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What is an Ultraviolet (UV) Filter?
They are used to filter/reduce the level of Ultra Violet rays getting through to the camera sensor. They are transparent to the visible light.
Earlier photographic films were sensitive to ultra violet light but nowadays the digital image sensors are insensitive. Many photographers would therefore conclude that there is no point of using UV filter on modern digital cameras
UV filter are cheaper compared to Polarizing filters and can also be used to protect the lens from damage when shooting since they are transparent and have ‘minimal’ effect on the exposure of the image.
This minimal effect is a disadvantage to you as the photographer since you want to shoot a perfect image as possible. This is because a UV filter will add another layer of glass on the lens which means the lens is not perfectly flat which leads to reduction of sharpness on the image. Another disadvantage of having another layer of glass is because it results in reflection of light which will result in flare.
So mostly you will use the UV filters for protecting your lens. But you should not depend on UV filters to protect your lens when storing your camera; the best way to protect your lens when moving around or inside the camera bag is to use the camera equipment i.e. lens cap. If the filter itself gets scratches it means it needs to be replaced.
So now the question is whether you need this filter at all; I would say YES, the protective properties of a UV filter is still justified mostly depending on how you use the camera, I have different experiences with camera lenses as photography trainer with students manhandling the equipment, losing the lens caps, wiping the dust off the lens with their handkerchiefs, touching the lens with greasy fingers and even accidentally whacking the lens on a wall.
If you operate your camera in an environment with very high risk of damage and scratches then you might consider using the UV filters for protection. It may also depend on the type of photography you do e.g. Desert photography exposes your lens to more dust and sea photography with moisture.
Another advantage of using the UV filter would be to avoid the wear and tear of the lens when cleaning it. When you use the filter you will hardly clean your lenses and this prevents the wear brought about by regular cleaning which can lead to reduction in the sharpness of the lens. The UV filters are not very expensive compared to the price you would pay to get a new lens.
UV filters come with different price range depending on the quality of the filter e.g. the thinness of the glass, the coating specifications. Some filters have addition coating apart from the normal coating which is designed to reduce the flare. This coating may also help in maintaining the original colour contrast of your scene. They also have little effect on the exposure level which makes them more favourable.
When it comes to the thickness of your UV filter always remember the thinner the filter better the quality of your image. Firstly, this is because the thin filter will transmit most light hence no reduction on the exposure of your image. Secondly, a thicker glass risk reflecting more light which in turn reduces the sharpness of your image. The UV filters may also come in form of gels, though they are fragile than glass in preventing your lens, they are very thin which makes them desirable due to minimal effect they have on the image exposure quality.