Re: [APML] Binoculars. was: Petzval hot spot?

["Bert Katzung" <katzung1@attbi.com>]

Hi Roland:
Have you compared the Canon Image Stabilized binocs? I don't know how they
compare in terms of even illumination, but if you haven't tried a pair late
at night when you're fatigued and ordinary binoc images are jumping around
like an earthquake, you owe it to yourself to borrow a pair. I am addicted
to mine.
Bert

Bert Katzung
katzung1@attbi.com
www.astronomy-images.com

----- Original Message -----
From: <Chris1011@aol.com>
To: <astro-photo@seds.org>
Sent: Wednesday, September 18, 2002 10:05 AM
Subject: Re: [APML] Petzval hot spot?


> Speaking of hot spots in scopes, I have seen a marked deterioration of
> quality in binoculars of late.
>
> Last weekend I was at Astrofest. Lots of vendors selling stuff. Since I
was
> in the market for a good pair of binocs, I checked out just about
everything
> that was available. Every one of them had the same problem - uneven
> illumination of the exit pupil. Yes, most of them had Bak4 prisms. That in
> itself does not produce even illumination. Some binocs had 60 and even
70mm
> apertures, but with internal field stops that limited even the on-axis
> apertures to between 40 to 50mm. Edge illumination on most of them was
equal
> to about 30mm aperture. The reason for this is that the prisms are too
small
> in virtually all binocs - even models costing $400 and up. The effect is
the
> same as undersize diagonals on a Newtonian. Why do they put big lenses in
> front and small prisms inside? Because the general public is not aware of
> simple optical principles and it saves money, size and weight.
>
> I guess I will have to spring for costly Zeiss or similar binocs to get
full
> illumination of the field (or maybe put up with some light falloff).
>
> Roland Christen
>
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