A detailed explanation of how UV lens filters work — a popular choice of filter for many outdoor photographers.
Words by Urth HQ
UV lens filters work by blocking out UV light from your camera lens. To appreciate how UV lens filters function, it helps to understand what UV (ultraviolet) light is.
UV LIGHT EXPLAINED
Light is made up of electromagnetic wavelengths, measured as nanometers (or nm). The spectrum of light visible to humans consists of red, orange, yellow, green, blue, indigo and violet. Mixed together, these create a white light. This usually sits at between 390 to 750 nm on the electromagnetic bandwidth. Ultraviolet light resides above the blue end of the visual spectrum at around 10 to 390 nm, so has a shorter wavelength than visible light.
Although human eyes can’t detect UV light, this isn’t the case for a camera’s sensor. This is especially true if you use a film camera or a digital camera that’s over 10 years old. However, modern digital cameras are now designed to do a good job at handling UV light. But, without a UV lens filter, the quality of your images may still be compromised by this light radiation.
A BLUE CAST
This may be evident if you’ve photographed a scene that looked clear to the naked eye, but on camera, showed a blue-tinged haze. When UV light combines with moisture or dust particles in the air, it becomes diffused or scattered. This creates the blue hue.
As well as a blue cast on your pictures, UV light can degrade image contrast and sharpness, creating a haze. This is especially the case if you take photos outdoors, such as a sunny day at the seaside. Or, at a high altitude, where UV light is stronger. If you shoot images of snow, water or glass, these reflect sunlight. This further magnifies UV levels, creating a hazy effect. Faraway images, such as mountain ranges or cityscapes, are also susceptible to atmospheric haze from UV light. More so if you use longer focal length lenses. This can reduce the amount of detail and sharpness from your images.
Adding a UV lens filter to your camera makes sense if you want to reduce the risk of haze and a blue cast, as the filter blocks out the UV light, which causes these to occur. UV lens filters can, therefore, help to improve the clarity and sharpness of your images.
UV lens filters are made from glass that passes all or nearly all light on the visible spectrum, but blocks UV light at a specific wavelength, typically below 400 nm. You can find various filters according to how much UV light they absorb by percentage and nanometers. For example, Urth sells UV lens filters made from the highest quality optical glass that can transmit up to 99.6% UV light, as well as superior UV reduction of just 0.02% UV light up to 321 nm. As further evidence of exceptional quality, Urth uses two of the leading glass manufacturers in the world, Japan Optics and German SCHOTT B270 glass.
Another advantage of using UV lens filters is that they offer great protection for your camera lens, without adversely affecting colouration, contrast or exposure settings. You can leave a filter on your camera at all times, so that if it becomes exposed to any dirt, dust, grease or scratches, these won’t make any contact with your more valuable lens.
To gain the most benefits from using UV lens filters, always choose a high quality brand. Select a filter that suits the particular environment you’ll be using it in the most.