Originally posted by twitch I thought the problem with the DA14 was field curvature in close & lack of sharpness at infinity focus?
The sharpness of this lens is actually decent at any distance when in focus. The problem is field curvature at normal shooting distance. When the centre hits infinity, the focus of both sides is much closer. When both sides hit infinity, the centre goes beyond. The work around is to let the centre goes beyond infinity and stop down to f11. This way, the whole frame is reasonably sharp, but never as sharp as "in focus". At least 2 of my 3 copies (didn't test the 1st one I had) behave this way so it's probably part of the design. At closeup distance, it doesn't suffer much.
I tested my 3rd and current copy against a wall at less a metre. As you can see from the full size picture below, all 4 tips are sharp, so is the centre. However, the highlighted porton is a little blurry. This is inline with the mustache distortion and the severe field curvature that I have experienced.
http://www.pbase.com/wlachan/image/136349622/original.jpg