06-26-2012, 08:30 PM
Hi photonius,
[quote name='photonius' timestamp='1340627693' post='19093']
....
I suspect as much. Still, it would be nice to see really well controlled tests. Some say also it could be a focus shift caused by the filter. [/quote]
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.
Actually, quality of air, heat, and even position of th elight or lighting relative to the lens have much more influence on focusing, sharpness, colour, etc., than any decent quality multi-coated UV filter will ever have. Therefore the only reliable test setup for such a test is one indoors, and so far I have never come across any. Furthermore, a lot depends on how the lens is held, whether IS is turned on or off, and how IS is used (it requires a second or two to stabilize on the 100-400), and shutter speed. Shutter speeds of 1/30s to 1/250s on the older 5D f.e. tended to give trouble by providing more mirror slap at these shutter speeds.
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
[quote name='photonius' timestamp='1340627693' post='19093']
....
I suspect as much. Still, it would be nice to see really well controlled tests. Some say also it could be a focus shift caused by the filter. [/quote]
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:Anyway, here is a somewhat reasonable test on a 100-400, where a Giotto's UV filter doesn't work so well, while two others are fine:
[url="http://forums.dpreview.com/forums/readflat.asp?forum=1029&thread=33481535&page=2"]http://forums.dprevi...33481535&page=2[/url]
Actually, quality of air, heat, and even position of th elight or lighting relative to the lens have much more influence on focusing, sharpness, colour, etc., than any decent quality multi-coated UV filter will ever have. Therefore the only reliable test setup for such a test is one indoors, and so far I have never come across any. Furthermore, a lot depends on how the lens is held, whether IS is turned on or off, and how IS is used (it requires a second or two to stabilize on the 100-400), and shutter speed. Shutter speeds of 1/30s to 1/250s on the older 5D f.e. tended to give trouble by providing more mirror slap at these shutter speeds.
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
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....