Originally Posted by SpecialK
I've asked this question in a few of these threads but have never been answered...
If a "really good" filter costs, say $100-150, and is essentially a single multi-coated optically-flat piece of glass, why oh why are lenses so comparatively cheap? They may have 8 or more elements that are ground to some precision, plus focus/zoom/aperture mechanisms as well. Certainly a 16-50 or 50-135 is more than 5x complicated than a filter.
Because making the single flat glass really flat is difficult. Indeed it may be more difficult, than making a curved lens, because you get a regular curve by simply grinding and polishing long enough (random motion will produce a spherical surface). Grinding and polishing a real flat surface is more complicated. And in a filter you need two of these surfaces PLUS they even need to be completely parallel, which adds another degree of complication.
Then add to that, that filters have probably a much lower production run, than many lenses. A good filter will have dyed glass (even a simply Skylight filter has a slight colour) - and for any different filter you need a new supply of homogenously dyed glass.
If you then look at gradual filters, like Grey GRads, just imagine how complicated it is, to have the graduation completely homogenous along the whole peice of glass or resin.
And then, there is the marketing factor on top: Why would manufactureres sell a top-line filter for 50 USD, when we photogs are prepared to pay 100 USD? This is true for many other products too, so I don't blame the filter manufacturers.
Ben