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Do cheap lens filters (UV, ND, CPL) affect image quality, color reproduction, sharpness, etc.? Do they really offer protection?

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Does cheap lens filters (UV, ND, CPL) affect on image quality, color reproduction, sharpness and etc.?

All filters affect image quality in some way or other. Some effects are desirable, and these are usually the reason for using a filter in the first place, and some are undesirable. Inexpensive filters are usually built to a lower quality standard than more expensive ones, and so they often have more undesirable effects. Low-quality filters are more likely to cause problems like lens flare, distortion, unwanted color cast, and vignetting. Better filters are more expensive because the features that help avoid these problems add to the cost of production. For example, multi-coating both sides of a filter adds a number of steps and requires extra equipment and materials.

And do cheap UV filters really do protection job?

Yes. Physically protecting the front element of a lens is the other reason that people typically add a filter to their lens. It certainly does work: with a piece of glass in front of the lens, the front element is protected from dirt, dust, moisture, fingerprints, etc.

There's a bit of a tradeoff here, though: you don't want to spend a lot of money on something that's intended to sacrifice itself to save the lens, but you also don't want to put something in front of the lens that's going to adversely affect the photos you're taking. There's not one right answer; in choosing whether to use a protective filter, you need to consider such things as the cost of your lens, the cost to repair any damage to your lens, your budget, the environment in which you use your camera, and the down side to whichever filter you're considering.

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    I like to call it "ablative armour" :) – Lightness Races with Monica Feb 23 '17 at 23:32
  • "problems like lens flare" should be "problems like unwanted lens flare". Sometimes lens flare is desired, especially if your name is JJ Abrams. – Pharap Feb 24 '17 at 14:41
  • @Pharap I don't dispute that sometimes lens flare is intentional, the meaning here is pretty clear. You could make the same argument about any optical issue. There's probably somebody out there making creative use of chromatic aberration, too, but we don't bother to say "unwanted chromatic aberration." – Caleb Feb 24 '17 at 15:03
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I realize that I missed the "Cheap" part of the question, SORRY! I hope my answer still might be useful to someone though.

Yes. (For protection).

You wont scratch your lens that easily with a UV-filter on, however, a lens hood does this job real nice too. I always keep my UV-filter on my 17-40mm f/4L lens, cause this is my go to lens when I shoot photos close to the ocean or other places where salt or dirt might be flying around.

Also, if your camera body and your lens is weather proofed, a UV-filter, or a filter of any kind is the last step of completely weather sealing your gear!

I don't notice the filter on my photos, but I use a "more expensive one", the B+W 77mm for about 110$. I believe that the way to think here is, don't put a cheap filter on a expensive lens. I wouldn't for example, put a UV-filter on my 50mm f/1.8, cause I might just as well buy another lens if it gets damaged.

So, from my point of view, I rather have a nice UV-filter on my lens and be able to go shoot in rougher environments than have to be more careful and miss a great opportunity .

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Do cheap lens filters (UV, ND, CPL) affect image quality, color reproduction, sharpness, etc.?

All lens filters affect image quality, color reproduction, acutance, etc. to one degree or another. Cheap ones usually affect these to a greater degree than better filters do. Sometimes to a much greater degree. Sometimes a cheap filter can actually damage your expensive lens just from spinning it on. The flat surfaces of filters can also cause noticeable reflections in captured images. This is exacerbated with the higher reflectance of the filter stack in front of digital sensors as compared to film. For a shooting situation in which a flat filter will almost certainly cause problems, please see What kind of filter (if any) should I use when photographing a theater scene?

Do they really offer protection?

Both yes and no.

They offer protection from some specific environmental concerns. If you are shooting in the following kinds of conditions a filter can help protect your lens from damage:

  • Wind blown sand or dust. Exposing the glass of your lens to a strong sand storm can ruin it in a matter of minutes.
  • Water vapor or spray, particularly salt water spray which is very corrosive to the materials inside your lens and camera.
  • Manufacturing environments that involve grinding, certain types of welding, molten metal or any other process that results in very hot, very small projectiles that could hit the front surface of your lens.

