How to Use Binoculars

The purpose of this blog is to enrich your perception of nature. I try to use all the tools available to me to work towards this goal: I talk to people on a daily basis, sell them stuff to attract birds to their yard, lead walks, give presentations, and when I can’t seize an individual’s physical attention I bombard the public at large with thousands of words and hundreds of pretty pictures via this website. But despite my faith in the efficacy of the written word, I have to admit that the single greatest tool I know of to promote nature perception is a pair of binoculars.

Consequently, I’m always glad to see someone come into the store to get a pair, no matter whether she’s spending $70 or $500. Today I want to get more of our community’s extant binoculars into active use by explaining how to use these things properly, how to avoid common errors and frustrations, and how to tell if a pair of binoculars needs repair or replacement.

The case for binoculars in a nutshell

Now, given that I do derive a small but not inconsequential portion of my livelihood from the sale of fine two-barreled optical equipment, you might suspect that pecuniary motives incline me to overstate the case for binos. But consider the opinion of some people who are decidedly not commercial stooges:

March 13: Bought a telescope to-day for eight dollars.

April 23: Saw my white-headed eagle…We who live this plodding life here below never know how many eagles fly over us. They are concealed in the empyrean. I think I have got the worth of my glass now that it has revealed to me the white-headed eagle.

– Thoreau, The Journal, 1854

The leading voice of anti-consumerism in American history issued this rare product endorsement for a simple reason: good optics let you see things that were formerly invisible. This is no hyperbole; it’s a simple statement of fact for me to admit that all my heaps of words don’t match the value of seeing an eagle, a sight which is arguably inestimable and incontestably greater than $8, even in 1850s money (some $250 today – and binoculars far superior to Thoreau’s telescope can now be had for less than that).

One fan of binoculars...
... and another

You can get something usable for perhaps as low as $70 or so (but there’s a lot of terrible junk to wade through at that price). Or you can get something that’s really quite good and which will last you for the rest of your life for a few hundred dollars. That’s a very small price to pay to be permanently granted superhuman, eagle-like vision.

Sam: Why do you always use binoculars?

Suzy: It helps me see things closer. Even if they’re not very far away. I pretend it’s my magic power.

– Wes Anderson’s Moonrise Kingdom

It is a magic power Suzy.

Three steps to use them properly

So you have some kind of binoculars. Why are they uncomfortable, hard to focus, or otherwise disappointing in comparison with my extravagant claims? There are three things to understand about using binoculars:

#1 Set the eyecups depending on whether you are wearing glasses or not.

Twist up, twist down. Photo: Knives and Tools

There should be some kind of rubbery or plastic appendage that sticks out above the lenses of your binoculars – the eyecups. On most modern, decent binoculars this is a retracting circular frame that moves in and out about half an inch, usually by twisting. On older binoculars or on some crummy compact binoculars, there may just be a flexible rubber sheath around the eyepiece that you can fold outside-and-down to make protrude less.

What is the purpose of this? The eyecups exist to position your eyes at the correct distance from the lenses. If you are not wearing glasses, you should leave them in the extended, “out” position; if you are wearing glasses, you should turn them “in” or fold them down so that your eyes are not held too far away from the lens.

In normal use, you don’t want to be moving these up and down!

#2 Get rid of black spaces and achieve an image in one single circle.

See that circle of light? That’s what you need to line up with your eyes. (Note how small it is on compact binoculars too.) Photo: Ron Spomer Outdoors.

If you see two separate images or disruptive zones of blackness rather than a nice, single circular field of view, the cause comes down to one simple thing: the two barrels of the binocular are not lined up with your two eyes. Bend the center hinge of the binocular as you look through them, moving the barrels inward from the widest extreme until the two circles converge into one image smoothly and effortlessly. Achieving perfect eye placement will be harder if your eyecups are not properly positioned (see above), or if you have compact binoculars, which have a narrower shaft of light to align with your pupils.

If the images in the two barrels refuse to neatly cohere, it may be that your binoculars need repair – quite possible if they are cheap, old, abused, or have suffered a hard fall. See “checking alignment” below. Or you may simply need to adjust the diopter…

#3 Set the diopter for the variance between your two eyes.

