Oh, I can assure you an exit pupil is significant above 5mm, but it depends
on the general lighting conditions.
I have a pair of Vixen Ultima 8x56, with the exit pupil of 7mm, and a friend
uses the same brand, but 8x42 (exit pupil is 5.25mm).
In bright sunlight when your eye pupil stops down to something quite small,
less than 5.25mm there's absolutely no difference in the performance of the
two instruments (mine's just an awful lot heavier). The additional light
provided by my set simply spills out of my eye.
However at dusk when your eye opens up, the larger exit pupil is able to be
used, and the difference in the two binoculars becomes (very) apparent.
It's like turning the lights on.
Bill
-----Original Message-----
From:
On Behalf Of Vin Lam
Sent: Friday, 20 August 2004 8:45 AM
To: Paul Taylor
Cc: Mark;
Subject: Bird photography - the most versatile lens?
On Thu, Aug 19, 2004 at 09:58:07PM +1000, Paul Taylor wrote:
>
> Like binoculars, you also can't have too much aperture. A 400mm f/2.8
I would like to challenge this comment here. Unlike cameras, our
eyes are limited to the size of our irises in our eyes, which
also affects the aperture of the binoculars. Its like putting an
extra aperture iris inside the camera before the film plane.
I belive all binoculars have an exit pupil which eg. 10x50 gives
you a 5mm exit pupil. If your pupil(iris) is 5mm, then great, you
can make use of this. If they are only 4mm, then a 10x40 or a 10x50
will give the same brightness as you eyes are the limiting factor
and not the binoculars. This is why to some people, the 7x50s dont
give as bright an image as it should.
I have never measured up my iris or tried anything greater than
a 5mm exit pupil binoculars, so I cant really tell you if this
is true.
Regards
Vin.
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