Re: Need help -- Wheelchair bound friend interested in astronomy

msimmonsmcse_at_yahoo.com
Date: 02/06/05 

Date: 6 Feb 2005 08:33:29 -0800

Thanks. I suggested a 7x50 cause its easy to hold in your hands as
opposed to the giant astro binos.

ezarenski@gilbaneco.com wrote:
> I would not recommend a 7x50 binocular as a first binocular. This is
a
> specialized binocular and it's performance will likely be compromised
> unless all these necessary conditions are met.
>
> First, it has a 7.1mm exit pupil, so unless you have eye pupils that
> large, your eyes will reduce the effective aperture of the binocular.
> If a 7x50 is used by someone with 5mm eye pupils, the performance is
> equal to that of a 7x35.
>
> If you have pupils large enough, because of the large exit pupil and
> the very bright image it produces, if this binocular is being used in
> skies that are anything brighter than very dark mag 6 or better, the
> views will be washed out by the bright backgroung glow. In skies
that
> get only as dark as mag4 to mag 5, the 7x50 will act more like a
7x35.
> A 10x50 in this case would be a better choice.
>
> A magnification of 7x for astronomy is very low. Sure it's better
than
> 1x eyes, but you see so much more as you increase magnification and
the
> consideration to use a mount leaves me thinking you want to be up in
> the range of 10x50 (still low), 12x50, 12x60, 15x70 or 20x80. I'd go
> for 15x70, because it has the best compromise of 4.3° for and
> magnification.
>
> edz

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