This UV Filter blocks the invisible UV component of light from the sky, which can cause blur and to which many color films react with a blue cast. These filters should be called UV-Blocking Filters, because there are filters for technical applications that pass UV radiation and block all the other wavelengths. Nevertheless, the short term UV Filter has become established among photographers. UV Filters are ideal for photography in high altitudes (in the mountains), by the sea and in regions with very clean air. The pictures gain brilliance and disturbing blue casts are avoided. Because the glass is colorless, color rendition is not altered, aside from the elimination of the unwanted blue cast, and no increase in exposure is required. That makes a UV Filter very suitable as protection of the front element of the taking lens against dust, flying sand, sea water spray and the like, and it can be kept on the lens at all times. It is recommended for analog color and black-and-white as well as digital photography.
This is the size of a front lens cap. Standard sizes for snap-on lens caps include: 27mm, 28mm, 30mm, 34mm, 37mm, 39mm, 40.5mm, 43mm, 46mm, 49mm, 52mm, 55mm, 58mm, 62mm, 67mm, 72mm, 77mm, 82mm and 86mm.
When placed in the optical path, many filters block a certain amount of light from reaching the lens. Filter factor relates to how much exposure compensation is required in order to adjust for this. Most cameras have TTL metering and will be able to do this automatically.