[Guest]

[quote name='wim' timestamp='1340742629' post='19160']

Hi photonius,



Anybody trying to make you bleive this doesn't have the faintest idea of optics. A (decent) filter is a planparallel piece of glass, and has therefore in principle noimage forming refraction properties. It may have a potentially and extremely small image shift, certainly not focus shift. Focus shift is caused by spherical aberrations in a spherical lens (element), generally one with a very large aperture. A filter is not a lens at all. If that would be the case, it would change the FL too, like a close-up filter does, f.e. It just doesn't.

[/quote]



In principle yes, but as you say, there is a small offset. Could this offset affect bokeh with aspherical lens elements? I don't know.

Also, some Canon filters (to complete sealing) for (older) longer lenses are apparently curved rather than flat. Why, if not important?

Anyway, there are many factors influencing this, and based on my own experiences shotting both with and without good filters I'd say other factors influence sharpness and focusing more than good filters will ever do.



Kind regards, Wim

That's certainly true :-)

best regards