How to Choose Binoculars for Birdwatching

Selecting Birding Optics Balancing Cost, Weight and Perfomance

May 27, 2009

Birdwatching demands a lot of optical equipment, and the need to take them out into the field means weight is an issue for many people too.

Binoculars, or bins as birding folk usually call them, are the first essential tool any birdwatcher needs. There is a wide variety in price and styles of binoculars, and here are some tips in what to consider and what to look for.

Regardless of the cost, it is essential that prospective purchasers try out the binoculars they are considering. People's grip and vision differ subtly, and bins which suit one person's hands and vision may not suit another person's. Things like grip, weight and handling can be tested on an example of the model of binoculars, but when purchasing binoculars from a store it is best to try out the particular item that will be purchased, as there is some sample variation between different copies of the same model, particularly at the low end.

Low-Cost Options for Birders on a Budget

Birders on a budget, or those looking for their first pair of bins should look at models that follow the traditional stepped porroprism design (see below for details). This design offers fewer technical challenges for manufacturers, so optical performance at a given price point is usually better. On the downside, these are usually a little bit heavier than roof prism designs, and it is hard to make a porro design waterproof, though they can be made to handle normal showers easily enough.

Roof prism designs can be made waterproof and if more money is thrown at coping with the more complex internal optical path they can match the performance of porroprism designs. So if money is not so tight but getting the weight down is more important then roof prism bins come into their own. The top end bins from the likes of Swarovski, Leica, Zeiss and Nikon are usually roof prisms.

Things to Look For in a Binocular for Birding

Look though the bins, and adjust for maximum sharpness in the centre. Then look at how sharp the edges of the image are. High-contrast sharp edges, say a wall against the sky can show issues like colour fringing. This is usually blue on one side of the edge and yellow on the other, and is the hallmark of cheap optics, blurring details. The amount of detail in the shadows indicates how well the bins avoid spilling light from bright areas into dark areas. Moving the binoculars slowly side to side scanning the field of view should not show the scene warping unevenly as the bins are being panned.

Bins with a higher magnification inherently have a narrower field of view, but this is also affected by the design; reverse porro compacts can give a very narrow 'looking down a tube' field of view. Beginners often find it hard to locate a bird with binoculars, so a wider field of view is helpful even if it means using a lower magnification.

Binocular Styles - Traditional Porroprism and Roof Prism

Binoculars come in two main variants. One is the classic style, where there is a step in the binocular tubes looking from the eyepiece (the part the user looks through) to the objective lens (the larger lens that is pointed at the bird). This is a tried and tested design, called Porroprism or Porro for short. Usually the objective lenses are spaced further apart than the eyepiece lenses, but compact binoculars sometime have the step going the other way so the objective lenses are closer together than the eyepieces.

The second type is where the binocular tubes are in a straight line, and the distance between objective lenses is very similar to that of the eyepieces. This is called the roof prism design.

Binocular Specs

Binocular specs are cited as two numbers separated by x, for example 8x20 or 10x42. The first number is the magnification, the second is the size of the front objective. Greater magnification makes it harder to hold the binoculars steady and lowers image brightness, all other things being equal. For beginners a magnification of 7 or 8 is about right. The larger the second number the brighter the image is in theory, but the binoculars get heavier and bigger, and as the pupil narrows not all that glass will be used efficiently. Popular choices for full-size bins are 8x40, and 8x32 for pocket models, but some birders prefer 10x40. The only way to decide is to look through some models at some real world objects - specmanship is a bad way to choose birding binoculars.

The copyright of the article How to Choose Binoculars for Birdwatching in Bird Watching is owned by Richard Mudhar. Permission to republish How to Choose Binoculars for Birdwatching in print or online must be granted by the author in writing.