On Mon, 22 Feb 1999 14:40:50 -0800, Zareh Movsessian wrote:

>I have a couple of questions pertaining to the use of filters. I would
>like to know what each of the following are used for:
>
>- UV/Sky: Is there a difference? Are there any other types? Any use
>besides front element protection?

No, except that the skylight can subtly warm slide images...

>- Red 25(A): What are it's applications for Black and White? If any,
>for color?

Useful for B&W infrared, and for darkening blue skies
in B&W - little color-film usefulness...

>- Yellow: What are it's applications for Black and White? If any, for
>color?

Unless the sky is VERY dark blue (high mountain areas, clear sky),
the light and medium yellow filters are a waste of
film speed - though the dark yellow can slightly darken
a normal clear blue sky. Yellow is sometimes useful for IR
color films. BTW, the "examples" often seen in filter brochures
tend to be somewhat exaggerated in effect...