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Is it still required/highly recommended that I buy a UV or similar filter to 'protect' the front element of my lens?

I ask because this advice has been around for 30 years and you would think that the lens maker would have solved this problem with a built-in protection or something like that. It's good to check these old assumptions from time to time.

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-1 for being similar to…. IMO If every new user doesn't search forum before posting question, good answers will be repeated and spread out, making it harder for future readers to search. – Global nomad Dec 9 '11 at 10:42
This is a very common topic in general, and I'm surprised we haven't had a direct yet basic question on it yet. Everything I can find is either edging around the core issue (like the one Global Nomad points out) or more technical (like the one forsvarir noted). So while I definitely share the concern about duplication (and about new users searching first) my opinion is that this one is okay. – mattdm Dec 9 '11 at 11:35
P.S.: on protection filter pros and cons, also see… before writing a ranty answer. (Then go ahead with the rant if you still feel like it — nothin' wrong with a good rant; just want to place that context in the hope if avoiding flame wars.) – mattdm Dec 9 '11 at 11:39
up vote 29 down vote accepted

The front element of a lens is still (and probably always will be) a lens element, usually the largest and most expensive single piece of glass in the system. If you need physical protection for that element, you still have to add it (where the lens design permits).

Every element in a lens system contributes its own refraction and reflection. When you put an extra element at the front of a lens, light that would have reflected from the "old front" harmlessly into space will now reflect off of the rear (and front) surfaces of the new element. Those reflections can be minimized with coatings, but they are still there, and they still contribute to a degradation of the image. And keep in mind that the new element, whatever its shape, will still refract light and add its own distortions.

So you have a choice -- use the lens naked for best optical performance, or add a filter. When the filter is used for photographic reasons (neutral density, polarizers, color filters) you have a trade-off that's worth the price -- you give up the ultimate performance possibilities of the lens in order to capture a picture that the lens alone could not have captured.

You may be of the opinion that protection of the front element is also a reasonable trade-off at all times. I'd only use a "protective" filter if I was working in an environment that's likely to cause damage (say a windy day on the sand dunes or photographing someone using a grinder). For knocks and bumps, a lens hood offers good physical protection without putting anything in the optical path. But it's your choice—and it should remain your choice.

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what if the filter coating (…) is better than the lens coating? like a $400 filter on a $100 lens. – Michael Nielsen Jun 6 '13 at 15:07
@MichaelNielsen - makes sense on a Leica M8 (which is what the filter was actually designed for). And, perhaps, on a very wide-angle lens with a flat (or nearly flat) front element with insufficient coating. But one probably has to carefully consider the wisdom of using a $400 filter to fix but one of the problems of a $100 lens :) – user2719 Jun 6 '13 at 19:49

I looked through the manual for my Dad's old film SLR, purchased in 1982: nowhere did it mention protecting the lens with a filter. The Accessories section, which offered everything from bellows to cases (including those cool, now-retro cases that screw in to the tripod mount, flip over the top of the camera, covering both the camera and lens, and snap shut on the back) to microscope adapters, didn't list any filters except for two close-up filters.

The manual for his third-party telephoto zoom, from roughly the same time period, doesn't mention filters at all.

I looked at my more modern telephoto zoom lens' manual, and while it recommends using the hood to "protect the lens from rain, snow, and dust," the only mention it makes of filters is that they can be attached to the front of the lens, and suggests that you "use a polarizing Canon filter."

I interpret this to mean that for at least the last 29 years lens makers have considered the problem solved, and feel that their lenses are sturdy enough to not require additional protection.

