Binoculars Buying Guide

In order to know how to buy binoculars, you'll need to know a bit about how binoculars work.

The basics of binoculars

Prisms: When you look through a telescope, you see objects upside-down and backwards, which is fine for objects in space, where there is no up or down. Binoculars contain prisms that flip the axis of objects over to the way you would expect to see them down here on earth, "right-side up." There are two types of prisms, roof and porro, and each type affects the size and shape of the binoculars.

• Porro prisms: create a brighter, more realistic, three-dimensional image, which is better at night, making them preferred for astronomy. These binoculars have an offset design which makes them larger and heavier.
• Roof prisms: are smaller and straighter, so the binoculars are more compact and portable. Some of these compact binoculars weigh as little as 9 ounces. Roof prism binoculars can be waterproof or water-resistant. Roof prism binoculars tend to be more expensive because smaller prisms are more difficult to grind.

Objective lens: is the outermost lens, the lens that is closest to the objects you are looking at. The objective lens is measured in millimeters, and the larger the objective lens, the more light the binoculars let in and the brighter the image will be.

Magnification: is a measurement of how much larger an object appears, given with a number followed by an "x," such as 7x or 12x. Larger magnifications let you see less in your field of view, but the objects you see will appear closer. Larger magnifications can also make it harder to hold the binoculars steady enough to focus; use a tripod for anything over 10x.

Aperture: is given in the description of all binoculars. It tells you the magnification and the objective lens diameter. For example, 7x35 magnifies seven times and the objective lens has a 35 mm diameter. In general, these apertures will be appropriate:

• Indoor concerts, theaters and sporting events: about 6x30 (sometimes called opera glasses)
• Hiking and nature walking: about 7x25
• Outdoor concerts, sporting events and general purpose: about 7x35
• Astronomy, hunting and birding, target shoot: about 7x50 or 8x40

Eyepiece: is the part you look through.

Eye relief: is the distance between the eyepiece and the user's eyes. Eyeglass wearers should choose a long eye relief, at least 13 mm. Some binoculars have an adjustable eye relief for multiple users, using methods such as rubber eyecups which fold back.

Inter-pupil distance: is the distance, in millimeters, between the two eyepieces. The distance between the average person's pupils is between 60 mm and 72 mm. Make sure you choose binoculars that will adjust to your size. You can have someone measure the distance by looking straight forward and using a ruler.

Exit pupils: are the beams of light that exit the eyepieces and hit your pupils; these help determine brightness; larger exit pupils let in more light. Divide the diameter of the objective lens by the magnification to find the size. For nighttime use, you will want a larger exit pupil, around 7 mm.

Focusing methods: allow you to focus on an object.

• Many binoculars focus with a central knob to adjust both sides at one time.
• Some binoculars have a fixed focus, also known as "focus free," so they will not have a focusing knob.
• Other binoculars will have a diopter on one barrel of the binoculars, so you can customize the view through each eye.

Other helpful binocular features

Once you know your basic binocular needs for your intended use, look for some of these other features which may be helpful.

Lens coatings: are thin layers of chemicals applied to the glass surfaces in binoculars. Coatings on glasses reduce glare and light loss. The number of surfaces coated is specified at four different levels.

• Coated lenses: are the basic, least expensive binoculars. Only some of the glass surfaces are coated.
• Fully coated lenses: are more helpful than coated lenses and are good for general use binoculars. All of the glass surfaces have been coated.
• Multi-coated lenses: are better for night use because they will let more light in. Some of the glass surfaces for night vision have more than one coat of chemicals.
• Fully multi-coated lenses: will give you the brightest, clearest images. All of the glass surfaces have multiple coats of chemicals on both sides.

Rubber armor: is the rubber coating on the exterior of binoculars. Rubber armor protects binoculars from bumps and provides a better grip.

Fog-proof binoculars: are filled with nitrogen gas to give them anti-fogging qualities, making them perfect for use in damp environments, such as on a boat.

Zoom: allows you to change the magnification of the binoculars when you need just a little closer view. Some zoom binoculars only range between about 7x and 12x while others range as much as 10x to 30x. Zoom binoculars are often not as durable as regular binoculars, but they offer more options for casual users.

Binoculars care

To protect your binoculars, always use the neck strap or a tripod to prevent dropping. When you are not using your binoculars, store them in their case. Many binoculars will come with a non-abrasive cloth for wiping the lenses, similar to one used for eyeglasses. Binoculars should last you many years with just a little protection.

As your binoculars age, they may not be able to focus using the knobs, and they may need to be collimated. Collimation is the alignment of optics. If your binoculars have prism tilt screws, you can collimate your binoculars with a small screwdriver. Very carefully and gently tighten the prism tilt screws until the exit pupils are both perfectly round. Collimation is a very precise thing, so you may want to contact a local hobby shop to find a professional in your area to collimate your binoculars for you.

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