Bird photography - the most versatile lens?

To: Paul Taylor <>
Subject: Bird photography - the most versatile lens?
From: Vin Lam <>
Date: Fri, 20 Aug 2004 08:45:00 +1000
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.


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