Some lenses are rated "weather resistant" or "weather sealed." Some of these lenses specifically require a protective filter to complete sealing (e.g. EF 17-40mm f/4). Other lenses don't need the filter because the front is already sealed. These are usually lenses with internal focus in which the front lens element does not move in relation to the front lens barrel (e.g. EF 70-200mm f/2.8 L IS II).

In the most extreme conditions, such as the very fine particles encountered from "color bombs" at a color run event or other type of celebration that uses them, even filters won't offer much protection and more extreme measures will need to be taken. See, for example, How to protect camera and lenses against "color bombs"?

Using your camera unprotected in an alkali dust environment like the area used for "Burning Man" can ruin the entire camera, not just a lens. The dust that makes it inside the camera will destroy moving parts as found in mirror and shutter assemblies. Even well-sealed cameras need extensive cleaning.

What filters don't really do is protect a lens when it is dropped or impacts another object. A well made lens hood is much better protection in this regard and doesn't impose any optical degradation.

  • Just because a flat thin filter shatters from an impact does not mean that the front element of the lens would have shattered in the absence of the filter. Lens elements are much thicker, made of harder, denser materials, and often shaped in a way that helps transfer the energy absorbed in an impact to the lens barrel. Filters are thin and brittle and scratch or shatter more easily than the optical glass used for most front lens elements.

Don't believe me? Check out this video in which various impacts to a lens result in no visible scratches. It takes a really hard strike with the sharp claw end of a hammer directly to the lens glass to leave any visible marks!

  • When a filter shatters it can increase the likelihood and number of scratches to the lens' front element. All of those shards and bits of filter become miniature blades and grains of sand, possibly being grinded against the lens' front element and scratching it. For more, please see How to clean shattered UV filter glass from Lens?

  • The most likely damage to a lens from a hard impact is to the internal alignment of optical elements. A filter does nothing to lessen the shock of an impact that strikes the filter ring or any part of the lens itself. In some cases an impact can deform the filter ring's soft metal and make removing the filter without further damaging the filter threads on the front of the lens difficult or impossible.

Deciding whether or not to use a filter as a protective measure should take many factors into account:

  • The cost/benefit ratio of using a filter. Is the cost of a quality filter more than the cost of an inexpensive lens or the cost of a front element replacement? In which case it would be cheaper to repair or replace the lens than to replace the filter! The cost/benefit factor must be carefully weighed individually for each lens in question.
  • Environmental conditions (see above).
  • The minimal or even non-detectable effect of minor front element scratches on optical performance. Ditto for normal amounts of dust in a lens.
  • The cost of using a filter in terms of optical image quality.
  • The availability of other protection that can increase optical image quality rather than decrease it and provides more protection from certain types of impact. They're called lens hoods.
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    This is the best answer and should be voted up. – Mike Sowsun Feb 24 '17 at 12:25
  • Thanks for the vote of confidence, Mike! It's too balanced in the middle of the road to get many votes, though. Those who think UV filters are necessary protection against a lens apocalypse every time they go out to shoot read it as being anti-filter. Those who think UV filters are the lens apocalypse read it as pro-filter. And who wants to read informative links on all sides of the issue when it might force them to... gasp!... modify their opinion? – Michael C Feb 24 '17 at 20:56
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UV filters can be useful to protect the lens against condensation. You can take pictures with the UV filter removed, you don't want reflection artifacts to appear. When you're done you can blow off dust off the lens using your rocket blower, screw the filter back on, put the lens cap on and put your camera in the camera bag and put everything in a large airtight bag that you can close. This way you'll have trapped several layers of cold, bone dry air. The back at home you should wait several hours until the camera has seated up to room temperature before you unpack the camera.

If you had walked back into your house with the camera hanging from your neck with only the lens cap, lots of condensation would have appeared on the lens. Some of this may enter the camera body, but even if it all stays on the lens it will cause problems due to letting dust particles stick on the lens when that condensation dries up (some dust particles will contain salts that will dissolve in water, when that water is evaporated the dust particles will stick to the lens). Also over time you'll get fat deposits on your lens.

