UV filters are used primarily for lens protection and haze reduction and are also to impart a warm tone in some cases.
About UV Filters
UV filters block ultraviolent (UV) radiation but usually allow all of the visible spectrum of light to pass through. Some UV filters also block a portion of visible violet light.
UV filters are used for three main purposes. The first is lens protection. UV filters cover the lens and protect against damage that could be caused to the lens. This includes scratching and cracking from dropping the camera, scratches obtained from dust, debris and sand that may fly into the lens, and moisture from condensation, humidity, and rain.
There are arguments for and against the use of UV filters when it comes to protection. Proponents for using them cite the expense of replacing damaged lenses against purchasing relatively cheap filters. They also provide an element of convenience. However, UV filters can affect image quality, partly because of aberrations which can cause blurring, but also because the extra air to glass interfaces cause flare, manifesting as haze or starbursts across the image. The extra surfaces may also become scratched or smeared. Additionally, UV filters can affect autofocus mechanisms and the attachment of lens hoods.
The second purpose is to reduce haze. Haze is caused by dust particles reflecting light. Haze effects from UV light reflections can produce more noticeable effects than others in photographic images because UV wavelengths are shorter than other wavelengths. The image may look less sharp, with a hazy bluish appearance. Using a UV filter can make the image sharper and remove the bluish tinge.
The third main purpose of UV filters is to impart a warm tone. Strong UV filters are used for this. They also block a portion of violet light in the visible spectrum. This type of UV filter has a pale yellowish colour. They are even better at minimising the effects of haze and can result in a warmer toned image, with brighter and richer colours.
Choosing a UV Filter
Choosing a UV filter involves considerations about what it is to be used for and where. UV filters vary in their quality, strength, method of attachment and materials.
Some of the problems mentioned above can be minimised or avoided by choosing a good quality UV filter. Good-quality filters may not affect factors such as the autofocus or attachment of lens hoods in the same way as lower-quality UV filters. Good-quality filters will be more precisely made to be as flat as possible and made with higher-quality materials. Coatings applied to the filter will reduce or cut out flare although this also slightly lessens the amount of light that can pass through. Look out for multi-coated filters which are more effective at cutting out flare.
UV filters are available in different strengths. Those that just block UV light are clear. They are used for protection and minimising mild to moderate haze. Stronger UV filters are used for protection and are more effective at reducing haze. These have a pale yellowish colour and can also be used to warm images.
Skylight filters are another type of UV filter. They are pinkish and can also be used to produce a warmer effect.
Method of Attachment
Camera filters are available in several types, referring to the method in which they attach to the lens. Screw-in filters are the most frequently used, and for UV filters which have a protective function, they are the most convenient and effective. The circular filters are simply screwed into the lens. This does mean they need to be the same size as the lens, so check the size of the lens before purchasing a filter. It also means that additional filters may need to be purchased for each lens. Standard sizes include 52 mm, 58 mm, 62 mm, 67 mm, and other sizes.
Filter systems use a filter holder mounted to the front of the lens. Filter holders are available in different shapes and sizes. This means that they can be used with different-sized lenses, which is a big advantage in terms of budget and convenience. However, they are not as effective at providing protection as screw-in filters. Filter systems can often be used with several brands and models of camera, but others are more specific, so always check it is compatible before purchasing.
Filter rings, or step up rings, can be used for different-sized lenses. They are useful for when UV filters are used to minimise haze though not so much for protective purposes. Buy the filter to fit the largest lens and then use filter rings to attach the filter to smaller lenses.
There are also drop in filters for telephoto lenses with the appropriate attachment at the rear of the lens.
Both screw-in filters and filter systems are usually designed so that more than one filter can be used at a time. This means that UV lenses can be used alongside other filters and do not need to be removed to change filters. Bear in mind that additional filters mean additional air to glass interfaces which may affect image quality.
Another consideration is whether to purchase glass or optical resin filters. Glass filters are more expensive but often of better quality, having less impact on image quality. Resin filters are more lightweight and usually cheaper but are also more prone to scratching.
Both glass and resin filters can be fairly long lived, providing they are handled carefully and properly maintained. Because filters can be difficult to clean, it is important to keep them as clean as possible, avoid touching the surface when handling them, and keep them properly stored in filter wallets when not using them. It is also possible to lubricate the thread on screw-in filters. Always check guidelines provided by the manufacturer, and follow their instructions with regards to cleaning and maintenance. This will ensure the filter stays in good condition, providing better-quality images for longer.
UV filters block UV light. They are used for three main purposes – lens protection, haze minimisation and warmth. With regards to protection, UV filters can protect the lens against dust, debris, moisture and damage from dropping. Most filters used for this purpose are screw-in filters. Arguments for their use include the expense of replacing damaged lenses, while arguments against include a loss of image quality, particularly with lower quality filters. When it comes to minimising haze and producing sharper images, all UV filters can do this to an extent but stronger filters, which also block a part of the violet spectrum, are more effective. Stronger UV filters can also impart a warm tone to the image.
Choosing a UV filter involves considerations about its quality, strength, method of attachment and materials. Potential issues with image quality can be solved by using a good quality filter, which is more precisely made and has multiple coatings to cut out flare. The strength of a UV filter can indicate how well it can reduce haze and warm images. While screw-in filters are the most frequently used, other UV filters include filter systems and drop in systems for telephoto lenses. Filter systems have the advantage that the same filter can be used for different-sized lenses, whereas screw-in filters need to be the same size. UV filters are available in both glass and optical resin. Glass filters are more expensive, but resin filters are lighter and easier to handle. Whichever type of filter it is, always handle it carefully and store it properly when not in use. This will keep the filter in optimum condition for longer.