Skylight filters were made as a solution to a common problem in film cameras: most films were meant to shoot photos outdoors in natural sunlight, and if you tried to take a photo indoors or even in the shade, the colors would not come out naturally.
One alternative to skylight filters were UV filters, but with modern digital cameras, you can get away without using skylight filters at all. In fact, in most cases, you will be better off without any skylight filters at all.
Why skylight filters used to be important
In some circumstances, photographs would have a blueish tinge which messed up the overall colors of the picture. The blue tinge was caused by blue “cold” light which was present in overcast skies or cloudy skies.
That’s where the name “skylight” came from, since the filters were designed to counteract this issue.
If you were shooting indoors without a filter, you’d get really weird, yellow shades everywhere thanks to tungsten lights!
Skylight filters had an orangeish-pinkish-magenta color which would “warm” up the colors in the photograph, counteracting the “cool” blue light. Filters came in two varieties: 1A and 1B, where 1A had a milder tint and 1B had a more intense tint.
You would simply attach the filter to your camera lens whenever you were in those conditions, and once you were back in sunlight, you could remove the filter and shoot as normal.
Skylight filters were especially useful for film photographers taking nature photographs. If you wanted to photograph a distant mountain, there would be a lot of sky between you and the mountain and all that atmosphere adds a blueish tinge to your photos. The skylight filter helped warm up the color to make it look more natural.
This was a huge advantage, since you could not remove a roll of film until it was fully used up, and there was no way to adjust white balance.
Filters also served as a protective covering on the lens against scratches and bumps.
Should you use skylight filters on digital cameras?
The simple answer is no.
Digital cameras have advanced processing systems which can adjust white balance on the fly. White balance was an issue when films could only handle one kind of light, but digital camera sensors can adjust and compensate for different lighting as you’re taking the photo.
You can also adjust white balance manually, and if you don’t want to fiddle with it while you’re taking the shot, just shoot in RAW and adjust the white balance later.
If anything, using a skylight filter on a digital camera will change the light coming into the digital camera sensor and the camera will no longer be able to properly correct for white balance.
Additional filters also means additional layers of glass, which increases the possibility of flares. Finally, the magenta toned lens can mess up skin tones.
UV filters vs Skylight filters
UV filters are just an extra layer of glass that blocks UV light. Since UV is non-visible light, there’s no tint on UV filters. Skylight filters are the same as UV filters, except they have an orange/magenta tint to them.