This means that a rocket blower will not be able to remove as many dust particles compared to having the UV filter mounted for most of the time. That would makes it necessary to wipe off the dust using a microfiber cloth much more often, and every time you do that there is a risk of scratching the lens (some dust particles may be abrasive).

  • Oh no! I've got lenses I've been using without a filter for over ten years. How do I check for fat deposits on my lenses? – Michael C Feb 24 '17 at 20:40
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In a perfect world our cameras would yield a faithful image of the outside world. In reality every lens has uncorrected aberrations that distort. There are seven aberrations, of which five are monochromatic:

  1. Spherical
  2. Coma
  3. Astigmatism
  4. Curvature of field
  5. Distortion two color aberrations
  6. Longitudinal
  7. Transverse.

Again, all lenses suffer from residual, uncorrected aberrations.

To mitigate the seven aberrations, lens makers play with the shape (figure) and the material of construction. The end result is a compound array of lenses, each with a different power, and some with dense glass and some with less-dense glass.

Each element of the lens array has two polished surfaces. Some elements are air spaced, some are cemented together. No matter how spaced, each surface reflects away some of the imaging forming light rays. These unwanted reflections reduce the brilliance of the projected image. The loss per surface translates to each element passing approximately 92% of the light. The accumulated loss is nearly 50%. Worse, much of this stray light will be re-reflected by lens-to-lens junctions. The end result is that the film or sensor is bathed by this stray light, and the result is flare. Flare is devastating; it robs our images of contrast.

To mitigate the light loss via surface to surface junctions, the lenses are given a thin mineral coat. The coat must be ¼ wavelengths thick. Further, a coat is optimized for just one color. A modern lens has multiple coats. A coated lens passes better than 98% of light.

You add a filter: You are adding two additional polished surfaces that induce additional reflections and add flare. Now the typical lens has a curved figure. The filter is flat and the two surfaces are parallel. It is a fact that an optical flat is very difficult to make. The bottom line is, you should never add a filter unless the benefit outweighs the harm.

Mounting a UV filter is beneficial when doing aerial photography and imaging distant landscapes. A UV filter is valueless when doing general photography. Additionally the modern digital camera sensor is highly sensitive to UV light. To mitigate, the camera maker adds UV filtering to the protective cover glass of the sensor. Thus an additional UV filter is redundant. The UV filter mainly protects our precious lenses from scratches. It also serves to line the pockets of camera accessory businesses.

  • How does a UV filter provide any benefit for aerial photography or distant landscapes that isn't already provided by the UV filter in the sensor stack of the vast majority of digital cameras? – Michael C Feb 24 '17 at 4:22
  • @ Mr. Clark -- As you know, ordinary glass is a UV blocker and lenses are glass, plus lens coating all limit UV transmission. Additionally the cover glass over the sensor limits UV. Anyway, the typical digital sensor has lowered sensitivity to UV as compared to photographic film. I have not seen any studies that tell me that a UV filter is beneficial when mounted on a digital camera. What is your take? – Alan Marcus Feb 24 '17 at 5:47
  • The lead sentence of your final paragraph strongly implies you are maintaining such a position. – Michael C Feb 24 '17 at 15:59
  • UV is subdivided into A long wave, B medium wave & C short wave. At high altitudes, B and C are prevalent. Water / ice particles vary in size, > 1000 Mu, photons hits are absorbed. Smaller and hits cause vibration and light is re-emitted. Different size particles induce profound differences in the color of re-admittance. Different filters are available and advisable for aerial work. A Sky Light is a warming filter that reduces bluishness as it absorbs UV. Circumstance dictates different mitigating filters. I say mounting a UV when doing aerial is good advice. – Alan Marcus Feb 24 '17 at 17:02
  • The slight color shift obtained with a skylight can be replicated merely by changing the R and B multipliers when demosaicing digital files. That's how color temperature and white balance are set. – Michael C Feb 24 '17 at 20:38

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