LOL using D200, shouldn't shoot F18..
should shoot max of F11.
Reason given below. You'll suffer significant loss of details at F18.
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
enivre, do you mind shooting directly perpendicular to a piece of paper with words, using 1:1, and post results? I went down to CP today, and tested their only copy left (nikon mount) using their store D70s. Don't know if it's me, but the corner sharpness seems to be rather bad wide open.
Below are just my impressions when I went to test which mid length macro lens I wanna get. LOL was like 90% sure of buying the tokina 100mm liaoz, but CP ran out of canon mount, only left 1 at marina side, so i had to test their nikon mount version.
Tokina 100mm @ CP: took and kept 2 images, both images corners are soft. Focus ring VERY tight. Build is fantastic. Feels like a chunk of light weight metal. dunno how to say, but very detailed stepping for macro wise focusing => think you can finetune focusing for distances less than 1m alot more than from 1m to infinity. That takes damn long for AF from macro distance to normal shooting distance. AF is quite accurate at both normal and macro distances. Missed once when i was testing focusing from close distance to far distance to close etc. The limiter doesn't give a very reassuring lock/click for me to know that it's working.
The tamron 90mm @ CP was surprisingly very sharp from corner to corner wide open. Very accurate AF at macro distances. When using as a normal telephoto lens, focus can keep missing and missing and missing. Wow.. this lens LOOKs like the tokina 100mm. Even the limiter looks the same, and works the same.
The canon 100mm USM @ CP seem to be soft. USM is fast and silent, BUT it is definitely significantly slower other USM lenses that I've used. the AF DOES miss a bit at macro distances. from near to far to near to far, focus is super snappy. missed once. Anyway I think I'll wanna go back retest, perhaps @ TCW instead. The images are surprisingly soft. Not consistent with the prev 100mm usm that I've used before *scratch head*
the canon 100mm no USM @ TCW is rather sharp, consistent from corner to corner. Focusing is loud, but quite snappy. Makes me wonder if the lens is on drugs. I don't remember the previous 100mm I've used before being so loud and fast. Even with the limiter on, at macro distances it kept missing for a while until i changed an object (from box barcode to my CF card).