Originally posted by fwcetus I think that the Optibrite treatment affects only the matte area of the screen, making it brighter in appearance at smaller apertures (than it would otherwise appear at smaller apertures) -- I do not think it affects the central focusing aids. [Someone please correct me if I am wrong.]
I think that the Optibrite treatment may also exaggerate the metering error a bit more than the standard screen does. [Someone please correct me if I am wrong.]
I ordered mine this time without the Optribrite treatment (partly to same money, and partly to minimize metering errors). Some of my lenses are fast (some MF, some AF), while some of them are slower (some MF, some AF), but I'm not expecting a significant problem with dark screens... [I may be proven wrong, of course.]
Spot metering with any split prism focus screen is unreliable on a DSLR - which is a given - but centre-weighted and matrix metering work just fine with or without Optibrite treated screens. I always chimp the first shots to check and adjust the exposure with exposure compensation regardless of the lens used, the shots following thereafter are mostly consistent.
Optibrite treatment does noticeably increase the brightness of the focus screen over the focus screen without the Optibrite treatment. I was fortunate enough to acquire KatzEye focus screens with Optibrite treatment for both of my Pentax DSLR (K10D, K-5 - K10D already had a KatzEye screen without Optibrite treatment).
Having a brighter focus screen means that whether you use fast lenses or not, you can start shooting earlier in the dawn and finish later into the dusk. And as any photographer knows, truly magical lighting conditions occur in the early dawn or late dusk hours - I am just too lazy to go out and shoot in those wee hours.