----- Original Message -----
Sent: Friday, October 24, 2003 9:41 PM
Subject: Re: [M]: Skylight filter


> Rick,
> This filter is named wrong. I have been using one since day one
> of my Lx200. It is really should be named a dust filter. This filter
> does nothing more than keep dust from entering the OTA. It does not
> effect your VIEWING in any way. Been taking astro pictures for years
> with not ill effects from the filter.
>
> Barre
>
> I bought a Meade 1A skylight filter for the back of my scope. But it
> seems to me that 1) it isn't coated, thereby losing a lot of light, and
> 2) it is constricting the light path. Am I off base here, or is this
> filter seriously degrading my telescope? Can anyone shed a little light
> (no pun intended)?
> The Meade Skylight
'Skylight' filters, are a standard photographic accessory. They normally
block near UV slightly. When taking daytime photographs, film is more
sensitive to UV, than the human eye, and long distant views, that are clear
to the eye, can be washed out on the photograph, by this light.
Their use in the night time, is far more dubious, since the Sun is not
present in the sky (which is the 'source' of the light in the daytime).
Effects will be most visible towards the horizon, where there _may_ be a
tiny reduction in the distributed light (not light pollution though, since
most of this is at too short wavelengths), on slightly 'misty' nights.
However the effect is so small as to be allmost imperceptible.
Skylight filters, are commonly fitted by photographers to lenses as a way to
protect the main optics, so the comment to treat it as purely a 'dust
filter', is spot on.
Whether the restriction in the light path is significant, will depend on the
focal ratio you are running, and the field of view in use. Most such filters
are coated, but often with a relatively simple coating, rather than some of
the more complex coatings. The light loss, will be very small.

Best Wishes

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