went and ckecked out 3 copies of the 100-400L IS this morning.
happy to say that all three are identical.

shots at 100,200,300 all checked out as i expected. 400@f/5.6 looks like what i have been seeing, but please give me your opinion.

all else considered, i was also looking for any back or front focusing and happy to report that at all zoom settings tried, all were dead on (kudos to Canon QC for once).

here is an image i would really like you to see and tell me what you think..........it is at 400mm @f/5.6, converted with RSE (shrpening turned off) and this is through a morning haze.

http://www.pbase.com/image/51062802/original

Please don't take this the wrong way but I have no what it is a picture of; where you focused or what you are asking for an opinion of. If this was a test of the lens's sharpness, it is difficult to discern anything from this particular image.

Looks like what I get at 400...I find if I back it off just a bit it sharpens up some.

I'm still kicking myself that I did not say "I'll take your 300" instead of asking about a partial trade with the 100-400...it went so fast.

What are we supposed to see? It's a crappy photograph of some trees behind an out-of-focus railing, the tree exposure is a bit off, and as you said there's some morning fog...

Com'on, folks, Michael is not trying to show a pleasing picture which you can put on your desktop, he is talking about sharpness. There are many details in the tree, and I think it's fairly sharp for a wide open shot.

EXIF said JPEG 6 (6 out of 10). Isn't that a low quality image to start with?
Historically the 100-400 zoom is said to be somewhat soft at 400mm, wide open. Also sky is hazy.

It doesn't look terribly sharp, but the 100-400 is softest at 400mm, and f/5.6 is not its best aperture. By coincidence, I tested my own 100-400 about an hour ago, as a result of two test reports.

Photozone shows the maximum sharpness at f/8.0; whereas luminous-landscape shows maximum sharpness at f/11.

My crude test indicates that my lens may be slightly sharper at f/8.

Many pros are saying that they are getting better sharpness by converting in DPP 2.03 than in ACR. I don't know how they compare to RSE. If you try DPP, try the sharpness slider on the RAW tab at 3 or 4. It may depend on which camera you use.

Based upon the conditions presented, the depth of field at the distance the photo was taken, and the compression of the uploaded file, I'd say the tree bark is as sharp as you might expect at 400mm from this lens in this type of situation, with the file prepared in this manner.

It would improve a bit with much better light, but it still is not bad at all. Depth of field at 400mm from this distance is slim, so don't expect more than the center section of the tree to be ideally sharp.

thx, yeah i know it is a total crap example..........was in a hurry between going down and sampling and then picking the one where i felt should have been even crappier..........i'll take some better shots this weekend to share.
man, from 100-300 though, this thing is like a prime even wide open.

Even at 400 it will be like a prime, once you get the hang of it. Takes some time to master, but it is a worthy lens.

composistion you say..... yeah bad example.....i guess i was just wondering if the amount of detail in the trees bark is up to snuff.

i didn't know posting a simple sample for opinions of captured detail could be so difficult for some to understand.

I honestly don't think it looks that bad for 400 w/o.

spartan