[Leica] Binocular selection

[Holger Merlitz <merlitz@int.fzk.de>]

In a recent thread initiated by Javier Perez the pro
and cons of certain binoculars were scratched. Needles
to say that there exists a huge spectrum of binoculars
with all kinds of features on the market, and it is
easy to spend 1000 of $ and still get the wrong one.
Allow me to share a few observations I have made with
binoculars:

First of all, aberrations are not as much a topic as
they are for camera lenses. The image in a binocular
will not be recorded and blown up to poster size - you
see a life image, which may be shaking in your hands,
so that parts of the microstructure are lost anyway.
Distortion can be annoying, however. A good coating is
mandatory, so that ghost images are quite common in
some cheaper models, and you will prefer to have a wide
angle of view and robust mechanics - these are important
features of a binocular.

If someone asks me which binocular to buy, I will first
of all find out what it is going to be used for. This
will set the range for the magnification. The general
rule is: Do not go for higher magnification than
neccessary. 10x is about the limit which can be hand-held,
and a tripod would spoil the mobility of the device. Image
stabilization is a possible solution, but expensive and it
could make you depend on batteries (the Zeiss IS does not
need batteries, however the price of the 20x60 may be
around 4000$).
For cruising around in the mountains, 6x is already fine,
for observing birds 10x is useful, to enjoy craters of
the moon and the rings of saturn, 20x is more adequate.
If you need a high magnification, you will need IS or a
tripod. But you may then also consider to get a telescope
instead.

Next question is: Is it to be used during bright daytime
or also in twilight (e.g. for hunting)? The diameter of
the objective lens will determine the amount of light
entering the device, and also its weight, of course. The
exit pupil (ep) diameter can be evaluated using
ep = (Objective diameter)/magnification
For twilight use, it should have at least 5 mm, but once
it is larger than the pupil of the human eye, light is
wasted, which leads to a limit of 6-7mm depending on the
individual who is using this binocular (elder people
usually have a smaller pupil size).

Is the binocular to be used in tough conditions? In this
case, military devices are adequate because they are
obviously quite rugged (beware of those faked 'military
look' binoculars).

I do not quite agree with Marc James Small that one has
to spend two or three times of 500 $ for a decent binocular.
I am using a DF 7x40 of the East German NVA which was
produced by Carl Zeiss Jena and is available on e-bay for
150$ (good condition). This one is lying in my hands as if
it were glued to, giving a bright and steady wide field
image. Its mechanics  appears undestroyable. If you spend
1000$ or more, you will surely get quality, but it is
possible to get it for less.

Here, someone has tested many binoculars for astronomical
applications:
http://www.weatherman.com/BINOCS.HTM

These kind of tests are quite selective, because astronomical
objects are often pointlike and bright so that aberrations
and reflexions become easily visible. Alltogether I think
Leica has no outstanding position on the binocular market.
Others are similarly good and usually cheaper. First of all,
however, find out what you really need it for and then spend
as much money as necessary to satisfy your needs.

Holger Merlitz,
Karlsruhe
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