UV Filters: Should you be putting another bit of glass in front of your lens?
Are you a filter person? I confess an addiction to UV filters as protection for my lenses. I hate lens caps and usually leave them in the original box together with other accessories. If not, I lose them and have to scrabble around when it comes time to sell. I tend to buy good-quality filters, often B&W if a convenient Leica filter doesn’t fall into my lap, and I have clear evidence of their worth in protecting the front element — in a way just as good as a lens cap and far less hassle. Provided you keep them clean, there's nothing to object to. Or is there?
I have friends who are opposed to UV filters getting between their lens and their subject. Some don't even bother with the lens cap and are happy to let their front elements take care of themselves. Others are forever clipping and unclipping the lens cap, a procedure that makes me wince.
Logically, putting another piece of glass — however refined — in front of your lens must impede image quality in some small way. And the poorer the quality the filter, generally the more reflection there is. As with everything, though, there are different schools of thought.
Back in December last year I read an enlightening article by Lens Rentals' boss Roger Cicala on the pros and cons of using filters. Lens Rentals see the best and worst of everything, I imagine. And, like the eye hospital, they probably like to err on the safe side when it comes to protecting the front elements of their stock. Yet Roger takes care of around 20,000 lenses at any one time and has found that 75% of them never suffer a problem. So, he reasons, it's a matter of working out the probability of harm to image quality against the potential costs and disadvantages of a filter.
He makes the point that replacement of lens front elements has become much more expensive in recent years, but in the main he is dealing with less expensive brands. I have no idea what it costs to replace the front element of a typical Leica M lens, but I'm afraid to ask. It will probably make even the priciest Leica filter look like a bargain.
Roger's advice, as it turns out, is equivocal:
"So does this mean you should put a UV filter on all of your lenses? No. I still recommend looking at the cost-to-benefit ratio for the specific lens, and considering what you’re going do with it. If it’s a lens for studio portraiture only, why bother? If you shooting surf at the beach, then you better wear protection.
"In most cases, a lens hood (actually mounted on the lens, not left in your bag) provides plenty of front element protection. Wide-angle lenses are a unique case, though, since those hoods don’t provide much protection. But if you are outdoors and your lens is exposed to dust, sand, water, or other things lenses don’t like, then a hood doesn’t provide protection and UV filter is probably worthwhile."
Roger has had a lot of interesting things to say on the subject of lens filters. In one article he argues that filters can seriously harm image quality, but last week Roger published what he hopes will be his definitive roundup — including an interesting table comparing the performance of UV filters from different manufacturers and at various price levels. He based the comparison on a 77mm filter size and listed the reflection percentage — the lower the better. What I found surprising was that the Leica UVA II filter had the lowest reflection of the lot, a mere 0.1%. The downside of this particular filter is that it costs $225, according to Roger. Again, while it is a high-performance filter, it's a toss up between cost and slight image degradation against the potential front element replacement. As he concludes, after publishing a number of very interesting comparison lists,
"You can determine what you want to call acceptable and not acceptable. To me, there’s a very obvious break between filters that reflect about 0.5% or less and those that reflect 1.3% or more. There’s another big gap between the three filters at the bottom of the list and everything else. Whether the difference between, say 0.3% and 0.5% is significant I don’t know, and if there is a difference it probably only shows in certain conditions. I’m pretty confident the difference between 0.5% and 1.3% is significant, though, and I’ll bet my house that 8% reflection causes problems."
If you can’t make up your mind whether or not to fit a protective filter to your lenses, you can do a lot worse than take Roger’s advice.
Here is another interesting reference which I came across thanks to reader Frank Neunemann: Leica: If we had intended our lenses to have flat pieces of glass in front, we would have designed them that way."