Originally posted by jwmster So Doglover, thanks! But if I may follow up: S-type will NOT affect exposure, right? Are you using plain S-type, or S-type with Grid, with A-frame, (or both of the latter)?
An S-type screen can actually improve the accuracy of the meter at smaller apertures.
A stock Pentax screen it is actually brighter at smaller apertures than it should be, this isn't really a problem with modern lenses as they meter wide open and there aren't any slower than about f6.3. Where it becomes a problem is with lenses that don't have A contacts, these can't meter wide open unless you are actually wide open. So when you are shooting at f8 or f11 the lens must be at that aperture to actually meter.
The S-type screen is almost perfectly linear, so the meter sees the true amount of light regardless of aperture. This has a downside though, if you shoot M42 lenses at small apertures it can actually be even harder to focus.
The split prism screens like the Katzeye won't affect center weighted or matrix metering that much, just spot metering.