Optics guide

Pick up a binocular you are keen on testing, look through it and try running through the following evaluation process.

Bulk: does it feel well-balanced and comfortable to hold while you are looking through it? Can your fingers reach the focusing wheel with ease? Some models feature ëcut-awaysí or thumb-rests built into the undersides of the barrels to facilitate holding; if your binocular has these then check they are well-positioned for your hands. Consider how you are going to use and keep your binocular; do you want to carry it in your pocket, handbag or car glove compartment?

Weight: will you be able to hold it to your eyes for long periods of time without experiencing hand- or armfatigue? Is it light enough to carry around all day without causing neck-strain? If necessary, consider purchasing a neoprene-padded strap to spread the load and optimise comfort.

Eye comfort: the inter-pupillary distance is important, so vary the angle between the barrels via the central hinge until you can see an image comfortably ñ that is, no black shadowing in the centre or at the sides.The full field of view should also be visible, so vary the eyerelief by twisting each eyecup up or down until you find a position which gives you a full field. Some manufacturers build in click-stop mechanisms to lock your optimum cup position in place, while others may have fold-down rubber eyecups which can only be positioned either up or down, with no intermediate setting. Check that the full field is visible if you wear glasses; this is usually achieved with the cup in the lowest position. Check also that the eyecup material will not scratch your spectacle lenses.You will be spending a considerable amount of time looking through your binocular, so achieving comfortable fit to your eye is of paramount importance.

Focusing: ensure the central focusing wheel turns smoothly and freely, ideally with around one single rotation taking the image from close focus to long distance, at the same time allowing fine focus adjustments to be made.Taking many turns to focus on your subject result in frustration, for example, when you finally focus on the branch where that fast-moving warbler had been a couple of seconds ago! Make sure the close-focus distance is acceptable, ideally down to between two and three metres. the wheel sufficiently ribbed and deep enough to allow positive finger-contact for operation, even when wearing gloves? Check the dioptre also allows for single eye fine focus adjustments to be made and that it will not slip from its setting; some models feature a locking mechanism in this area. Is it centrally mounted or built into one of the eyepieces? You will not need to operate with any frequency but you may have preference.

Magnification: this is a matter of personal preference and it can have an impact on some aspects of image quality, such as brightness, depth of field and field of view.The majority of birders select either 8x or 10x, but 7x is also widely chosen. Generally, for the same size of objective lens, the higher the magnification, the darker the image, shallower the depth of field and the narrower the field of view. All these factors vary considerably between different manufacturers, though, with models from top-flight manufacturers frequently out-performing lower-budget 8x binoculars in these areas. Comparing models of the same magnification from different manufacturers will serve to illustrate this.

Image: many binoculars are sold on image quality alone, but a fantastic image is of little value in a binocular which feels uncomfortable or is difficult to operate. Assuming you have found some models you are physically comfortable with, try some simple comparison testing. Check first for chromatic aberration (colour fringing), which appears as a bluish margin along one side and a yellowish margin along the opposite side of a dark object when viewed against a light background. A bare tree branch against a cloudy sky makes an ideal subject for this test. All binoculars show colour fringing, ranging from being virtually absent in topend models to being annoyingly evident in some ëbudget binsí. Decide what degree you are prepared to live with.

Check to see if the image is sharp from one edge of the field to the other and if it remains in focus across the entire field; do straight objects appear to curve unacceptably at the edges? Measure the image colours against reality: are they true-to-life? Most binoculars have a colour cast, which can lend the image either a cold blue or a warmer yellow tone. It is normal but it should be very subtle in either case, although in some models it can be overbearing. Look at the field of view ñ the width of field visible in metres at 1,000 metres range.This varies considerably between models ñ some with a narrow field can almost give an impression of claustrophobia ñ but generally the higher the magnification, the narrower the field of view. Choose a model with a wide field if you are going to be seawatching or spending a lot of time birding in open country. Finally, check the depth of field.

Do you have to constantly refocus the binoculars to observe birds which are not separated by any appreciable distance, for instance?

Durability: a binocular is likely to be an expensive investment so prevention waterproofing: is it gasfilled and therefore sealed against liquids and dust? Most binoculars now sport rubber armour as standard. How tough is the rubber? Some types of rubber can be surprisingly sticky, attracting fluff, dust and so on, so check that this will not be a potential source of annoyance.

One thing is for certain: manufacturers cannot afford to stand still, and many now have a better understanding of the needs and requirements of birders and some are now actively using them as consultants in the design process for new models.

In binocular design terms, anything is possible but everything comes at a price and many ideas which are initially pursued never make it to the shelves as finished product because they are not commercially viable. It will be interesting to see the innovations which emerge over the next few years.Watch this space!

buying tips

Before you buy, prepare a shortlist of models to test, based on your experience with binoculars you like and can use to benchmark potential purchases. The detailed tables following this review (see pages 32-34) will enable you to make initial comparisons in price and specification between shortlisted models prior to your first trip to your local dealer. And finally, remember the following advice:

• Forewarned is forearmed, so glean as much information as possible about the binoculars you have shortlisted from manufacturersí websites and sales literature, and from the individual indepth reviews published in Birdwatch and other publications.* Aim to test all binoculars at a supplier which has facilities as close as possible to field conditions, or at a retailer which stages field-day events at nature reserves around the country (see page 10 for events in July).
• Compare different models on a cloudy day or in poor light conditions: you will find that the differences in performance between good and poor quality binoculars are more evident under these conditions.* Check the terms of the warranty and the guarantee period, and ensure that the model purchased comes with documentation confirming it is from an approved UK importer: so-called ëgreyí imports can prove problematic if they need to be returned for repair.
• Look out for special deals on models which have been superceded or discontinued.* Manufacture your own bargain, haggle over price, ask for a cash discount and look out for ëextrasí or any package deals on offer which may help justify parting with your cash.
• nternet sales of optics have increased considerably in recent years. If you are 100 per cent certain of the binocular you want to purchase then buying on the internet, or through mail order, could be a risk worth taking. You can potentially save a considerable sum of money on a top-of-the-range model if you buy in this way, which is less likely to be flawed than one from the bottom end of the price range.

About this guide

These tables feature ëmainstreamí birding binoculars ñ those widely available models with 7-10x magnification and objective lenses between 30-50 mm. ëMarginalí models such as digital binoculars and compacts are not included. Key to tables:

• Price: recommended retail price.Weight: in grams.
• Size: length x width in millimetres.Field: field of view in metres at 1,000 metres.
• Focus: close focus in metres.¶ Waterproof: yes (usually gas-filled), no, or ëweatherproofí.Prism type: roof or porro prisms.
• Guarantee: guarantee or warranty in years.  Then insert charts from pages 32-34 

Boxout 1

Opticron has one of the largest model ranges of any manufacturer, offering a huge array of porro- and roof-prism models. This is the DBA 8x42.

Boxout 2

What the birder never sees: a crosssection of the Leica Duovid 8-12x42 reveals the complex inner workings of a binocular.

Boxout 3

Magnification is very much is a matter of personal preference. Manufacturers often give a choice of 7x, 8x or 10x. This is the 7x42 from the Zeiss Victory range.