Binocular Advice

Binocular Recommendations

Almost any pair of binoculars about $250 or more should prove satisfactory in optical quality and craftsmanship for lifelong terrestrial and celestial use. Try to buy locally in order to find a pair that fits comfortably in your hands—this is important.

Diameter of objective and magnification. Purchase a pair that can be used for both astronomical and daytime adventures: 7x40, 10x40, 7x50 or 10x50 are good choices. The first number indicates the magnification while the second number indicates the diameter of the front lens in millimeters. A 35mm lens or smaller is a little too small for astronomical use. Those with magnifications above 10x are difficult to hold steady and require a tripod for best use. Avoid buying binoculars with a number starting with 11 or higher.

Optical design. Both roof- and porro- prisms are good designs. Roof-prisms are more compact (and look “cooler”), more expensive, heavier and less comfortable to hold. Overall, porro-prisms are the best deal for the money and the most comfortable to hold. See pictures at right and below.

Tripod consideration. For exploring the heavens, a camera tripod will help immensely to steady the view and eliminate arm fatigue. However, this is an item you can purchase at a later date.

Warranty. Some companies offer a life-time alignment warranty, however, choose a major company that you think will be around 20 years from now.

Return policy. Inquire about the return policy, especially if you purchase online and/or as a gift because not all binoculars are comfortable to hold in your hands.

________________________

Great Telescope Stores. Click here for a list of great telescope stores across the US that also sell binoculars.

Want Advice? If you have a question or would like advice on buying a telescope, binoculars or accessory, please email me (Ken Graun) at AstroInfo. No charge, no obligation, no hassles.

The lenses of most binoculars have special coatings to increase light transmission. Coatings produce color casts of green, blue and purple as can be seen from these lenses (some are orange, too). Although coatings are lasting and durable, care must be taken when cleaning lenses because they can be scratched.

Binoculars are classified by their magnification and front-lens diameter. This pair is a 10x50, which is indicated on the focusing knob. 10x is the magnification and 50 the diameter of either front lens in millimeters.

Binoculars

Although most of us want a telescope for observing the heavens, I rate binoculars excellent as an instrument for celestial exploration. They offer the comfort of two-eye viewing and capture greater vistas than is possible with telescopes. And, since many of us already own a pair of binoculars, we can use them to go out and start observing right away. Today, almost all middle-of-the-line binoculars, ranging in price from $250 to $350, offer good optical performance.

Binoculars add a dimension to observing that cannot be achieved with telescopes. In my opinion, the most beautiful sights of the Pleiades and the Praesepe come through binoculars. These clusters fill the binoculars’ field of view and give the impression that the stars are floating in front of you.

Classification of binoculars • 7x50, etc.
The magnification and lens diameter of binoculars are designated by a pair of numbers with an “x” between them. A few examples are 8x20, 10x40 and 7x50 (7x50 is pronounced seven-by-fifty). Generally you will find this description somewhere on the binoculars. The “x” actually belongs to the first number and signifies power, while the second, larger number is the diameter of either front lens in millimeters.

Comparing binoculars for astronomical use — Using that little “x”
The Royal Astronomical Society of Canada has come up with a useful “measure” for comparing the astronomical performance of binoculars. This measure involves simply multiplying the magnification by the lens diameter to obtain a comparison number called the “Visibility Factor” (e.g. 8x20 = 160). Higher numbers indicate better performing binoculars for astronomical use. According to this formula, and verified by field use, some smaller lens diameters can perform as well as those with larger diameters (10x40 = 400 compared to 7x50 = 350). This Visibility Factor can be most helpful when you are choosing from a plethora of similar binoculars —the one with the highest value will be best for astronomy.

Other considerations when purchasing binoculars

Roof prisms vs. Porro prism binoculars
Both (types) of these binoculars perform well. The roof prism binoculars look like two straight tubes next to one another. The porro prism binoculars look more “traditional,” having eyepieces offset from the front lenses. Roof prisms are usually more expensive because the tolerances for their internal prisms must be higher in order to achieve good imagery—BAK-4 prisms are the standard quality for these units. They are also more compact, which may be an advantage for traveling.

