That was true of the Weston Master meters. It may still be true of the separate meters from Sekonic and others. However, most camera meters that I know of are calibrated to expose a less reflective surface to middle gray.
I must ask this question. where is everyone getting the idea that incamera histograms are not acurate ? because i just shot some test
shots with my 12 yold olympus xz1 raw file incamera RGB histogram then took the file into FRV and it again matched the clipping EXACTLY
so im very suspect that its not true that incamera histograms are not acurate. or maybe its because i buy good quality cameras .
In my case, from testing. Here are a few of the cameras I've tested: Sony a7, a7II, a7III, a7R, a7RII, a7RIII, a7RIV, a7S, a7SII, a9, a9II. Nikon D3, D4, D5, D800, D810, D850, Z6, Z7, Z9. Fuji GFX 50S, GFX 50R, GFX 100, GFX 100S.
About 12.5%, which is three stops down from full scale. But the key thing is that it can vary with camera model number (and, I suppose, with camera serial number, but that is going to be a smaller effect).
It was partly also related to your earlier comment:
"there is very little or no penalty when "underexposing" by keeping the ISO a few stops lower than the maximum possible while keeping the exposure unchanged."
which made no sense to me because I cannot see how you can underexpose while keeping the exposure unchanged.
I make no apologies at all for including the definition of "exposure" I use in my posts in the interests of transparency and clarity.
Too many beginners, and even some who should know better, confuse image lightness and exposure and incorrectly use them interchangeably as if they meant the same thing when they do not. Very often when I question them to clarify what they mean by "exposure" so that their posts will actually make sense, they either run away or come up with all sorts of wishy-washy descriptions because they do not really know what exposure actually is.
At least with my posts people will know exactly what I mean by "exposure" and "optimal exposure" so there is no misunderstanding. Now, whether they agree with me or not is a totally different matter 🙂
Funny that you should say that. because the exposure settings on that camera were always different than any other camera i owned. now i will compare it to my a74.
So in the future if I posted something like "....contemporary camera meters are calibrated to output ~12.5% grey image lightness....", would you be comfortable with that?