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my father never had any either for his 1960s era Praktica, so add another 2 decades to that timeline :) – jwenting Dec 9 '11 at 9:48
To be fair, a default UV or a 1A "skylight" filter wasn't such a bad idea in the film days; either could significanly reduce image fogging and give you better contrast. Sensors now have their own UV filter. And early organic coatings would rub off if you stared at them too hard (the front coating of most of my "coated" -- not SMC -- screw-mount Pentax lenses had been cleaned off completely before I got them). So a walkin' around filter really wasn't such a bad idea at one time, even if it wasn't in the manual. – user2719 Dec 10 '11 at 7:03
Required is a little bit strong here. I use several of my Canon lenses that include this statement without filters. I'm willing to trade the very slight (in most shooting environments) additional risk for the improved optical performance. What use is owning a high performance lens if you are unwilling to use it to its fullest capabilities? In many cases by screwing a flat UV filter onto the front you just degraded the performance to the equivalent of a lens costing much less. – Michael Clark Dec 25 '14 at 18:21

My short opinion: I prefer to use a clear (or UV) filter for protection on all lenses at all times, removing it temporarily only if I observe artifacts.

The chance of something flying at my lens during normal use is not actually a big concern in the environments I shoot. More of a concern is that if I accidentally ram the front lens element into an object (e.g. when getting too close in or shooting through a window or wire mesh), or if I drop it a short distance, the lens has a better chance of surviving, which allows me to shoot more adventurously and get better shots. It may also be accidentally scratched during regular cleaning, if you forget to brush it - a filter allows the lens element to be cleaned much less often. If you stick with high-quality filters (e.g. B+W MRC) you get very high transmission and not much glare in most situations.

In the end what it comes down to is because my budget for replacement parts is very limited, I'm willing to give away a little image quality for a little insurance. However, they are not at all necessary - front lens elements are specifically designed to be exposed to the elements and cleaned regularly, and some include additional coatings for this purpose (e.g. fluorite coatings on Canon lenses). If you can get an affordable insurance policy on your equipment, that might be a perfectly acceptable alternative of similar cost.

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+1 for a considered answer. But, another alternative is to make sure you use lens hoods to protect the front element from those accidental bumps, and then "self insure" by saving all the money you would have spent on those high-quality MRC filters. Consider cost of repair times actual risk of damage — it may come out out lower than you think. – mattdm Jul 21 '12 at 14:05

still? It never was.
required? It never was, never will be.
recommended? Depends on who you ask. I'll say no, my dealer says no, many other people making money selling the things will say yes.
caveat: in some environmental extremes, it can be beneficial to protect the front element, but in those conditions you're likely going to need to protect the entire camera assembly, an underwater housing is likely a better option.

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You have a point, but lenses manufactures just provide the cap, there is no 0 element to protect the front element from scratches, fat and dust, all get in the way and if the front element is kept clean in an immaculate way you win.

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I keep a clear filter on all of my lenses, where possible. These are high-quality multi-coated filters, B+W for the most part. I do this not to physically protect the front element from impact, but to keep the front element clean and avoid cleaning the front element directly, which can wear down the coatings (it's almost always much cheaper to replace a filter than replace a lens).

Of course, a filter introduces an additional optical element and corresponding air-glass interfaces that degrade image quality. A good filter will keep this degradation to a level that is not perceptible under normal shooting conditions. I explain this in more detail here.

Filters aren't the best option for protection against physical impact, although there are several well-known cases where a filter took an impact and broke where the front element could have sustained damage instead. If protection against impact is what you need, consider getting a lens hood instead. A hood shields off light that shouldn't be part of the image, increasing contrast, and extends the lens beyond the front element so that the front element is much less likely to be damaged on impact. A filter is useful for keeping the front element clean, but you'll need to decide whether this is worth the image quality trade-off.

However, some Canon L lenses with weather sealing (several non-white L lenses that are not internal focusing or internal zooming) require a filter to be installed in order to complete the weather sealing. For example, page 1 of the manual for the Canon EF 17-40mm f/4L USM lens states:

Since the front element of this lens moves when focusing (zooming), you need to attach a Canon PROTECT filter sold separately for adequate dust- and water-resistant performance. Without a filter, the lens is not dust or water-resistant.

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