How UV-Filters may Damage Your Photographs
Often UV-Filters and similar (Sky, 1A, KR1, etc) are used for pure protection purposes only. Whether a filter is capable of protecting a lens at all is questionable and heavily discussed in the web. This article, however, focusses on the cost of this questionable protection - the damage that filters can do to your actual photography.
This kind of arrebation is always there when you use an UV filter for whatever purpose, although it is significant and clearly visible on night shots and other situations with very high contrasts. While collecting these example photographs I got a studio photography with two women in front of an illuminated white background. The girl's silhouette was visible in each other's faces caused by the same phenomenon that I am presenting here. Unfortunately one of these ladies did not agree to publishing the photograph in this context. That I have to respect.
For a start I show you the effects that Axel observed when he photographed some firework with a filter as protection.
Willy Brüchle's comparison of the same night shot with and without his filter is nearly a classic in the German forums.
It git a bit more obvious when we asked her to show the full frame.
Just for demonstration purposes I turn the picture into its inverse. The lights are dark here and can clearly be seen and matched.
Mirrorings caused by filters are often mirrored symmetrical along the optical axis - the centre of the image. When you now link the mirrorings with their corresponding lights causing them then the lines will cross each other in the centre of the image.
Contrast and Brilliance
I did not even mention the impact of a filter on brilliance and contrast of the image for normal photographs. The reason for that may well be that people do not notice it because it is not that obvious and easily fixed in the age of digital post processing. And of course I don't have any of those examples myself because I do not use protection filters myself. Well, it is about time to produce some with- and without-example.
This topic is often discussed in the context of UV filters, but it must not be overlooked that the problem can occur with every filter. Every filter adds a pane of glass to the optical system that may have these unwanted effects.
The following image of the Yeldize in Dresden from Marcel Hermann shows exactly this effect. Marcel aimed to turn the lights into stars and therefore added some star effects filter but the filter did not just add the star shape but caused unwanted reflections too.
If you really want to protect your lens with a filter instead of the lens hood and lens cap (the devices made for protection) then feel free doing so, but don't complain with me about the consequences.