Does anyone know why there are 4 different types of H screens?
Allegedly they correspond to four different maximum lens apertures.
I don't see why that is necessary with a camera system where the light
metering is not in EVs.
The angles that the focusing prisms are cut at on a focusing screen are
always a compromise. The wider the angle, the faster the focusing, but
the sooner they black out (one of both sides becomes totally dark and
useless). Most screens are compromised to black out at about f/5.6.
The H and G (I think) screens have the prism angles matched to certain
lenses and apertures, to give as much as to focusing aid possible
without blacking out.
This is a little used but great advantage for the Nikon system,
especially with long MF telephoto lenses. Most other systems do not have
these matched screens available.
Colin