This is the next thing that many binocular novices misunderstand. Your binoculars have one main focus wheel between the two barrels. Then they typically have a small, stiff-turning wheel by the right eyepiece, known as the diopter. This is to adjust for the difference between your two eyes. Set it once – if necessary – then don’t touch it!

A diopter on the right barrel. Photo:

So how do you set the diopter? First, decide if you need to do so at all. This small wheel might turn an inch or so in either direction, usually with the neutral center point marked with some kind of dot or dash, often between a plus and minus sign. Turn it to the neutral point, then look at something with your left eye only and focus with the main center focus wheel. Then switch to your right eye without adjusting the focus wheel. If the image through your right eye remains in focus, then your eyes are about the same and you can leave that diopter wheel in the neutral position and never worry about it.

If the right eye’s image is blurry, then we should take action. Look at your chosen object again with your left eye only, focusing only with the center wheel. When you have it as sharp as possible, switch to your right eye and now turn only the small diopter wheel – not the big center wheel. You should only need to move it a little to one side or the other (typically less than half an inch) to get your right eye image in focus. When it looks good, you should be able to look back and forth from your right to left eye with both images remaining in focus. From now on, just use the center focus wheel and leave the diopter wheel where it is – your binoculars are now set for your eyes.

Do the two images still seem off kilter and refuse to comfortable coalesce? Then let’s check alignment….

Three steps to evaluate your bins

Nikon Monarch 7 8×30 – lightweight and tough, this is the most popular binocular in our store

I hope your current binoculars are wonderful and fulfill all your hopes and dreams of what binoculars should be. But if they fall short of that beatific ideal of natural and effortless vision enhancement, it’s important to know that it is not your ideal that’s at fault – binoculars can be that awesome – but rather that your current pair is underperforming for a diagnosable and remediable reason. As Thoreau said: you’ve built castles in the air and that’s where they should be, now repair, purchase, beg for, or borrow the binoculars of your dreams. I’m paraphrasing a little.

#1 Check Alignment.

If you have a pair of binoculars already, but you are unsure of their condition or quality, the first thing to check is whether they are currently functioning as they are supposed to. Inexpensive binoculars will generally have an image that is darker and less sharp than a high quality pair, but even more critically they are often vulnerable to being knocked out of alignment by an impact. When we’ve tried to source really cheap binoculars (say under $50), we consistently found that around half of the binoculars would arrive at our store already misaligned – both quality control and the durability to withstand impacts were low.

This problem may be perfectly obvious: you may put your binoculars to your eyes and experience a profound, headache-inducing misalignment between the images of the two barrels. Or it may be more subtle, with only a slight misalignment that your brain is able to compensate for with some squinting and concentration, but which will make any extended use frustrating and uncomfortable. Your binoculars should not give you a headache!

To check the alignment, you can perform what’s known in the biz as a “horizontal line test.” Find a nice horizontal line to look at, like a shelf, a wire, or the top of a fenceline. Focus on it as well as you can, then gradually move the binoculars a few inches away from your eyes to the point where a small gap appears between the two now separate images of each barrel. Now look closely at your horizontal line – does it continue straight across, merely with a gap in between the two images? Or does it take a “step” in between, with a discontinuous jump between two vertical levels?

The line should look like this…
… not like this.
Images from the useful

If your binoculars have that “jump” in the line, they are out of alignment and need to be repaired. Most decent binoculars can be fixed by the manufacturer, often at no charge: search for “Nikon binocular service” or the equivalent based on the manufacturer of your binos and find out what the manufacturer’s repair policy is. But if your binoculars cost less than $80 or so, this may be fruitless and it is probably time to look for a new pair anyways.

#2 Choose a good size.

