Karen Nakamura wrote:
> >Does anyone know what the term "sharp cut" means with regard
> to a Canon
> >UV/Haze 77mm filter?
> >
>
> It means that the spectrum cut-off is sharp rather than a
> long drawn out
> affair. These are usually found in better and more expensive filters.
>
> You want to have a sharp cutoff between the visible spectrum
> which you let
> in and the invisible UV spectrum which causes haze. If the
> cutoff isn't
> sharp, then you're either cutting off some visible light (bad bad) or
> letting in some invisible haze (kinda bad).
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Karen,
You are right in what you say about cut off, but it is not necessarily the
better filters, just those that are using the better UV glass. UV Glass is
listed as L types. There is L37 (used in many Nikon and Minolta filters),
L39 the standard for Hoya and L41 which is only found in Hoya's Super HMC
Pro1 Line. The number represents wavelength, for example 39 is 390
nanometers or 3900 angstroms, and is the cutoff point.
Most modern lenses do not necessarily need L37 UV filters, but for those
times in high altitudes or near the ocean an L41 may help. For aerial
photography there is a B+W UV415 which is basically L41.5 glass and has a
slight yellow tint normal for glass above L41. This cast will appear in
photos taken at sea level. Incidentally, Canon filters are made by Tiffen.
Best way to check your UV filter is place it in a fluorescent light source.
The filter should show a yellow cast. The stronger the UV (higher the L#
glass) the more yellow you should see.
As for me I use L39 or L41 as needed and I do own some Tiffen Haze-2 filters
which if you look at have a very slight yellow cast to them. Good filter for
higher altitudes, otherwise use a Haze-1 or standard Hoya UV.
Peter K
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