Quote:
Originally Posted by Ledgem
My only filter experience is with a Hoya UV single-coated filter (cheapest) - I don't know whether multicoated or any of the fancier ones that cost 6x as much are much better. I've read that the UV filters can cause some reflections when taking pictures in low lighting, but have yet to test it for myself.
But I'm being unfair - your guide is for buying lenses, and it's a superb guide for that. I guess I'm craving some of the more technical details that I still don't understand or have just mastered (aperture, lens care, etc.)
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Yup. I didn't say a word about filters. In digital photography basically only filters you might really need are special effect filters and polarizing filter. Most of the camera sensors have quite good uv-filters built in so in effect they're primarily used for protective purposes. Colored filters are pretty much history because it's far easier to get the same effect with photoshop.
Filter coating is actually an old subject for debate. General consensus is that filters always have a negative effect on picture quality but what's fought over is it's significance. Filters are coated for the exact same reason as lenses. In best camera lenses each individual lens is multicoated. Uncoated filter can actually block up to 10% of the light. Block may be a bit poor choice of words though. Coatings in lenses and filters are anti-reflective. So when using a uncoated filter part of the light is reflected on each of the filters glass-air interfaces. This is a bit of a problem because part of the light passing through the filter can actually be bouncing back and forth within the filters interfaces. This reduces contrast especially around highlights and in parts of the picture that has strong contrast. The mechanics are in effect the same than with lens flare but the results because of the small size of the optical element are far less distinct.
Coating works by creating a canceling wave within the lens or filter. An extra interface is created within the filter that's about half the wavelength in thickness to the wavelength you want to cancel thus there are basically two reflected rays of light which are in opposite phase and thus cancel each other out. There in lies the problem with single coating. It works in a very limited wavelength range. Multicoated lenses have several of these filtering layers and so they're effective for a wider wavelength range.
Wikipedia has actually rather good run through of basic filters. It's a bit superficial though but list quite well what's available.
If you have any questions don't hesitate to ask. I'll do my best to answer.
I'll be talking about colored filters a bit in the B/W photography guide. I'd just need the example photos which is proving a bit difficult. Maybe in 3-4 weeks I'll find the time. Vacation coming up.