Goincarcrazy said:
The precision matte focusing screens, although dark with this lens, REALLY help with focusing.
It was my understanding that the benefit of the precision matte focusing screen is really for lenses faster than f/2.8, since the laser etching on the standard screen which is intended to brighten slow (e.g. consumer) lenses limits faster lenses to VF brightness equivalent to about f/2.5. I've certainly confirmed that with my 85L and a standard screen, where stopping down from f/1.2 onwards with DoF preview, the VF does not get any dimmer until I hit ~f/2.5 (although on my 7D, it's clear that the light is getting in since the transmissive LCD in the VF is much more 'washed out' at f/1.2 than f/2.5, even though the scene brightness is unchanged).
Since the 'brightness' of the VF changes in tandem with the DoF seen through the VF, the standard focusing screen is showing you a DoF equivalent to ~f/2.5, even with a wider aperture lens. Thus, precision focusing screens are better for fast lenses because they are showing you the true DoF at apertures faster than f/2.8.
However, I was not aware that there was a significant benefit to the precision matte focusing screens with for manual focusing with f/2.8 (like the MP-E 65mm) and slower lenses. I could see the benefit of a split screen and microprism, but not sure about the benefit from the plain matte screen. Can you elaborate?
