I think I understand the basic reason why marked F stops start to become meaningless at macro distances, but I have a related question. Does the skew, that is the amount larger the actual f-stop number is from the marked number, increase or decrease with longer focal lenghts?
That is, if I have a 60mm f2.8 and a 100mmf2.8, both focused to make an object appear 1:1, which will be more skewed from the marked f-stop?
a

AFAIK the Fstop "skew" is mainly linked to magnification not focal length.
Apparent F= F * (1+M) where M is the magnification.

Brian v.

How is magnification described for that formula? is it the usual macro 1:1 as a fraction or
A

amacks wrote:
How is magnification described for that formula? is it the usual macro 1:1 as a fraction or
A

Just as a whole number, so 1:1 would be 1, 2:1 would be 2, etc.