Binoculars and Spotting Scopes

SDOS Buyers guide to making a choice

Preamble

A pair of binoculars is a necessity for birdwatching unless the birds are unusually close but a telescope is an optional extra and, if you are starting out, a telescope purchase might be delayed until you are certain you want one. 

Binoculars are relatively light in weight and well suited to short to medium distance bird watching. Telescopes are needed for longer distance and for detail on distant birds, but are relatively heavy and bulky, and need a tripod, so carrying one about is a commitment. Telescopes are well suited to the wide-ranging views of open country and river estuaries but much less useful in thick vegetation or forests.

There have been recent advances in high quality mini – telescopes but a tripod is still needed because it is virtually impossible to hand hold a telescope. 

Tripods can be much more idiosyncratic than telescopes and a tripod that suits you (and the telescope), in terms of its operation, is something to focus upon when making a telescope purchase. 

The marketplace for birding optics has changed markedly in recent years as relatively cheap binoculars and telescopes from Chinese manufacturers have entered the market. Independent reviewers suggest that the quality of some of these products is good but sorting out what is available and whether it will suit you requires quite a lot of reading of reviews. There are many of these on the web and some represent reasonably independent assessments.

Basic choices

There are two birding variants of both binoculars and telescopes that can be considered at an early stage of decision making. 

Roof-prism binoculars are essentially two straight tubes connected by a hinge and each tube contains an objective lens (the bigger one at the front) and an eyepiece magnification lens at the rear. Between these two lenses a prism system corrects what would otherwise be an upside-down mirror image and a focussing lens brings the subject into focus. Because your two eyes are likely different there is a diopter adjustment that adjusts the focus mechanism to compensate. In a roof-prism binocular you look straight through each tube – another way of putting this is that the light takes a straight path through the instrument.

In porro-prism binoculars the objective lenses are further apart than the eyepieces and the prisms are arranged accordingly. Effectively this arrangement makes your eyes further apart so depth perception is improved compared to roof prisms. This is probably their main advantage. Porro-prism binoculars are wider, are often rather bulky, and some can be awkward to hold in smaller hands.

Roof-prism binoculars are robust and strong, they go out of adjustment less easily, they are less wide so are easier to hold in your hands, and they are also easier to make waterproof. There are many makes on the market at a range of prices and roof-prisms are the modern go-to choice for birding binoculars.

Spotting scopes have bigger objectives lenses to gather light than binoculars, and higher magnification eyepieces, so can deal with capturing detail over longer distances. They have essentially the same internal optical components as one tube of a roof-prism binocular but typically will offer a zoom lens as the eyepiece. The initial choice here is between an angled eyepiece where you bend slightly downwards to look into the telescope or a straight through eyepiece where you look straight through the telescope at eye level. Most birders nowadays choose angled telescopes because they are more convenient for a variety of reasons. Two examples of this convenience are that people of different heights can share them easily, and it is also relatively straightforward to look up at birds in the tops of tall trees using an angled telescope..

Choosing you instrument

Buying birding optics generally entails compromises and there is probably more complexity to the decision making than in the purchase of many other consumer durables. There are optical compromises associated with the physics of light transmission, weight compromises in terms of what you wish to carry about, and affordability compromises across, nowadays, a huge price range. The aim here is to enable you to understand what you are looking for and what optical performance you are likely to get. First to binoculars.

Binoculars

Binoculars are classified according to the ratio between their eyepiece lens magnification and their objective lens diameter. For example 8×40 is a magnification of eight times and an objective lens diameter of 40mm. Most birdwatchers will be using one of four variants:

8×30 – 8×40 – 10×30 – 10×40: there are small variations on this theme, for example 8×42.

Anything above 10×40, for example 12×50, is going to be heavy to carry around and difficult to hold steady. Binoculars smaller than 8×30 are not going to be great for birding, one problem is their relatively narrow field of view. 8×40 is the traditional choice and if you habitually bird with a telescope is probably the go-to option.

Lower weight and smaller size are the advantages of x30 binoculars. You will lose out in terms of light transmission in dull conditions, but this may not be a big disadvantage for many people when compared to the portability and handling advantages of smaller binoculars. 

8x binoculars have broader fields of vision and greater depth of field, 10x binoculars have greater reach, especially useful if you do not carry a telescope. 10x binoculars require more focussing action when used at short range; 8x cope better close-up in dense vegetation. 

