Hi, Julian
"How large is the IR correction required for the EF 15mm f/2.8?"
Lots, I don't have any numbers but the red mark is a long way from
"center", but the focus distance is very minimal. with the 15/2.8
focused
at hyper focus I can achieve focus from something like 3 feet to
infinity at f22.
The focus scale on the barrel that has the DOF scale only goes to f16,
so for
f22 it's a guess. The DOF is so great that the distance window is to
small!!
"Is it larger or smaller than IR correction for the EF 24mm f/2.8?"
It is a larger turn on the barrel but shorter in focal distance. (I
think)
"Is there a formula to calculate the focus shift required?"
Beats me :)???
Ciao,
Dan
> Hi Dan,
>
> You bring up an interesting point.
>
> On my EF 100-400, the amount of IR correct is greatest at shorter
> focal lengths.
> How large is the IR correction required for the EF 15mm f/2.8?
> Is it larger or smaller than IR correction for the EF 24mm f/2.8?
>
> Is it possible that the greater DOF (which is proportional to
> the square of the focal length) can be overcome by a greater
> amount of IR correction required at longer focal lengths?
>
> Is there a formula to calculate the focus shift required?
>
> Cheers
> Julian Loke
>
>
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