If you’ve ever looked through a supposedly good pair of binoculars and said “blehh,” read on.
We recently finished with CMBO’s Annual Optics Sale, during which more than 100 happy people walked away with more than 100 high-functioning pairs of binoculars and/or spotting scopes and tripods. A whole lot of looking through binoculars happens during these sales, and the staff works hard to make sure customers find the right glass to make their birding as fun and effective as possible.
All the binoculars at the sale were birding worthy (some more than others), yet now and then I’d pick up a pair to check it for a customer and find a fuzzy image on the receiving end, as if something was wrong with the binoculars. This happened with cheap binoculars and expensive ones, and, the truth is, it sometimes happens with my own bins, too.
It’s the dipoter that does it - that essential but sometimes annoying individually adjustable right eyepiece put on binoculars to allow a one-time, permanent adjustment for the difference between the observer’s left and right eyes. You can’t ignore the dipoter, and trying to use a pair of expensive bins with the diopter out of whack will be all the proof you need of that.
Here are some tips for living happily with your diopter, and hence your binoculars:
1. The first thing you should do when you pick up binoculars is check the diopter setting. On some binoculars, the diopter comes in the form of a rotating right eyepiece; on others, the mechanism for adjusting the right eyepiece is incorporated into the center focus. Check the instructions that came with your binoculars, or stop by CMBO, we’ll be happy to help you figure it out.
2. When using unfamiliar or new binoculars, first set the diopter to the neutral center setting, normally indicated by a “0” or a hashmark centered between “+” and “-“ marks, and leave it there while you become familiar with the bins.
3. After you are familiar with the bins (unless your left eye and right are wildly different, I usually suggest birding with them for a day or two first), you are ready to set the diopter. When adjusting the diopter, pick a sign or other stationary object with print on it 40-50 yards away to focus on. Cover the right barrel with your hand, and adjust the center focus of the binocular until the print is clear through the left barrel. Then, carefully avoiding any change to the center focus, cover the left barrel and slowly move the diopter adjustment back and forth until the print is clear through the right barrel.
When the print is clear in both barrels, check the diopter setting and leave it there. From now on, the only focusing you’ll do will be with the center focus – or it should be, were it not for some diopters’ annoying tendency to adjust themselves. So each time you pick up your bins, check the diopter to make sure it’s set where it’s supposed to be. And it’s a good idea to check the diopter setting on your binoculars every now and then in case your eyes have changed.