing might be a better description, or maybe giving up the safety factors.
Flare, like flashing, essential raises the lowest values significantly, easily doubling the density, without moving the highest values much at all, maybe 1%ish, you knew that though I'd bet.
Flare, I theorize, like flashing needs to surpass a threshold point to have a significant effect. Less general exposure can help keep flare/flash exposure under the required threshold and therefore affect the image less.