In macOS Finder it says a photo taken at f/2.8 has an aperture value of 3. What is an aperture value, and how is it different from f-stop?
The Exif standard says that:
which is also:
There is even a nice conversion table:
However, looking at my own photos (EOS 70D), I find that the exposure value and the FNumber are close to each other but not always equal, so this doesn't follow the table below for apertures => f/8. So I wonder if for Canon, these tags wouldn't be:
- F Number: what you (or the auto-exposure) have set the camera to
- Aperture value: actual aperture taking in account actual focal length (that changes with focus....)
The AV (Aperture Value) is an expression that tells how many stops away from f/1 an aperture is.
Since f/1 is zero distance from f/1, it has an AV of zero (0)
Since f/1.4 is one stop slower than f/1, it has an AV of one (1)
Since f/2 is two stops away from f/1, it has an AV of two (2)
Since f/2.8 is three stops from f/1, its AV is three (3)
... and so on.
For instance, f/16 is eight stops slower than f/1, it has an AV of eight (8).
Apertures faster than f/1 have negative AV. For example, f/0.5 is two stops faster than f/1, and has an AV of -2.