It has been some time since I pulled out the 400mm lens to take a few shots.
A number of years ago, I bought the 400mm Canon "L" Prime lens,  F 5.6.
I bought it because I am one of those nutz that likes SHARP images.  I don't really care for "pretty sharp" or acceptable, not too bad...
I like sharp lenses.
As you know, some are, and some are not, and some are only sharp at certain F stops.
I have one of those too, a 28-135 (not an L lens) that is soft until I stop down to 6.3 to 8.0.
I love that lens, but not wider than F 6.3.

I have a couple more; a 17-40 "L", very sharp, and a 70-200 "L" not so sharp, and the old old, 50mm, very sharp.

But let's get back to the 400 that I pulled out of my bag again.
I have a good tripod, and a very good head, and..... I use a CABLE RELEASE with this lens.
"A Cable release?   Yepper!
I am either a klutz, or heavy handed. I am not sure which, but the snap of the shutter button when I shoot will soften the shot.

Got this one the other day... not sharpened, right out of the camera except for a crop.

Just wanted to share lens stories, and hope you will share some back.
Remember to click on the images to enlarge.

Fred

A couple of years ago I got a Sigma DC 17-70mm macro HSM

I did a rather crude test at various apertures and F'lenghts and was not all that impressed with the results at the 17 and 70 range and F3.5 and F32

Took some shots in the Tate Gallery last week in the range  17mm f3.5 30th 400iso (lowish light hand held) and they are noisy and not sharp enough.

That effort and you have spurred me on to do a better test.

jeff