On any photography forum out there you are likely to see heated discussions about the value (or lack of) of using UV filters on today's digital cameras. I think it has been pretty well established that there really isn't any need these days to "filter" UV. UV filters were more applicable to film cameras due to the sensitivity of film to UV light. Digital sensors not so much. Most people who use UV filters on digital cameras do so for "protection" which is understandable given the cost of a really good lens these days.

Well, Sigma has come out with a transparent ceramic "protector" (not really a filter since it does not filter anything) that claims to be much stronger than the chemically treated glass in today's UV and other filters. If you are just looking to protect an expensive piece of glass, this looks pretty interesting as an alternative to a UV filter.

http://www.dpreview.com/articles/0022492...r-glass-ceramic

I've got some glass that is quite expensive and I might consider these. Thoughts?

I think the hot mirror that come in most cameras filters out UV as well as IR. When I switched the hot mirror on my camera for IR, there were several options to choose from including full spectrum, which is just a clear piece of glass.

I didn't see in the article if the entire "filter" is made from ceramic, or if it is a coating on the glass. I wonder how transparent aluminum would work.

My understanding is these are solid clear ceramic, not just a coating. (The ring is metal) They are also supposed to be very nearly optically pure such that there would be no perceptible degradation of the image. Sigma claims them to be 10x the strength of chemically treated glass in which only the surface is hardened. These protectors are not cheap, but if I had a $2000 lens like the New Canon 100-400 Mark II it might be worth it.

Most of my lenses have 52mm screw mounts. I'm not seeing that size for the ceramics, at least not yet.

Heavy on the 52mm ring size=Nikon.

For my taste, a ring of "extra" material on the front of any lens is protection for both the optic and the threads. Had my share of "dents-n-dings" and found it cheap insurance.

I know on most photo forums I've been on, the question of whether to use a UV filter for protection or not is always a topic of continual debate. I used to always use a UV filter, but these days I've decided to not use them and instead rely on a good lens hood for protection. The exception would be if I was going to shoot an event where flying debris was possible, like an auto race or dirt bike race, etc.

As a photojournalist, just about everything I'd cover had the probability of "flying debris" at some point!