from testing and always had a pair
of reference binoculars handy for
comparison.
Resolution Testing
To test optical resolution, we set
up a stable tripod with a beanbag
rest. Across the room we posted
a standard U.S. Air Force 1951
optics resolution chart that let us
translate the level of detail we
could see into a numeric score for
each pair of binoculars. We also
posted a dollar bill, the fine detail
and high-quality printing of
which made it
an ideal graphics target. A
ceiling-mount-ed halogen
floodlight provided consistent lighting.
Team Test Day
To help us get a wider perspec-
tive, we opened up our “laborato-
ry” to local birders (“Team Iowa”)
for a test day. We gave them access
to the same viewing conditions and
all the tools
we had set up
to compare
binoculars.
Their opinions,
comments, and
scores are integrated into the
chart and individual reviews.
We mounted
a 2x eyepiece
doubler behind
the binoculars
so we could
see the resolution not just at
A Few Caveats
8x but at 16x.
Murray Foster, Team Iowa 2010, selects another binocular to test.
Even resolution scores,
which we
measured carefully, can have a
margin of error.
The doubler effectively gave
us super eyesight and helped us
distinguish fine differences that
might be difficult to detect at 8x
magnification. Below the chart
we mounted a 4-foot ruler to
compare field of view.
The difference between 5.0 and 4. 8
may loom large on a chart, but such
scores are actually not far apart. In
the field, your eyes may not see any
difference.
We tested each model of
binoculars many times over an
interval of more than a month, and
we averaged the scores. To mini-
mize the effects of temporary eye
fatigue, we took frequent breaks
Another caution is that we had
only a single sample of each binoc-
ular model to compare, and it might
have been atypical. Variation in
quality is less likely with expensive
optics, as stricter manufacturing
tolerances are part of why they cost
so much. But you never know.
