Has disappointed me

I have the lens can test on my EOS 5D for several weeks. Irritated it took me by its compact design, since it has just about the size of the EF 24-105 L. The image quality I've seen as well, vignetting and fringing I could not see and the distortions are somewhat stronger than the EF 24-105 L, but can be removed by clicking in Lightroom or Photoshop. That it is not 100% sealed against dirt, not just one of the lichstärksten and a due weight to me was previously known has and therefore does not flow negative in my review.

So why only 3 stars? For the following two points I have each deducted a star:
- The tube moves when shooting down of its own accord from. In my copy even extremely light. I tried from a tower, take people on the ground, this was due to the extending tube and the resulting change in focal length almost impossible. This is something I've experienced to this extent only With Cheap lenses.
- The autofocus is too slow. As long as I have time to set up everything at rest (eg for landscapes) there are no problems. But wherever it comes down to speed, if I want to hold a certain facial expression in animals at the zoo, or people at an event, and I have to react quickly, the autofocus needs to focus too long and the image is either out of focus or the magic moment already past. This gave me dirty many beautiful pictures and is the main reason that the lens has me so very disappointed.
These two criticisms I might have even accepted at an inexpensive kit lens, but not with a promise of a high-quality lens with a correspondingly high price.

Speaking of price: new costs the lens currently around 1,200, it is used by dealers for almost get half. If one uses it buys from private higher haircuts are possible. I see in this price declines, a sign that I am not alone with my opinion on the quality of this lens: at an EF 70-200 L I'll never get even a used lens with such high discounts, as this has proven to be of extremely high quality , High discounts have somewhere Whatever their reason.

The lens is not bad, so I forgive yes still 3 stars. If you can live with my criticisms, for it may be just the ticket. But class should look different in my eyes. I was just disappointed the lens and I have separated me away again.