Add Protection and More Accurate Light
WHAT IT DOES
Ultraviolet or “UV” filters block some UV light from entering the camera lens. In outdoor photographs UV light increase the effect of atmospheric haze making distant subjects, such as mountains, in scenic photos less sharp. Be removing some of the UV light it reduces some atmospheric haze yielding clearer scenic photos.
Most people also us UV filters to protect their lens. Lenses can be expensive and so can repairing them if they get damaged. These filters provide an excellent first line of defense for the front element of the lens. High-quality UV filters can remain on the lens at all times as they have no effect on indoor photos and do not reduce the amount of visible light entering the lens.
HOW IT WORKS
A UV filter has glass that is specially formulated to absorb UV light at a certain wavelength and lower.
UV light that is not blocked by the earth’s atmosphere has wavelengths beginning at 315nm and going up to the visible violet light at the 400nm upper end of the visible spectrum. This light is commonly known as UV-A and not only is it bad for your eyes its bad for your photography. The visible light spectrum runs between 400mn violet and 700nm red. Even though UV light cannon be seen by the human eye it can have a negative impact on photos.
High-quality UV filters are referred to as “Sharp Cut” filter because they begin absorbing over 90% of UV light to passing all visible light in the span of only 20-40 mn. UV filters are rated by where this 90% UV absorption is reached. L39 UV glass absorbs 90% of UV at 390nm and below while L41 UV glass absorbs 90% UV at 410nm. All high-quality filters absorb 98-100% or more of UV within 20nm below their L rating and pass 99% of the light within 20 above their L rating.
Insert UV transmission curve diagram
In addition to the L rating, there are two types of UV filters to consider and which is best depends the environment being use. Normal professional and high-quality UV filters are made glass that has standard optical glass strength and does a good job protecting the lens.
For photography in very harsh environments where the from of the lens is more likely to get damages there are hardened optical glass filters. These filters have glass that is chemically hardened to make it 4x stronger than normal optical glass. These filters are more expensive then their traditional optical glass counterparts.