question on 100mm macro and .31m switch

[jonnyhorizon]

i just got a new 100mm EF 2.8 macro
i think i am in love
there is a switch where you can select .31 to infinity or .48 to infinity
why wouldn't you always leave it on the .31 setting? ...

[SeanDempsey]

For when you don't want it going through a full focus cycle when seeking for an AF.

Like with the 100-400, if I know I Am going to be doing birds that will be 50-60 feet away, I set the focus to 6 meters to infinity, instead of 1.8. That way, if the AF has to seek, it only seeks in that range, and doesn't waste time in the lower range.

My Sigma macro does the same thing. You can set it to focus all the way, or 1.3 feet and up, or 1.3 feet and down. Helps reduce AF seeks.

[jonnyhorizon]

god this is a great forum
thanks...