How to calculate sharpest f-spot on a given lens

[casey warren]

What is the formula for determining what the sharpest f-spot is for any given lens?

for example: I own a Canon 85mm f1.2L and I would like to know how to determine what f-spot to use to get the sharpest picture. From what I've noticed through taking many photos with the 85 is that the sharpest is around 4-5.6 range, but I am curious if there is a mathematical way to determine this number.

[Dave Cooper]

Usually two-three clicks from being wide open.

[Stephen Williams]

What is the formula for determining what the sharpest f-spot is for any given lens?

for example: I own a Canon 85mm f1.2L and I would like to know how to determine what f-spot to use to get the sharpest picture. From what I've noticed through taking many photos with the 85 is that the sharpest is around 4-5.6 range, but I am curious if there is a mathematical way to determine this number.

Hi,

You have to test to get the answer. Identical lenses may differ.

Stephen

[M Olsen]

What is the formula for determining what the sharpest f-spot is for any given lens?

for example: I own a Canon 85mm f1.2L and I would like to know how to determine what f-spot to use to get the sharpest picture. From what I've noticed through taking many photos with the 85 is that the sharpest is around 4-5.6 range, but I am curious if there is a mathematical way to determine this number.

Hi , Stephen has answered your question with the need to test, but as a personal observation I have owned several fast Canon lenses and they all clearly performed at their best at f4.0

[casey warren]

Yeah, I've noticed that 4.0 is pretty darn sharp on the 85mm. I also have a 28-135mm and 5.6 seems to be the sharpest on that, but I will have to do some more testing.

[chuck colburn]

Hi,

You have to test to get the answer. Identical lenses may differ.

Stephen

Yeah, what he said.