Binocular Collimation
All Models from 10x50mm to 25x100mm
A binocular is actually a pair of refractor telescopes joined together. The alignment between these two
telescopes is called "collimation". Proper collimation is critical to a binocular's performance, and the
user's viewing enjoyment. The brain can do a remarkable job of compensating for poor collimation, but
has more trouble doing so on the night sky due to the much lower amount of visual information. For
this reason, good collimation is especially critical for astronomical binoculars. Every binocular is
thoroughly examined, tested, and collimated before shipping to our dealers and customers. But
because collimation is occasionally lost due to rough handling during shipping, or from accidents
(dropping the binocular), we are providing instructions for collimation here.
Surprisingly, collimation adjustment is
easiest to perform in daylight.
Collimation can be quickly be
checked by viewing an obect with
distinct horizontal and vertical lines,
such as a house, building, or fence,
at least 200 meters away. It is best to
do this outdoors, as viewing through
a window can cause distortion from
diffraction. Begin by focusing on the
object. Alternate viewing with the left
and right eyes by gently closing one
eye at a time. Alternate eyes about once per second. Relax your eyes as you do this so they are not
compensating for misalignment. Notice that the object will move somewhat as you alternate eyes. A
slight amount of horizontal movement (to the left with the left eye, and to the right with the right eye) is
normal, and is desirable. Excessive horizontal movement, or any amount of vertical movement (see
pic at right), should be corrected.
To check vertical collimation, look at
a distinct horizontal line, such as a
roof line, gutter, or fence rail. Slowly
move your eyes back from the
binocular until they are about 4
inches away, while maintaining the
view of the horizontal line in
eyepieces. Let your eyes relax and
focus more on the image at the
eyepieces rather than through the
binocular. Even a slight vertical
miscollimation will now be readily
shown as a difference in position of
the horizonal line (see pic at right).
Now that we can determine collimation problems, how do
we correct it? The secret is the porro prism adjustment
setscrews hidden under the rubber armor close to the
edge of the prism covers, as shown in the picture at the
lower right. Note that models without rubber armor have
setscrews in the same postion, accessible through small
holes in the binocular body. In either case, you'll need a
rather narrow jewelers screwdriver to adjust the setscrews.
For rubber-armored models, use the screwdriver to
carefully lift the rubber covering to reveal the setscrews. If
you don't stretch the rubber any more than necessary to
reveal the setscrews, the rubber will snap back to original
position when you are done. The setscrews may be rather
difficult to move, and some downward pressure may be
necessary to prevent stripping of the setscrew slot.
