"What does this button do?"

[Riggaberto]

What does the other switch, the one next to the AF/MF do? I dont have the instruction manual for this lens so I dont know.

 

[Patrice]

I'm no Canon expert, but it might be a focus limit switch similar to the Nikon 70-200. Big Mike can confirm that. Have you googled for the info ?

 

[Peanuts]

There may be three buttons. There is the AF/MF, Image Stabilizer On/Off, in addition to one that may say 1/2. I believe 1 is for 'normal' image stabilization meanwhile 2 is for panning.

 

[RacePhoto]

That's the top secret "Focusing Distance Range" switch.

You can set the focusing distance range to 1.4m / 4.6ft to infinity or 2.5m / 8.2ft to infinity. By setting the suitable focusing distance range, the actual autofocusing time can be shorter."

Basically if you are in a situation where you know you won't be focusing closer than 8 feet, you can set it to ignore closer distances and it's supposed to focus faster.

Mode I IS is for fixed objects, low light and when you might not have a stable mount. Things like hand held pictures. Think of it as a vibration correction.

Mode II is for panning and objects that may move erratically.

IS does not stop motion, of the subject. It just attempts to eliminate shake and any movement caused by the camera and the lens. There is a difference.

Nice lens!

 

[Digital Matt]

That looks like the f/4 NON IS, which I have sitting in front of me. It's the focus limiting switch.

 

[fmw]

Shucks, I thought it was the phaser trigger.

 

[Riggaberto]

That looks like the f/4 NON IS, which I have sitting in front of me. It's the focus limiting switch.

Yeah unfortunately it's the non IS . I think the cost is what, like 1/2 or 1/4 the IS version?

Anyway that's the info I was looking for and it's good to know, thank ya.