EV = log2(f^2/T) LV = EV + log2(ISO/100)
Question is to those that this is already clear. It is not a math question, it is a photography question about using Light Value.
My puzzlement is "what is the useful use of this LV = formula?"
Clearly it adds effect on EV of ISO relative to ISO 100. But when would we need to use this LV = formula? (specifically, by adding it to EV?) In use, what EV would we add it to?
If we calculate the top EV = part for any existing camera settings (for any exposure assumed useful), fstop and shutter speed used already have the ISO effect in it. Basically, EV is LV, EV at an ISO. But then adding any LV ISO effect would repeat it, incorrectly doubling ISO effect. So "EV" already has the result that I might incorrectly imagine "LV" would add.
If we meter a scene at ISO 800, then we look up that result EV in the standard EV chart, to find the row of Equivalent Exposure settings to be correct in that light at that ISO. Basically, EV is LV, EV at an ISO. Using those settings (which now have ISO in them), we cannot recalculate those settings again (EV we can, but the LV part would repeat ISO, doubling the proper ISO effect.)
What is a realistic example of when we would actually use the LV = formula ? (and not see an incorrect doubled ISO effect?)