Take two sample shots with and without the filter. The following were two I took for testing the lens fully open at 400mm. They are 100% crops of an area. I thought it was soft until I removed the filter! The link above is to my post on Photography on the Net I posted yesterday!
Try opening up the pix in the Canon zoombrowser that comes with the camera. It will let you see what focus points have been triggered.
I like your thinking, but I don't think you could conclude much simply from the Zoombrowser highlighting of the chosen focus point. What if the shot was focused and then reframed, or if focus was set and then the bird moved a bit. Wez uses the "*" button for focus so it would be quite possible, in any focus mode, to set focus and then have the bird or the camera move somewhere entirely different.I really wanted you to try it to see if your aim with the centre focus point was accurate.
Wez,
If that little house is completely unsharpened then I think the result is not that bad. The antialiasing filter is going to introduce some softness and raw files need some sharpening just to combat that, never mind making up for any deficiencies in the focus accuracy or sharpness of the lens. I do think sometimes there is a real danger of pixel peeping ruining people's enjoyment of their photos.
My robin was at 400mm full zoom and unsharpened so I'd say that's still a little soft, although a couple of times with my lens I've had this. Have you got the focus distance set appropriately, which IS mode (or IS off?)
Anyone nearby to borrow a lens from or local photo shop for a comparison?
But is your robin image a 100% crop?
Sounds like user error to me. Long lenses need good technique. Don't depend on your IS, just act like it's not there and you'll nail it next time! Still keep your shutterspeed high enough like there's no IS and use good technique. In time you'll learn how to use your lens and you'll be able to bag more photos with slower shutterspeeds.
I personally only shoot with the lens tripod mounted, with mirror lock-up and remote shutter release. But again I don't have IS and my wildlife lens is double the weight of the 100-400, which would be really tiring to use hand held for extended periods of time, but still, at high magnifications and at long focal lengths, the slightest movement is magnified. You may say that the 100-400 has IS, but still, it doesn't perform miracles, you need to use proper technique.
What I would personally like to see as a sharpness test is some text printed (maybe from a book or just something from your printer), set across your lens and shoot at different apertures, at different focal lengths, different distances. Crop a 100x100 pixel from the center for every photo and post here. What we are really interested is its performance wide open, but it's still useful to see how it performs a bit stopped down.