Archived posting to the Leica Users Group, 2007/01/18

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Subject: [Leica] binoculars - looking for assistance
From: marcsmall at comcast.net (Marc James Small)
Date: Thu Jan 18 20:21:30 2007
References: <82c9dd70701180437w53164f0as5cdf7876ee4dc0c1@mail.gmail.com> <9b678e0701181822k1af49093j513fc3c8d90d4667@mail.gmail.com>

At 09:22 PM 1/18/2007, Don Dory wrote:
 >Eric,
 >Traditionally birding binoculars need to be at the long end of what you can
 >hold to your eyes for minutes at a time with out eye fatigue due to hand
 >shake.  For most people that is in the 8X area.  People with steady hands
 >will go up to 8X and those with a coffee habit might have to go down to 6X.
 >Next, you want the brightest pair you can carry around your neck without
 >breaking it.  Birds tend to hang out in nice safe dark places so you need
 >the best light gathering you can get.  So, traditionally birders use
 >something like an 8X40 pair or even something like a 7X50.  Divide the
 >numbers and the closer you get to 7 the better for you; the human eye can
 >open up to about 7mm so if the cone of light coming out of the binoculars 
 >is
 >7mm or more then you are getting all that your eye can see.

Don

Your comment is a valid one, but the 7mm figure 
for the average size of the dark-adapted eye only 
works for teenagers.  By the time you hit twenty, 
your maximum size starts getting less and less 
and by the time you are 60, it's probably around 
4mm.  Anything beyond this is wasted light, so 
middle-aged folks can get as much benefit from, 
say, a pair of 6x,30mm glasses as from anything larger.

This topic comes up all the time on the Royal 
Astronomical Society of Canada list and we do 
have some dedicated binocular stargazers there!

Marc


msmall@aya.yale.edu
Cha robh b?s fir gun ghr?s fir!



Replies: Reply from don.dory at gmail.com (Don Dory) ([Leica] binoculars - looking for assistance)
In reply to: Message from faneuil at gmail.com (Eric Korenman) ([Leica] binoculars - looking for assistance)
Message from don.dory at gmail.com (Don Dory) ([Leica] binoculars - looking for assistance)