Originally posted by Kozlok The 40 is sharp at any aperture. It is sharp-er at 5.6, but already pretty amazing at 2.8.
Optyczne, the original Polish version of Lenstip, disagreed
(and also cast doubt on the Photozone review quoted earlier).
After praising the central resolution, they wrote that
"It's a completely different situation at the edge of the frame.
Around fully open, we have a situation which may well be called weak.
To reach decent levels [MTF50 of at least 30 lp/mm on the K10D],
we have to close the lens down around two stops."
Test Pentax smc DA 40 mm f/2.8 Limited - Rozdzielczo
Strangely enough, this review does not seem to appear in an English version on Lenstip.