Re: Full/near-full moon and Telrad

In article <a3dc6$437ec9e0$471d5265$7219@xxxxxxxxxx>,
David Knisely <KA0CZC@xxxxxxxxx> wrote:

> Tony Flanders posted:
>
> > Full Moon under an otherwise pristine sky is a tad darker than a
> > moonless night
> > at my home in Cambridge, MA, so I'm pretty familiar with observing
> > under these
> > conditions. You might be surprised how many stars you can see if you
> > try --
> > somewhere between mag 4.0 and mag 5.0 except right near the Moon, I
> > would
> > guess. Of course, you won't be able to see all of those through the
> > Telrad
> > window, which darkens the view considerably.
>
> I doubt there is much true darkening, unless you are referring to a time
> when the reticle brightness is set rather high reducing the
> effectiveness of night vision. The Telrad window itself is bare
> (uncoated) glass of reasonably-good quality. It might lose around 10
> percent of the light that goes through it, but this would be only around
> 0.1 magnitude of a difference. Visually, I see more of a limitation
> caused by external light sources bouncing off the glass or other local
> nuisances than any "darkening" that the glass itself might induce.
> Under a dark sky, I don't see a huge amount of dimming of the sky as
> seen through the window (unless there is dew), as most of the time, I
> can still see useful target stars well past magnitude 5.5 through the
> glass. A simple dew shield that blocks stray light from areas where it
> might enter the window can be an effective strategy to getting the
> Telrad to work better under local illuminated conditions. Clear skies
> to you.

David, see my other post. It was user error.


--
Jay Swartzfeger
http://www.swartzfeger.com
Scottsdale, AZ
.

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