Lens Filters

Filters for analogue and digital photography

There’s a very large selection out there of lens filters. Conventional analogue lens filters are screwed onto the front of the lens. These correctional and effect filters are used for a wide variety of purposes. In the day and age of digital photography, some filters can even be digitalised and be integrated in the camera. This is a huge advantage for the photographer since he/she then doesn’t have to carry around as much equipment as in the days of analogue cameras. There are still, on the other hand, physical filters that are indispensible even in digital photography. Effects produced by these filters are not currently reproducible with modern photo-editing software. Here, we’ll briefly introduce you to the most common filters:

Polarisation filter

Light is the portion of electromagnetic radiation visible to humans. When this hits a surface, part of this radiation is absorbed and the other part reflected. This reflection plays an important role in photography. With so-called polarisation filters, you can prevent disturbing reflected light (such as glare) from becoming a problem. A polarisation filter is mounted on the front of the lens and absorbs complementary polarised light. The strength of the filter’s effect can be adjusted by rotating the filter on the lens. The filter shouldn’t be rotated more than 90°, however, since this will cancel out the effect. The absorbed light is converted into heat. Thus, the filter will become warmer over time. Besides reducing reflections and glare, using a polarisation filter raises the contrast and colour saturation, which is why they’re especially suitable for landscape photography.

When using photo-editing software, retouching reflections and glare cannot always be adjusted equivalently. This makes the polarisation filter a popular addition to the camera bag, even for digital photographers.

Neutral density filter

The neutral density filter (ND filter), in photography, is an optical instrument. They are made out of either glass or plastic discs and are used to darken an image and maintain natural colour reproduction.

Too much sunshine can overwhelm the exposure latitude of a digital camera or analogue film. In order to reduce the light flow, a small aperture can be selected, which will thereby increase the depth of field. When using an ND filter, you can also use a large aperture even in a lot of sunlight without the image becoming overexposed and thus keep the subject in focus and the background out of focus.

In architectural photography, this filter can be used with a long exposure time which will prevent traffic and pedestrians from appearing in the image.

Other effects that can be made by using an ND filter are the silky smooth appearance of flowing water (such as a flowing waterfall) or continuous light trails from moving cars.

Grey grad filter

This effect filter has a colour gradient from dark to transparent. This filter allows different amounts of light through the lens to the photo sensor or film. You can adjust the amount of dimming depending on how strong you would like to make the effect. The gradient from dark to transparent can be designed to be hard or soft. With a bit of practice you’ll be able to take great landscape shots with the grey grad filter. For example, you might take a photo with a much higher level of brightness at the top of the image in relation to the bottom. In order to correct this, the grey grad filter evens out the exposure difference between brighter and darker areas of a photo, which brings the contrast closer together and makes the photo appear more harmonious.

UV filter

These filters block out ultraviolet light. They’re either colourless or have a slight yellow tinge. Essentially, these filters have two useful properties.

Due to aberrations of optical lenses (chromatic aberration), blurriness in the image can appear because of a high proportion of UV light. This leads to light scattering on molecules in the air to a maximum intensity in the UV range (Rayleigh scattering) and produces a blue tint in the image. Digital cameras can counteract this with an automatic white balance. In multi-lens objectives found in modern cameras, UV light is already filtered and using a UV filter isn’t necessary. Some photographers use a UV filter to protect lenses against scratches. This is not recommended, however, since the filter can break easily, which can damage the lens itself.