The UV filter is supposed to block ultraviolet rays. This was perhaps important for shooting film but most today’s digital image sensors are not very sensitive to UV. Most of the UV is blocked by the glass in the lens anyway. So often these UV filters are recommended by people as a lens protection mechanism.
At beginning, I bought into this. After all, it costs more to repair a scratched front element than a filter. I have never bumped my lens into anything or gotten a scratch of any significance but the filter really kept the front element particle free. I found myself comfortable wiping down the filter even with my shirt sleeves when I cannot find lens tissue or lens pen. I wouldn’t do that with the lens front element. I know that small scratches will hardly cause any image degradation. However I may have trouble selling my lens with scratches on the front element because not everyone understand this…
Later I realized that any UV filter you put on your lens degrades the image. Better UV filters will degrade the image quality less. However good UV filters can be really expensive. The thin piece of glass may not be able to really protect the lens either in a catastrophic accident.
I had a UV filter causing strange problems on my Sigma 100-300 f/4 when I was taking photos of the Moon. As you can see from the following image, there is a ghost image caused by the UV filter. I believe this is due to reflections from the backside of the UV filter in certain circumstances.
Now I have taken UV filters off my lenses. I have decided to use it only when the environment I am going to shoot in makes it necessary.
Keywords: Filters, Lens Protection Filters, UV Filters