according to photozone tests, 40 is sharper. But you'll find many happy owners of 21 too. I would be nice to have both to be honest, just shame 21 is not f2.8 too, I wouldn't hesitate a second to purchase one, but as it is I'm after FA*24 or FA20/2.8 both are scary rare and expensive
I'd love Pentax to bring out new DA24/2.8, and it wouldn't even have to be pancake.... OMG, sorry for the rant...
yes, 40 shoudl be sharper, but then 21 lets you see a whole lot more from the world, and supposedly both are doing very well in resistin flare...
but I onlo own 40 so what do I know
BR