If the featureless sky takes up the entire frame, it's the same as shooting a target. It's virtually a flare free situation, or to put it more accurately, free of the effects of flare.Perhaps there is no definite answer. Here's another way to think about the same example. You take a picture of a bright, uniform, featureless mid day sky and expose it to produce an expected net film D of 0.20. In the evening you take a picture of a middle grey, uniform, featureless evening sky and expose it to produce a net film D of 0.20 (so obviously this would be a significantly longer exposure than the picture of the mid day sky). Assume some camera flare in the first exposure leads to an actual net film D of 0.23. Would that occur in the second example too, even though the intensity of light entering the camera is lower? I'm thinking there would be less, or zero flare in the second exposure. Not sure.
You're keeping stray light from entering the camera. The exposure of the white card shouldn't be affected either way. Even with an average luminance range the effects of flare at the point of the white card is inconsequential.Keep in mind this question concerns an in-camera film test with as little flare as possible (aside from some degree of lens flare which cannot be totally eliminated). The aim is to use a brightly lit white card for the entire series of exposures. In actuality, the lens is masked to restrict the projected image to within the borders of the emulsion. In other words, there should be no camera flare. But even though I would be using this mask anyway as an extra precaution, I'm wondering if it is necessary. So my example above would be the equivalent of not masking the lens.
With Adams you come away thinking it's a conspiracy. You should read the stuff I wrote n the K-Factor thread. Here's a page.Regarding the K-Factor discussion in Henry's book, as it happens I re-read that very section today, and I came away just as little understanding as when I first read the book. I wish he had started by explaining what the K-Factor actually is before getting into the ranges, calculations, standards etc. I still don't get what the K-Factor is. The only thing I think I understand is that it is not what Adams said it was. When you read Adams you come away thinking it is just a safety factor built into the meter.
Defining K, part 2.jpg
Henry talks about the various values of K, but he doesn't explain what it is or how it relates to exposure. In Henry's book you come away thinking it's an arbitrary decision by the manufacturer. BTW, he never really defines exposure (or from what I've read so far). I like that he has a bibliography, but he could take the level down a notch and include the titles of the papers. The book isn't for scientific publication.