Re: Full/near-full moon and Telrad


Jay Swartzfeger wrote:
> 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

Even so, some would agree whole-heartedly with the content of your
original post. <grin>

.

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