From: tchau@athena.mit.edu (Terry Chau)
Subject: Re: Binoculars Question
Organization: Massachusetts Institute of Technology
Date: Mon, 25 Jan 1993 15:46:00 GMT

In article <1993Jan24.184101.27715@thunder.mcrcim.mcgill.edu>, mackenzi@McRCIM.McGill.EDU (Paul Mackenzie) writes:
|> 
|> I assume there must be some people in this group who know about
|> binoculars - can anyone tell me what the numbers listed with
|> a particular unit mean?  I've seen a few in stores that say
|> 8 x 40mm or something like this, and I've also seen things like
|> field of vision is 340' at 1000 ft.  Can anyone tell me how to
|> decipher the magnification out of these so I don't buy a cheap
|> pair of field glasses?
|> 
|> Thanks,
|> Paul

The first number is the magnification, and the second number is the diameter of
the objective lens in millimeters.  The wider the lens, the more light it can
collect, and the brighter the images.  So 8 x 40 simply means 8x magnification
with 40 mm wide lens.

I suppose that the higher the magnification, the better for birding.  Usually high
magnification comes with wide lenses, plus weight and the cost goes up. 
 The monster binoculars go up to something like 20 x 100.  I think
they're mostly used for astronomy.  Are they too unweildy for birding, anyone?

I have a pair 10 x 50 Bushnell binoculars w/ Insta-Focus.  It's good 
for astronomy, and it's really great for birding, too.  It's not too heavy, but it
is a little tiring if you hold it up for a long time.  It's no big deal though.  I
bought it a few years ago for about $60.  Most high quality 10 x 50 binoculars go
for about $200.  Even good 7 x 35 binoculars go for $100 plus.
My $60 binoculars is good enough for me.  In my case, I would
rather spend money on a spotting scope instead of replacing my binoculars for a
better $200 one.

In other words, the less expensive models are sometimes good enough.  Unless, you
are highly perceptive and notice the less-than-optimum optics, or if you have the
money.

Before you buy a new pair of binoculars, it's a good idea to test them out.  For
example, you can look through the binoculars a foot away.  The circle of light
should be centered in the eyepiece lens.  If you look at a horizontal line, it
should also look horizontal through the binoculars.  If you look at a white wall,
it should look white through the binoculars, not yellow or blue or whatever.
  Just make sure that there are no
grossly misaligned optics, and scratched lenses.  Just a precaution.

However, that 340' at 1000 ft, I can't tell you about.  I read it somewhere, but
I forgot about it.  Someone else?

Field glasses are a little different than binoculars.  These were around before
prisms were used, which made binoculars much more compact than field glasses.
  Field glasses were two telescopes mounted side-by-side.  So
they turned out to be more than one feet long.  Very unweildy.  It might be nice to
have in your home though.

Does anyone know if there is a big difference in the image quality between a $60
binoculars and a $200 binoculars?  I haven't tried out the more expensive models.
Maybe I'm too complacent with my own pair of $60 binoculars.


-- Chau  
Newsgroups: rec.birds