Newbie Question - what does 1.5/3.0 switch do?

[wstaylor]

Upon seeing the EF 70-200mm f/2.8 L lens in person, I was curious what the switch with the settings "1.5 M" and "3.0 M" were for? I'm new to the L series lenses, thanks for any help!

W. Taylor

[Jon]

Minimum focussing distance under AF. If you're going to be working at a distance from your subject, you can prevent if from trying to rack out far enough to focus at 1.5 m, so it'll be able to focus faster.

[wstaylor]

Ah, I see, I think. I'm not sure what you mean by "rack out". So setting it on 1.5 would prevent this?

Thanks

[HJMinard]

Ah, I see, I think. I'm not sure what you mean by "rack out". So setting it on 1.5 would prevent this?

Thanks

He's referring to the internal parts that move during autofocus. When set to 1.5 the lens will move through its entire range (1.5 meters to infinity) while attempting to autofocus. When set to 3.0 it will only move through the 3.0 to infinitiy range. This smaller range results in faster autofocus ... soooo ... if your subject is expected to stay beyond 3 meters, it is better to have the lens set to 3.0.

[RichardtheSane]

Just to add to this the range from 3m to infinity is much less distance for the AF mech to travel than the rance from 1.5m to 3m - about 1/3 IIRC.

So just from a speed point of view with only 30% of the distance you can see why AF is quicker

[gramps]

In other words, unless you are shooting something "close up" (within 1.5 meters) leave it on 3.

[Pekka]

In other words, unless you are shooting something "close up" (within 1.5 meters) leave it on 3.

Of course there is a slight chance of forgetting the switch and having problems getting AF lock on portraits. You wonder what is wrong, then you check the switch: 3m. Done that many times, so on my 70-200 it's always on 1.5 :)