Does my L lens need UV filtering, or does it already cut out UV?

Question

Now I know the "should my expensive lens have cheap glass on the front?" is an age old question that will never be agreed upon and ends up down to preference. What I'm interested in is the UV vs non-UV perspective.

I'm looking to get a Canon 70-200 L f/4 IS in the next few weeks and obviously as soon as it comes out of the box I want to protect my baby. I may over time decide that a filter on the front to protect it isn't needed but I'll definitely want one to start with. What I want to know, and can't seem to find online (as it returns arguments about filter-or-not) is: does the L lens need UV protection?

The L lenses have a lot of complicated glass in them with various coatings to that glass, and is that arrangement, or any specific coatings, already designed to cut out any problems caused by UV?

I am deciding on whether to get a Hoya Pro protector filter or UV filter, but if the L lens is already designed to remove problems caused by UV I would prefer to have the clear filter to remove any potential problems caused by another UV limiting element. I know the benefits a UV filter can give to a normal camera/lens setup so no need to be letting me know the pros and cons of that.

Answer 1

If you are interested in protecting the lens itself, namely the front lens element, then a lens hood will generally perform that job quite well. I do believe that lens comes with a hood in the box (make sure that your buying from a reputable dealer, as shadier ones often remove those items and up-sell them as extras!) I have the Canon 100-400 L IS, and I have never used it without the hood. It is far too easy to bump the front of the lens into things that you just don't realize are there, and a hood offers far more protection for such encounters than a simple UV/P filter. A lens hood might get scraped up, but it only takes a moderate amount of force to completely crush a UV/P filter, and the slimmer ones that don't cause vignetting sit close enough to the front lens element that a solid crunch might still scratch the lens glass.

As for filtering out UV light, I don't think that is really a concern these days with digital camera. Glass itself is a UV filter, as most glass, even the cheap glass in a normal window, block 90% of UV light. Lower-frequency, or near-UV light in the 400-380nm wavelengths range, may not be fully filtered by the glass of the lens itself. Despite the supposed "common sense fact" that camera sensors have UV filters in front of them, that is actually a misnomer. Most digital cameras have a filter stack in front of them that includes an IR filter, a set of horizontal and vertical low-pass filters, and possibly some multi-coating...but they usually do not include a specific UV filter.

(From DPReview of Canon 5D Mark II)

If you really want to filter out those near-UV, you might throw on a quality UV filter (make sure you find some reviews that actually test them, as many UV filters are no better than the glass already on your lens, and they often reduce the quality without providing any real UV filtering.) I would say do without it, as it really won't provide any better physical protection than the lens hood, and could impact the quality of your photos.

Answer 2

As far as I know the lens doesn't offer any specific UV filtering apart from the fact that all glass filters out high frequency UV. Your digital camera sensor does have a specific near visible UV filter on it so UV shouldn't be a problem. The only reason I can think of to use a UV filter on the front of a lens is if you're going somewhere UV is a major problem such as the far north (anecdotally this includes the tip of Scotland, Scandinavia, Arctic Circle) or if you have a camera with insufficiently strong sensor UV filter such as the Leica M8!

Answer 3

According to @jrista's comment on this answer, some canon lenses are more weather-sealed when they have a filter on.