(in Japanese, Google English Translation Here)
Actually, this is a dual 7-blade aperture mechanism, instead of one that is composed of 14, so as to save manufacturing cost. The problem of a traditional 7/8-blade "circular" diaphragm design is that the aperture opening is not always in form of a circle, i.e., at different f-stops the shape may be deformed a bit, thus the new patent.
"Round" Lens Diaphragm? See This! :-o
Thursday, July 19, 2012
New Pentax Circular Lens Aperture Patent