http://egami.blog.so-net.ne.jp/2012-07-18(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
