The Katz Eye™ focusing screen for the Nikon D40 & D40x
is a laser matte with a split prism circle and a microprism
collar, very similar to the one you’d find in many classic SLRs.
Details Here
Flickr disscusions on Katz Eye
OR
FocusingScreen.com here
Comments:
Recently installed mine and it helps a lot with focusing a 50mm 1.8.
Haven't noticed any difference in metering.
The Katz Eye site claimed that the screen darkens at smaller openings - this is true however it seems darker on dx lenses than non-dx lenses on the same opening
It's good fun especially with non af-s lenses.