“I have to take my glasses off to look through a binocular, right?” (I’ve lost track of how many times I’ve been asked this).
No. No you don’t.
In fact contrary to what you may have heard leaving your eyeglasses on when looking
through a binocular can give you a benefit non-wearers don’t have. So there—a rare
win for us “four-eyes.”
If you spend any time with other folks using binoculars (and I would certainly
recommend that you do) you’ll likely see this familiar scene: people wearing eyeglasses
are among a group of birders walking around with binoculars in their hands or hanging
around their necks, and…wait! What just flew into that tree? The eyeglass-wearers flip
their glasses on top of their heads, then look through their binoculars into the tree
(usually, hopefully, the eyeglasses don’t fall backwards off their heads).
Oh well, whatever it was we lost it.
Put the binoculars down and the glasses back on.
Me, I’m a lazy eyeglass-wearer, and I simply don’t want to do all that every time I use
my binocular. Not to mention that it’s unnecessary and often counter-productive.
Sure, we eyeglass-wearers may have to work harder at the outset to get the right “fit,”
paying special attention to the eyecups and a spec called eye relief (more about that
later) but it’s time well spent. And for most people you only have to do it once.
First, the eyecups: on all modern binoculars the eyecups adjust to accommodate the
viewing needs of eyeglass wearers. The rapidly-disappearing, older-style soft rubber
eyecups fold down for eyeglass use; the newer-style hard rubber-type twist down
(usually by rotating in a clockwise direction). The reason the eyecups need to be
adjusted is simple and brings us to the concept of “eye relief.”
Eye relief is the distance from the ocular lens (the glass at the smaller end of the
binocular, the end you look into), expressed in millimeters, that the eyes need to be to
see the full image with full field of view. If your eyes are beyond that distance you’ll only
get a partial view, giving you the “looking through a keyhole” experience.
So imagine that the eyecups of your binocular are in the default, “up” position. If you
look through the binocular without wearing glasses your eyes will be resting comfortably
on the outer edge of the eyecup, the depth of which puts your eyes (more or less) at the
ideal position for seeing the full view that nature (or rather, the manufacturer) intended
for that binocular, enjoying full field of view.
But look through the binocular in the same “up” position while wearing glasses and your
eyes are no longer in that optimal position—that’s where your eyeglass lenses are. Your
eyes are some distance away from that preferred position, and depending on a number of factors—how deep set your eyes are, the thickness and curvature of your eyeglass
lenses, among them—you’ll only see a portion of the image, making it more difficult to
focus on what you want to look at, and in the case of living things like birds, more
difficult to track movement.
Now with your eyeglasses still on, roll or twist down the eyecups, and rest the ocular
lenses gently against the surface of your eyeglasses. Assuming that the binocular offers
enough eye relief distance your eyes will now be in approximately the right position to
enjoy the same full image as non-eyeglass wearers. Plus the ability to gently rest the
ocular lenses against your eyeglass lenses allows you to stabilize the image (reducing
the “shake” from hand tremor) and also helps to diminish the hand and arm fatigue that
can happen when holding the binocular for long periods of time.
So there you have it—actual benefits of using a binocular with eyeglasses! Time to get that eye exam you’ve been putting off!
Most people who wear eyeglasses should enjoy a fantastic viewing experience with the
eyecups in the full “down” position (either rolled or twisted down). For some, however,
there will still be problems—most often an annoying dark “shadowing” effect around the
edges of the field of view. The fancy-schmancy term for this is “vingnetting,” but
whatever you call it it’s often caused by too much eye relief for the user, and very likely
a major reason why many eyeglass wearers ditch their glasses when using a binocular.
All is not lost, however. The twist eyecups on most modern binoculars can adjust, “click-
stopping” in several positions from fully-up to fully-down. So depending upon the
characteristics of your eyes and glasses you may enjoy a better viewing experience by
twisting up the eyecups to first “click-stop” position.
Yet another reason why it’s ALWAYS better to purchase your binocular in-person from a
knowledgeable optics salesperson rather than online. You should know that if you wear
eyeglasses there will be some binoculars on the market that WILL NOT work for you
and your glasses regardless of what you do. So once again having an optics expert with
you when you fit your new binocular to your eyes, glasses and hands will ensure a
lifetime of enjoyable use…or at least, long enough for you to trade up to your dream binoculars.