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Old May 22, 2008, 1:08 PM   #1
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can someone tell me in very simple terms and words what a filter actually does for a photo?
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Old May 22, 2008, 7:48 PM   #2
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There's no such thing as "a filter". There are many types with different purposes.

I'm not going to provide a tutorial here as there books and web articles that cover the topic fully but here's a short list.

UV or Skylight filter - Blocks ultra violet light, may reduce slightly blue cast caused by excessive sensitivity to UV in some films and sensor. Generally a very slight effect at best therefore some use them to protect the lens surface. I don't buy into that because modern multi-coating on lenses is extremely scratch resistant anyway so the extra piece of glass is more likely to introduce other optical problems.

Polarizer - Reduces glare from reflections and can produce a more saturated blue in the sky.

Neutral Density (ND) - Reduces light reaching thecamera sensor so that a slower shutter speed or a wide aperture can be used for effect. Split ND filters are used to reduce light in part of the scene to allow the camera to more fully capture the dynamic range of the scene.

Special Effects - Many types here such as those that intentionally blur part of the picture, create star patterns from points of light and reflection, etc. Many of these can be duplicated by software.
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Old May 23, 2008, 4:52 AM   #3
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paintthesky wrote:
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can someone tell me in very simple terms and words what a filter actually does for a photo?
A filter filters.

That is, it blocks certain types of light while allowing other types of light to pass through to the lens and the camera. For instance, a red filter blocks everything but red light. Color filters are used mainly for B&W, but are ocassionally used for special effects with color as well.

But more pertinent to what you may be interested in, a UV (or Haze) filter blocks ultraviolet light which can make outdoor photographs hazy and indistinct, as well as create purple fringing (a kind of chromatic aberration.)

There are other types of filters, like neutral density filters and polarizing filters, whose purpose and effect is a little more complicated and are described well in ac.smith's post.
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Old May 23, 2008, 9:16 AM   #4
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Since the advent of digital photography, most filters have been rendered fairly useless, as their effects can be duplicated with more control in post processing. The ability to control white balance has eliminated the need to carry color correcting filters and/or different film emulsions. The only filters that are still useful (IMHO) are polarizers and ND filters as their effects cannot be easily duplicated. I'm not a big believer in protective filters, but many are, and this would be the only other reason to use a filter nowadays.
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Old May 23, 2008, 1:12 PM   #5
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rjseeney wrote:
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Since the advent of digital photography, most filters have been rendered fairly useless, as their effects can be duplicated with more control in post processing. The ability to control white balance has eliminated the need to carry color correcting filters and/or different film emulsions. The only filters that are still useful (IMHO) are polarizers and ND filters as their effects cannot be easily duplicated. I'm not a big believer in protective filters, but many are, and this would be the only other reason to use a filter nowadays.
I have had good luck with using UV filters to remove purple fringing when using pre-digital lenses on my KM5D.
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Old May 23, 2008, 2:45 PM   #6
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TCav wrote:
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rjseeney wrote:
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Since the advent of digital photography, most filters have been rendered fairly useless, as their effects can be duplicated with more control in post processing. The ability to control white balance has eliminated the need to carry color correcting filters and/or different film emulsions. The only filters that are still useful (IMHO) are polarizers and ND filters as their effects cannot be easily duplicated. I'm not a big believer in protective filters, but many are, and this would be the only other reason to use a filter nowadays.
I have had good luck with using UV filters to remove purple fringing when using pre-digital lenses on my KM5D.
I haven't heard of that being a benefit, but if it works then there is another reason. Purple fringing can also be fixed in post processing (I use Ptlens), and my D300 actually handles CA in camera automatically. I've had too many issue with flare, and image degradation to recommend using filters on an everday basis. I still use polarizers and ND's when necessary, but for the most part my lenses go naked.
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