T3i with a EF 100-400mm f/4.5-5.6L. Focus problems

[Antonrides]

Hi I have a canon T3i and just bought a EF 100-400mm f/4.5-5.6L. But mt photos just don't seem as if they are very sharp or focus. I took a photo of a snow owl and the ones with my 55-250mm actually turned out better! I was shooting at a shutter speed of 640 and 1000. Any suggestion

[cicopo]

Technique has a lot to do with using a long (& heavy) lens. Test using a tripod & shutter release cable or the timer before blaming the lens.Also (doubt it applies to the Snowy Owl shots) be certain the focus limiter switch fits the situation. 

[ebiggs1]

There is a learning curve with very long tele lenses.

At 400mm on your T3i you are actually trying to use a 640mm lens.

That's not only going to magnify the subject you are shooting but all the errors you may have made.  And at the same ratio!

You are probably looking at a minimun shutter of 1/640.  Making 1/1000 likely the slowest shutter you will get super sharp photos.

Investment in a good tripod is a great addition to your equipment.