Coloured photographic lens filter test for digital cameras

By Matt Cornock

If you’ve ever wondered what the effect of coloured filters has on photos taken by digital cameras, well wonder no more. I recently purchased a cheap set of colour solid and graduated filters and decided it was time to run a little experiment. See the results here:

A little bit of explanation

Filters are used to block out certain colours of light, or reduce the overall light intensity coming into the lens of a camera. Often ‘neutral density’ filters are used to block light, allowing for longer shutter speeds to blur moving objects or soften water shots. Coloured filters can also be used to emphasise different characteristics of an image, usually when captured or post-processed in black and white. The comparison page I have created shows this to great effect when we look at the red, green and blue components of an image (an easy editing process using a ‘channel mixer’ tool).

For example, taking an image with a red filter will block a bit of green and nearly all blue light. When extracting the green and blue channels, they appear significantly darker than the red, showing different levels of detail. The straight equal-channel greyscale mix emphasises clouds in the blue sky, as the clouds are white (an equal mix of all channels) but the sky is blue (blocked by the red filter, turns it much darker than natural).

Filters have lost favour in digital photography because some people believe all effects can be created in the editing programme. However, digital cameras are limited in the range of light and dark (their dynamic range) and this can mean over-exposed skies or under-exposed foregrounds. Filters, particularly graduated ones, can help redress an exposure imbalance – something that can only be done before the light hits the sensor. Again, the comparison page has examples of this.


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