learning curve to the 70-200?

heyya POTN,

I've had my 70-200 2.8L for about 3 or so weeks, and I havent really gotten out to using it until lately.

Yesterday I tried shooting with just the 70-200 on my camera and the results I see are kinda confusing. I dont know if the lens is backfocusing, or if its just that shooting at f2.8 provides you with such little margin of error.

I have attached two pics, exif intact. Both were from my xti w/ center focus enabled.

In the first picture it looks kind of like back focusing. Granted I dont have IS, I could have accidentally focused on the cars in the back thinking i had focused on the car itself, then shot it. Thus throwing it off, but I'm not too sure this is the case.

The second picture seems fine to me, it was shot at f4. (probably should have shot it at 2.8 for comparison purposes)

So is what im experiencing most likely user error? Or is there something wrong with the lens?

Thanks!

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Put it on a tripod or a table and try focusing.

User error.

The first pic is focussed on the black truck. The focus area in your camera is actually bigger than the little square in the viewfinder, and in this case it preferred the truck over the silver car. Presumably the AF line did not exactly overlay anything high contrast on the car and did on the truck, so it went for that.

Also remember that the little squares only approximate where the actual AF sensor is. It might be high, low or shifted a little left or right of the marked square. If your's was high - left it would almost certainly have gone for the truck.

With a sharp edged target and a tripod you can actually map out where your sensor is.

thanks guys as long as its not the lens im not worried!

Have a look at the on line DOF (http://www.dofmaster.c​om/dofjs.html)calculat​or-at 20ft f2.8 and 140mm if I read it correctly your DOF is not a lot about 6 inches ( 0.65 ft)

offtopic : http://www.dofmaster.c​om/dofjs.html , very intersting link , thanks troutfisher