please help to understand the lens issue

[mukul]

An used 70-200mm-f-4L-IS is on sale, but the sellers mentions the following problem.
I could not quite get that. Can you please explain the following issue?


"I recently realized that there is a known flaw known as Focus Slipping in this line of canon lenses and unfortunately this unit is also affected by it. The focus goes from 1.2 meters to infinity smoothly but does not turn back from there while in manual focus. In auto focus it moves both ways but is sluggish while going from 3 meters to 1.2 meters. It achieves perfect focus from 1.5 meters to infinity. For this reason I'm pricing this lens at a low price, it's still a functional lens with a semi-functional focus system. The lens came in like this from Canon so this issue was not caused by any mishandling on my part, unfortunately I realized it a bit too late to get it fixed under warranty, in fact I found out about it only when I decided to sell the lens. This is an As Is sale with no returns as I have shared everything there is to know about this lens."

http://www.ebay.in/itm/CANON-EF-70-200mm-f-4L-IS-USM-LENS-/261699401367?pt=IN_SLR_Camera_Lenses_Optics&hash=item3cee7ff697

 

[wsheldon]

Here's a video illustrating the issue: https://www.youtube.com/watch?v=uI15shZyn9Q

Fortunately mine (~4-5 years old) does not exhibit this issue. Looks annoying and certainly something I'd have fixed (and would avoid in a used lens purchase).

 

[Khalai]

I had mine repaired twice with this phenomenon. After second repair, I sold it for a low price and the buyer was fully aware of the issue. Really a shame, non-IS version of mine never showed such issue, only IS unit seems to affected by that.