Diaphragm (optics) bright spots, for example night cityscapes. Some cameras, such as the Olympus XA or lenses such as the MC Zenitar-ME1, however, use a two-bladed diaphragm with right-angle blades creating a square aperture. Similarly, out-of-focus points of light (circles of confusion) appear as polygons with the same number of sides as the aperture has blades. If the blurred light is circular, then it can be inferred that the aperture is either round or the image was shot "wide-open" (with the blades recessed into the sides of the lens, allowing the interior edge of the lens barrel to effectively become the iris).
Diaphragm (birth control) to test whether the diaphragm offers protection from HIV found that women provided with both male condoms and a diaphragm experienced the same rate of HIV infection as women provided with male condoms alone. Because pelvic inflammatory disease (PID) is caused by certain STIs, diaphragms may lower the risk of PID. Cervical barriers may also protect against human papillomavirus (HPV), the virus that causes cervical cancer, although the protection appears to be due to the spermicide used with diaphragms and not the barrier itself. Diaphragms are also considered a good candidate as a delivery method for microbicides (preparations that, used