Diaphragm (optics) curved blades improve the roundness of the iris opening. In a photograph, the number of blades that the iris diaphragm has can be guessed by counting the number of diffraction spikes converging from a light source or bright reflection. For an odd number of blades, there are twice as many spikes as there are blades. In case of an even number of blades, the two spikes per blade will overlap each other, so the number of spikes visible will be the number of blades in the diaphragm used. This is most apparent in pictures taken in the dark with small
Diaphragm (birth control) the diaphragm. Insufficient studies have been conducted to determine effectiveness without spermicide. It is widely taught that additional spermicide must be placed in the vagina if intercourse occurs more than six hours after insertion. However, there has been very little research on how long spermicide remains active within the diaphragm. One study found that spermicidal jelly and creme used in a diaphragm retained its full spermicidal activity for twelve hours after placement of the diaphragm. It has long been recommended that the diaphragm be left in place for at least six or eight hours after intercourse. No studies have been