Originally posted by cpk ...as I recall, their website said that spot metering was unusable as a result. At the least, you should run tests before counting on the spot meter readings.
Yep...one of the reasons the effect of split-image screen on spot metering is well-documented and long-known. Canon and other makers that offer spot metering cameras with split-image screens as an option caution strongly regarding the effect of the split image on accuracy of spot metering. KatzEye evaluated their screen on the K-7 and found that metering was not effected except for lenses having maximum apertures* f/2.8 and narrower.
1 Actual bias was as follows:
f/2.8 -0.6 EV
f/4.0 -1.5 EV
f/5.6 -2.5 EV
Note that the KatzEye "Plus" prism was designed to resist blackout to about f/11. Other screens may bias spot metering to a greater extent. As a result, it is probably a good idea to not expect to be using spot metering after installing a split-image screen.
Steve
* One would expect similar with stop-down metering to f/2.8 and narrower.
1 Pentax K-3 K-5, K-5II, K-7, K-30, K-50 & K-500 KatzEye Focusing Screen