70-200mm f2.8L IS - Focus Problem?
 

Hi, Just bought a Canon 70-200mm f2.8L IS and noticed when I zoom full at 200mm to focus and then pull back out to frame I loose focus.

I have to turn a couple of millimeters to refocus, that kind of defeats the purpose of zooming to focus.

I assume this is a back focus type issue? Is this a fault or a characteristic of the lens.
Can anyone confirm this.

Thanks, James

Quick update, I have found that at any zoom range once focused sharp, there seems to be a bit of free play on the zoom ring.

One side of the free play is sharp the other soft, free play travel is about 1.5mm. My other zooms have a bit of freeplay in the zoom ring but it does not change the focus.

Now I found this freeplay I can zoom to 200 focus then pull to 70 twist the freeplay and it is sharp. This must be a defect.

Paid a quick trip back to 'Park Cameras' and they had no more units in, they sold 4 yesterday. 7-10 days for restock.

A young chap had a quick look and agree it was a problem, he only tested it for a couple of seconds and I'm not sure if he was just agreeing with the customer.

He told me to use it until they had restock, so I brought it home.

Model number UX0918 - September / 2009

here's a list of parafocal lenses:

Parfocality - Canon sez: Canon SLR Lens Talk Forum: Digital Photography Review

note this is from 2004

Thanks Don, So it is apparently Parafocal.

It's the free play that seems to be an issue, wish I had another to test. Should have gone with the f4 or the Sigma!

This worried me at first because so many still zooms are not parfocal, but I've found I don't miss it much - instead of zooming with the lens you just use the camera's zoom function and it works just as well.

Evan, I didn't notice at first because it focuses so well by hand live. It's only when I was trying to get a handle on it's limits on legs I noticed it.

I just find I automatically zoom in to focus. If it like this on another copy, I'll just have to treat her like a prime.