Open Aperture And Stop-Down Metering Lenses - Pentax MV-1 Manual

OPEN-APERTURE AND STOP-DOWN METERING LENSES
Open-aperture SMC Pentax lenses have
a diaphragm coupling lever © on the back of
the lens which couples with the camera body to
permit open-aperture metering. The ultra
telephotos do not have a diaphragm coupler, so
they must be used with the stop-down metering
system. Use of the Auto-Extension Tube Set K
permits open-aperture metering. Use of other K
Series accessories - standard Extension Tube
Set K, Helicoid Extension Tube K, Auto-Bellows
M and Bellows Unit ffl requires stop-down
metering. Whenever any one of these is used
between the camera body and an SMC Pentax
lens, the stop-down metering system must be
used.