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) woman may be fitted with a larger size diaphragm when she is near ovulation. The correct size for a woman is the largest size that she can wear comfortably throughout her cycle. In the United States, diaphragms are available by prescription only. Many other countries do not require prescriptions. The spring in the rim of the diaphragm forms a seal against the vaginal walls. The diaphragm covers the cervix, and physically prevents sperm from entering the uterus through the os. Traditionally, the diaphragm has been used with spermicide, and it is widely believed the spermicide significantly increases the effectiveness of