In a nutshell if you are exploring bushes in dull November twilight looking for little birds then 8×40 is a good optical choice: if you are wandering miles over summer sunny uplands or desert plains carrying your binoculars, and looking at birds over a considerable distance, then 10×30 could suit you best. 

Telescopes

These are described by the same system as binoculars but the numbers are bigger. For example you might see 30Wx80 which is a 30x magnification wide angle eyepiece with an 80mm objective lens. Another combination might be 20-50Zoomx60, a 20-50 zoom eyepiece with a 60mm objective lens.

When using birding optics part of the time you are looking for birds and part of the time you are looking at birds. ‘Looking for’ is aided by a wide field of view, good depth of field and a bright image. ‘Looking at’ is favoured by magnification but you need sufficient light to see the detail. Zoom lenses on telescopes can deliver this combination well but the image gets darker as magnification increases so high magnification zooming works best with large diameter objective lenses. This in turn means a bigger telescope and more weight. 

Perhaps more so than with binoculars, with telescopes it is worth asking the question ‘do I really want to, or am I able to, carry all this about for a day’s birding.’ In bright light small scopes can do a good job.

Some practical considerations to look out for

Focussing, depth of field and breadth of field

Binoculars vary in their ability to close focus. This is not too important for birds but if you want to focus on butterflies or other creatures that allow close approach then it may be a consideration. Depth of field is related to focus and is the distance over which objects remain reasonably in focus either side of the focal point. A shallow depth of field entails more focussing activity.

Breadth of field varies between binoculars. It is the size of the observable area (a circle) at a known distance from the observer. Binocular reviews will mention this and use a standard distance to allow comparison between models. Importantly the image should remain in focus towards the edges of the field of vision. 

Waterproofing and filling with nitrogen

In the past some binoculars suffered from internal condensation in moist air. Modern binoculars are sealed and filled with nitrogen to avoid this. Binoculars will get wet and sometimes they get covered with salt that needs rinsing off, so look for a good weather proof performance. Some lenses now have external coatings that repel rain drops.

ED and HD glass

The best binoculars will transmit more than 90% of the input light. This is achieved through extra low dispersion glass (ED) and special coatings. HD glass has varying definitions and there is also no standard for ED glass. Read reviews that compare binoculars for guidance and look for characteristics such as brightness, clarity, good edge definition, and natural looking images. 

If you wear glasses

If you wear glasses some optics can work better than others. To achieve focus your eyes need to be placed at the correct distance from the eyepiece. This is done using moveable rubber eyecups. Telescopes are the same. If you wear glasses the rubber eyecup is retracted and your glasses fit against the retracted rubber eyecup. This, in theory, produces the same spacing between the eye and the lens as if you were not wearing glasses. In practice some binoculars work better than others for glasses wearers. Binocular reviews will generally consider this issue so it is worth checking out.

 

Making the choice 

Try before you buy

Binoculars are hand held and need to feel comfortable in your hands when held up to the eyes. You need to be able to operate the focussing wheel rapidly and do not forget the possibility that you will be wearing gloves in winter. How a pair of binoculars feels is essentially subjective but most modern roof-prism binoculars are fairly similar in terms of shape and balance. Porro-prism binoculars are more variable.

Telescopes sit on a tripod much of the time so how they feel is not much of an issue. Telescopes are focussed by hand with some sort of wheel device and there are varying systems to do that, probably none of which stand out as best. 

Most birdwatchers emphasise the importance of trying before buying. Outlets such as the RSPB shops and other optics suppliers have showrooms that allow you to handle and look through binoculars and telescopes but remember that you are not an experienced optics tester, and that many binoculars and telescopes will seem fine on bright, sunny days. Also remember to think about portability – even binoculars can seem heavy after a few hours.

Buying used optics

Buying second hand has been a traditional recommendation to obtain good optics but used examples of top of the range optics have a low depreciation rate, and, if you buy through a dealer, there is a profit margin also. Used may not be the cheapest way to get a decent pair of binoculars.

The breadth of choice in today’s market

There is now much more choice than 10 to 15 years ago and few outlets can stock the wide range of optics that are available through web ordering.

Realistically the only way through all this choice is to read as many reviews by experienced testers as possible before you head off to a shop with a shortlist. 

The website bestbinocularsreviews.com is an excellent starting point. It makes recommendations at various price points in the market from just over £100 to the high-priced European brands. There are some reviews of telescopes and there is also an excellent collection of commentaries that expand on some of the subjects touched on in this guide. One piece worth reading is just what you are getting if you buy a really expensive brand – how the instrument differs from a cheaper product.