Canon EF 70-300 Lens - Jumpy

[dgaver]

I am new to digital photography and purchased a Canon EF 70-300/4-5.6 IS USM telephoto lens for a EOS 7d.

When I push the shutter button down approximately 1/2 way the lens will sometimes struggle for focus, it seems to jump around.  If I push the shutter button down a bit further it seems to work. 

Is this typical of this lense or did I get a defective lense.  The other lens that I have does not do this, kit lense 28-135.

Thanks for the help.

[KeithB]

Is it the focus that is jumpy or the IS?  In bright light I have not seen any focus issues, it does tend to hunt a bit in dim light though.  The IS is jumpier on my 17-85 than my 70-300.

[jamisan]

mine does that sometimes mostly it is just "hunting" for a focus. you might want to check where your auto focus points are set. also you need to remember the min focus on that lens is around 4 feet

[dgaver]

Thanks for the responses.  Keith, it is the focus that is doing this.  It was in a low light situation (high school football game, under the lights).

[KeithB]

For those kind of situations it might be best to lock focus to the center point to make sure you are focusing on something.