Whether you want binoculars for bird watching,
general nature study, sports,
there are a number of factors
- Magnification - How close the binoculars make a distant
object seem is called "magnification."
For example, magnification of 8X (often called
"8 power") makes an object 80 feet
away appear as if were only 10 feet away.
Is more magnification better? Not necessarily.
These is a downside to greater magnification:
Therefore for most purposes,
7X or 8X binoculars
are safer bets than 10X. Note,
field of view and depth of
field can vary
between instruments with the
based on the quality of manufacture.
- Hand Tremor - no one can hold binoculars
perfectly still. As magnification increases,
you are more likely to notice that the image
shakes. Windy conditions or on a boat (as
in whale watching) only increases the problem.
- Field of View - people with normal eyesight
have a field of vision that radiates roughly
160 to 170 degrees in both the left-right
and up-down dimensions. Most 7X binoculars
have a field of under 9 degrees, which shrinks
to about 5 degrees with 10X binoculars. With
a smaller field of view it becomes harder
to find an object, especially a moving one
like a flying bird.
- Depth of Field - people with normal eyesight
(or good eyeglasses) can look off in the
distance and see everything from a few feet
away to the horizon with roughly equal clarity.
With binoculars, once you focus on a distant
object, other objects more than a few feet
in front of or behind your subject will be
out of focus. At greater magnification, the
in-focus range usually becomes narrower.
Learn about other factors, such as size of
the objective lens, comfort, close focus,
weatherproofing, eye cups, and other qualities.