Camera Labs

Is there any time you should take a UV filter off? I have read that buying one for every lens and leaving them on is a good idea, as they serve as a good protection as well as filtering UV.

UV filtering isn't really needed, so they only provide some protection. They can induce flare or glare that wouldn't be there if they were fitted. If you see that happening, take them off. This is more likely to happen with a very bright light source in shot, such as the sun, or if you're taking a night shot with bright lights in it.

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.

It's basically insurance, protecting yuor lens against accidental damage, but personally speaking unless I know it's wet or there's going to be a potential risk, I don't use filters. Most are poorer quality than the actual lens and can degrade the quality. I prefer to use the lens hood, which keeps fingers and other probes from the front elements and also protects fairly well from knocks or minor blows.

I am a believer in hoods and lens caps. I only use UV filters when I feel there is a need for another layer of protection. One example would be weather-sealing, and another would be for ultra-wide-angle lenses, where the hood must be quite small. For such lenses, like my 10-22mm EF-S, I have purchased Heliopan multiple-coated UV filters, which are quite expensive, but do provide high optical quality, so as not to degrade the image.

Keep in mind that a fall could cause an impact that cracks the filter glass, and peens the filter's threads to the threads on the lens! The lens may well be usable, but getting the shattered filter removed may require a tip to a service center. This could effectively ruin an outing or trip, unless a spare lens is available. One of my instructors leads photo trips in the USA and internationally, and in one of her classes, she shows an image of just such a mishap that occurred during a trip in the California wine country.

This image, plus Gordon's recommendation for hoods, has made me a believer in lens hoods.

Keep in mind that camera shops tend to make a large margin of profit on cheap UV filters. They will really push a customer to purchase a UV filter with every lens.

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Canon 7D/5D/40D/1D2N; Nikon F6, FM3A, & Coolpix A; Canon 40mm Pancake, 135L, 50L, 35L, pre-II 50mm 1.8, 100mm 2.8L Macro, 10-22mm EF-S, 28-135 EF, 400mm 5.6L; Nikkor 50mm 1.2 AI-S, 50mm 1.4G, 50mm 1.8D, 16mm 2.8D Fisheye, 180mm 2.8D, 100-300mm 5.6 AI-S; Tokina 17mm & 100mm 2.8 Macro

For those who think every lens needs a filter, look up such lenses as the Nikkor 14-24 and Canon 14mm 2.8L. How does one readily get a filter onto them?

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Canon 7D/5D/40D/1D2N; Nikon F6, FM3A, & Coolpix A; Canon 40mm Pancake, 135L, 50L, 35L, pre-II 50mm 1.8, 100mm 2.8L Macro, 10-22mm EF-S, 28-135 EF, 400mm 5.6L; Nikkor 50mm 1.2 AI-S, 50mm 1.4G, 50mm 1.8D, 16mm 2.8D Fisheye, 180mm 2.8D, 100-300mm 5.6 AI-S; Tokina 17mm & 100mm 2.8 Macro

I agree with your points about filters, I learnt the hard way.

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Canon EOS 500D
Lenses: EFS 18-55mm IS, EF 50mm F/1.8 II

I like UV filters for everyday use but in high contrast situations or when I want the best image quality I can get, I take it off.

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Canon EOS 500D + Canon EOS 5D Mark III + Canon EOS 33v
Canon EF 24-105mm 4L IS USM + EF 100-400mm 4.5-5.6L IS USM + EF 100mm 2.8L Macro IS USM + Sigma 12-24mm 4.5-5.6 EX DG HSM + Canon Speedlite 580 EX II + Nissin Speedlite Di 466

Speaking as someone who has smashed 4 UV filters from impact (short falls, poorly manufactured camera bags), I will happily waste $80 for a filter that does nothing on the front of my lens. Yes, the filters did exactly what you described, and it was delicate surgery to get the filters off and the glass dusted off the lens. But would I trade that for buying a new $1600 lens? Um…

Of course you use hoods and caps when the camera's out. But when it's in a camera bag?

Taking it off when using the camera, well, sometimes I bother.

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D: iPhone 4S, Canon 5DmII, Panasonic DMC-LX3, Fujifilm F30, Canon 30D, Nikon CoolPix 8700 | A: Leica M3, Holga 120N, Contax Tvs, Polaroid Spectra, Canon 50E, Rolleicord, Canon AE-1P
Canon lenses: 16-35L II, 24-70L, 50 1.4, 70-200 2.8L IS, 10-22