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binoc recommendations
- To: carolinabirds@duke.edu
- Subject: binoc recommendations
- From: Tom Krakauer <tkrakauer@mindspring.com>
- Date: Tue, 13 Jun 2000 14:19:53 -0400
- Sender: carolinabirds-owner@acpub.duke.edu
The eye relief is, as was pointed out, is important. As is the alignment
issue.
The other important consideration is the size of the exit pupil. Divide
the objective size by the magnification to obtain the exit pupil e.g. 42
mm/ 8 power = 7mm The exit pupil is the size of the spot of light that
enters you eye. Your pupil can dilate to about 7 mm. The 10 X 21 Nikons
that were recommended give a maximum exit pupil of 2.1 mm so they will be
fine in bright sunlight, but somewhat limited at dawn, dusk, or cloudy
conditions. You will still see the bird, but lose detail and color.
Ever wonder why birding standard binocs are 7X35, 8X40 (or 42 rather than
40) -- its that old 7 mm exit pupil thing. The higher price and higher
power 10x40 are a compromise in exit pupil which is compensated for by the
magnification, and the quality of the optics.
Lets now talk about close focus. Do you ever look at butterflies?
Tom
Tom Krakauer
Bahama, NC
tkrakauer@mindspring.com