Magnification limitations
Binoculars usually provide just one magnification, generally ranging from 7x to 10x because they are designed for hand-held use. Some binoculars have zoom capability, but most amateur astronomers avoid these because their optical quality is sometimes not as good as units with single magnifications.

Viewing comfort and eyeglasses
Binoculars should be comfortable to look through. The “eye relief,” of eyepieces, controls viewing comfort because it determines the distance you must place your eyes from the eyepieces in order to take advantage of the full view provided by the optics. Generally, but not always, higher magnifications mean less eye relief. It is always a good idea to try binoculars before you buy to make sure they are comfortable to look through. If you must wear glasses, binoculars with short eye reliefs may be difficult to use. Many binoculars have rubber guards that either fold back, push or twist in/out to accommodate eyeglass wearers.

Comfortable ergonomics
Some binoculars are more comfortable to hold than others. Although this may not be an immediate concern when using binoculars in conjunction with a tripod, it will become one for daytime and casual use.

Multi-coated optics
Binoculars incorporate a number of lenses and prisms. Special coatings on their surfaces help to increase light transmission tremendously. Although it is difficult to tell if the interior surfaces are coated, the exterior front lenses and eyepieces should show a distinct green or bluish-purple cast (even orange), indicating that these surfaces are coated. Binoculars with multi-coated optics tend to look dark when you peer into the front lenses. Many binoculars are inscribed with the words “Multi-Coated” on their exterior, but there is no industry standard definition of this term.

Field of view
One of the greatest advantages of binoculars over telescopes is that they let you see a large area of the sky at once. Some binoculars even feature extra-wide fields of view; however, I would avoid these for astronomical use because the stars around the edges of their fields of view often appear out of focus.

Large, high-powered binoculars
If you really like binoculars for astronomical use, but want more power, there are large binoculars like 15x60, 17x70, 20x100 and others that might interest you! Obviously, these large instruments require sturdy mounts and tripods.

Tripods

Attaching your binoculars to a camera tripod is very helpful when exploring the heavens because it steadies your view and eliminates arm fatigue. You can also lean on the tripod, which makes it easier to stand in one spot for a long period of time.

There are also specialized parallelogram-type binocular mounts that are particularly useful with groups because they keep an object in view even when the binoculars are moved up or down to accommodate individuals of different heights. Parallelogram-type mounts can be used when standing or adapted for sitting and reclining positions.

Today, most binoculars come with a tripod socket that allows attachment to a tripod head; however, you need to purchase an adapter. Many older binoculars don’t have sockets, so you may have to get creative to latch these down.

Aiming towards the sky
Binoculars are easy to aim during the day, but they are much harder to aim at objects in the night sky. The bright stars are not a problem, but areas where there are fainter stars can pose difficulties. For this reason, many amateurs attach small reflex-sight finders to their binoculars to facilitate aiming (You might have to get creative in attaching the finder to the binoculars.). These finders project red dots onto the night sky. Most reflex-sights can be removed so the binoculars can be stored in their case.

ABOVE. Porro-Prism Binoculars

You may already have a pair of these binoculars lying around, so observing the sky is just a matter of finding them and stepping outside. Porros are a proven design identified by the offset of the eyepieces from the front lenses. They are also very comfortable to hold. Although this design is bigger and thus bulkier than roof-prism binoculars, it can edge out the performance of roof-prism binoculars at a lower cost.

BELOW. Roof-Prism Binoculars

Nature lovers and hikers often prefer this type of binoculars because they are compact in comparison to porro-prism binoculars; however, they are usually more expensive. Although these binoculars look like two small, side-by-side refractor telescopes, they incorporate several internal prisms to provide upright imagery. Quality roof-prism binoculars perform just as well as porro-prism binoculars.

Tripod adapters are used to attach binoculars to tripods. Note: Not all adapters will fit the tighter barrel constraints of roof-prism binoculars.

Parallelogram-type mounts are great for groups. The binoculars stay on target even if moved up or down to accommodate different height individuals. Note the reflex-sight finder on top of the binoculars to aid in pointing.

What’s Out Tonight? is sponsored by Ken Press, publisher of astronomy books and charts.
Phone: (520) 743-3200 • Fax: (520) 743-3210 • Email: ken@kenpress.com