Why "protective" filters are a bad idea:

Started Jan 7, 2011 | Discussions thread
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Steve H
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Why "protective" filters are a bad idea:
Jan 7, 2011

I posted this in response to a question in the Canon Lens Forum. At the risk of stirring up a hornets' nest, I thought it might be useful to beginners asking the same question here. So why is using a "protective" filter 24/7 a bad idea?

They degrade IQ . Sometimes they throw off AF which results in minor misfocusing and softness. Sometimes they make a mess of a len's bokeh. Sometimes they add flare spots and ghost reflections. Sometimes they reduce contrast. Sometimes they don't - often it depends on the particular shot, angle of light, lens in question. It's like Russian roulette - there may be no discernible difference in some shots, others will be ruined. Best of luck.

"Protection" is usually not necessary, and when it is you'll know beforehand. Far from being an anti-filter Philistine, I do have a UV filter to fit each of my lenses in case I use them in really harsh conditions - conditions where I would also be using eye protection. My eyes are actually quite a bit more valuable than a lens front element so it seems to me twisted logic that I would have a UV filter fitted to my lens 24/7 for "protection" and yet not do the same for my eyes. So who wears safety glasses all day in case a foreign object appears out of left field and embeds itself in a cornea?

Often they don't protect - they make matters worse. Fitting a filter, then adding a lens cap is asking for trouble. Plastic lens caps have deep centre sections which almost touch a filter glass but which easily clear a front element. If the camera/lens gets dropped front first onto the ground (usually what happens) with a lens cap on its own, the cap will probably protect the front element from damage. Add a filter to the mix and the centre of the cap will smash the glass and force broken shards into the front element and often the lens itself. In many cases the only damage to the lens is caused by the filter.

Lens hoods do a better job of protecting a lens and significantly improve, rather than degrade, IQ. Drop a lens with a hood fitted and it will almost invariably survive - the hood will deform and eventually break but in doing so it protects the lens from impact. Just like the crumple zone on a motor car. Filters don't deform at all, they transmit the full force of the impact to the rest of the lens and usually shatter in the process creating shards of broken glass, which, unlike a soft plastic cap or hood, are sharp and hard enough to cause front element damage.

They don't make economic sense. Ignoring that there are more effective method of protecting a lens, it's cheaper to buy insurance to cover damage than it is to invest in a high quality filter for each lens. And of course insurance will cover all damage, ironically including damage caused by a filter!

My advice? If you are going to use a lens in really harsh conditions (fast blowing sand, weld spatter etc.) in which you will also need to protect your eyes, buy a moderately priced, multicoated filter and use it only when necessary. Always use a lens hood and a use a cap when you don't need to be shooting. And for the record, I've been a photographer for 30 years, have around $15,000 in gear and I have never scratched or damaged a front element.
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Steve H

Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too? - Douglas Adams

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