Assuming your binoculars pass the horizontal line test and are basically functioning, why else might your current pair cause dissatisfaction and be ripe for a particularly gratifying replacement? One of the most common obstacles to happy binocular use is inappropriate size. Binoculars are generally classed in size according to the diameter of the objective lens (the lens away from your eye, where the light comes in). This is the second number usually printed somewhere on the binocular: in an 8×25 model, for instance, the 8 indicates the level of magnification (it makes things look 8 times closer) and the second number indicates the diameter of the objective lens in millimeters. Let me lay out the simplified spectrum of binocular sizes for you:

Stick with the middle two. Photo: Well Travelled Mile.
  1. Compact: <30mm Really compact binoculars with a 20-something millimeter lens size have some definite downsides. The shaft of light you are trying to align with your eyes will be very narrow, meaning that comfortable eye placement will be more difficult and finicky and your image will be darker. Avoid these unless you absolutely need a really tiny size or must spend less than $100 (and even in compacts I haven’t found a decent one for under $60).
  2. Mid-Size to Full-Size: 30mm – 42mm There is still a range of sizes within this central sweet spot. A 30 or 32mm binocular will be reasonably small and not too heavy, while still being brighter and more comfortable to use than a little compact. 42mm is the standard full-size most common today and gives a brighter image in low light conditions, but some people may find some 42mm binoculars a bit heavy.
  3. Oversize: 50mm+ Now, a lot of optics makers sell 50mm binoculars and don’t consider them “oversize.” But generally speaking, such big binoculars are excessive and uncomfortable for most people. They allow you to use a higher magnification (such as 10x or even 12x) in low light conditions while maintaining a useful brightness level. But they’re just too heavy! There’s probably a reason why most 50+mm binoculars seem to be marketed towards hunters with pictures of lots of guns and unshaven men wearing camo gear. Avoid these too, unless your testosterone levels demand it.

#3 Choose a good level of magnification.

Leica 7×35, very classy. Unfortunately, not currently available.

Similar to this last mentioned marketing push for big binoculars is the marketing-fueled impulse towards higher magnification binoculars. Here, the sensible route is even clearer: get 8x or 10x. Anything higher will be hard to hold comfortably steady for an extended period (that’s why telescopes need a tripod), will have a narrower field of view, and will result in a darker image.

6x, 7x, or 9x are all perfectly reasonable too, but you unfortunately don’t see them as often due to the inelegant tyranny of market demand over mass-produced goods. I consider someone bearing a pair of 7x binoculars to exude a certain air of refinement, self-knowledge, and the well-grounded confidence of a man of the world, immune to hype and hucksterism. I use 10s because I have the arrogance of irreverent youth – relatively speaking – but even I wouldn’t go higher than that and I very well might grow out of them.


There you have it. If you have some decent, working binoculars, you’ll get the best use out of them if you:

  1. Set the eyecups depending on whether you’re wearing glasses or not.
  2. Adjust the barrels to match the distance between your eyes.
  3. Set the diopter – one time only – to correct for variation between your two eyes.

If you’re not sure whether your binoculars are decent and working (as opposed to either “crummy and ill-functioning” or “slatternly and unemployed” – neither is good), you should:

  1. Check the alignment of the two barrels, performing a horizontal line test if you’re not sure.
  2. Choose a pair that is a reasonable size – not too small and finicky to easily align with your eyes, but not too big and heavy to hold comfortably.
  3. Choose a pair with a reasonable level of magnification – don’t be mislead by the “bigger is better” illusion into magnifications greater than 10x.

If you are still unsure of whether a better pair of binoculars would indeed enrich your life, then I encourage you to join a free public birdwalk. A friendly request to take a look through someone else’s binoculars will rarely be refused, or if you join me on a Wild Birds Unlimited walk, we always bring a few loaner pairs which you are welcome to use for the day. If I have convinced you of the merits of an upgrade or new acquisition, then my natural counsel is for you to come into our Novato store and allow us to open up first our binocular case, and then a whole new world of unimagined marvels.

Header photo: Elegant shot of some guy with binoculars by Edith Soto on Flickr.

One Reply to “How to Use Binoculars”

  1. Well done, Jack! This is an excellent, clear introduction & overview for those of us who are novices to higher quality optics.

Leave a Reply