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. "Contraceptive Technology" reports that the method failure rate of the diaphragm with spermicide is 6% per year. The actual pregnancy rates among diaphragm users vary depending on the population being studied, with yearly rates of 10% to 39% being reported. Unlike some other cervical barriers, the effectiveness of the diaphragm is the same for women who have given birth as for those who have not. The diaphragm does not interfere with a woman's natural cycle, therefore, no reversal or wait time is necessary, if contraception is no longer wanted or needed. The diaphragm only has to be used