Binoculars

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Observing with Binoculars

Beginning astronomers often believe that a telescope is essential for astronomy. In fact, many amateurs produce scientifically useful observations using only binoculars.

If you are a beginner, it is certainly wise to make a start using binoculars in order to become familiar with the night sky, before moving on to telescope observations. You may be surprised how much you can see.

If you get a good pair of binoculars, they should last a lifetime.

Types of Binoculars

Opera Glasses

These are not suitable for astronomy, except perhaps for observing the Moon or the Milky Way - but only if you haven’t got anything else more suitable.

Porro Prism Binoculars

The traditional ‘W’ shaped binoculars (see diagram below). They contain Porro prisms named after the Italian optician who invented them in the 1850s.

This type of binocular is generally the best for astronomy.

Roof Prism Binoculars

The design is like putting two small telescopes side-by-side (see picture below). They are more compact than porro binoculars. Cheap roof prism binoculars are not recommended for astronomy use, as they may not work well in low light.

Image Stabilizing Binoculars

These are a good alternative to porro, if you’ve got the budget. I highly recommend image stabilizing binoculars because they are so easy to use. They don’t require any support because they automatically correct the image to remove any binocular wobble. However, they are heavier than standard binoculars and do require batteries.

Giant Binoculars

These are specialized astronomical binoculars, often used for comet spotting and supernova seeking. They have a very large aperture and are really more suitable for the more experienced observer.

Binocular Buyer’s Guide

Good optical quality is a very important consideration when buying binoculars.

Remember that you generally get what you pay for. In most cases the brand name tells a lot about the quality of the instrument, so avoid buying from companies with which you are unfamiliar.

Size and Power

You will have noticed binoculars are described with two numbers - for example 7 x 50 - but what does this mean?

The first number - 7 in this example - is the magnification.

Now you might think that the larger the magnification the better. But really, as with telescopes, the aperture is more important. Too high a magnification will make the binoculars difficult to use without support.

The second number - 50 - is the aperture of the objective lenses.

The larger the lens size, the brighter the image you see. You need as much light as possible, so pick the largest objective lens diameter you can easily carry.

7 x 50 mm binoculars are ideal for beginners. They are great for general stargazing - they are lightweight, have a wide field of view and not much binocular wobble.

Many astronomers like to use 10 x 50 mm binoculars. This magnification (10x) is usually considered the most that can be held comfortably steady. More powerful, larger sizes can be used if you don’t mind carrying a tripod around. Alternatively, you can use a parallelogram mounting.

Lens Coatings

Try to get the best lens coatings you can afford.

Multi Coated is the most common coating system for affordable binoculars.

Fully Multi Coated is the best coating system. It means that every glass to air surface has multiple layers of coatings.

Avoid any binocular that uses "ruby" coatings. These are intended to reduce glare in bright light and improve the contrast between brown and green objects, however they perform poorly for astronomical use.

Eye relief

This is the distance at which your pupil should sit from a binocular eyepiece. If you wear glasses, look for eye relief of more than 14mm, or 17mm for thick glasses.

Type of Glass Prism

BaK-4 glass prisms tend to be brighter and better for astronomical viewing, but more expensive than BK7.

You really don’t need to know what these terms mean, but if you are interested, BaK-4 is made from barium crown glass and BK7 is made from a borosilicate crown glass. Crown glasses are so called because of the crown-like shape that is given to them after the process of blowing the glass.

bak4 (barium crown) is more expensive but works better. bak7 (borosilicate) is cheaper and doesn't work as well.

Diagram showing the design of a typical pair of porro binoculars.

A Typical Pair of Roof Prism Binoculars

What Can You See with Binoculars?

Binoculars have many advantages for observers - they are portable, have a wide angle of view and are easy to use. Certain astronomical objects like comets, open star clusters and constellations are easier to observe using a binoculars' wide field of view than observing with the narrow field of view of a telescope.

In dark skies especially, the view is breathtaking.

The Moon

You can get absolutely wonderful views of the Moon with binoculars. They make the Moon’s surface comes to life with its craters, seas and mountains. The view changes every night along with the Moon’s phases.

With binoculars, you can get an overall view of the whole Moon, whereas with a telescope you get a much more detailed, closer view.

The Moons of Jupiter

The Galilean moons of Jupiter are invisible to the naked eye but can readily be seen with binoculars. You will see how they change their positions every night.

Sadly, you won't be able to see any detail of Jupiter’s surface with binoculars. For this you will need a telescope.

You can see the larger moons of Saturn, the phases of Venus and, if you know where to look, Uranus.

Comets

Binoculars are great for watching comets. Large, powerful binoculars with their wide field of view are used by many amateur astronomers for finding new comets.

Star Clusters

The Pleiades, a lovely star cluster in Taurus appears as six or seven bright stars to the naked eye, but you will see many more stars with binoculars.

Nebulae

For example, the Orion Nebula.

Deep Sky Objects

Given dark enough skies you will be able to see deep sky objects such as the Great Spiral Galaxy in Andromeda.

Supernovae

Amateur astronomers are often the first to spot supernovae because they are using powerful binoculars that can scan a large portion of the sky.

Further Reading

Exploring the Night Sky with Binoculars by Patrick Moore

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