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Magnification: The most common magnification sizes used by birders are between 7X and 10X. 10X is generally regarded as the largest magnification which is practical for hand held binoculars, although image stabilising technology may soon change this. 7X may seem to a bit weak, but is easy to use, and combined with a large objective lens, provides good performance in low light conditions. 8X or 9X is most popular among birders, although many birders seem to like the power of 10X.
Size of Objective Lenses. The objective or "light gathering" lenses are important as they determine the amount of light that is received by the binoculars. 7X32 means that the objective lens is 32mm in diameter. The amount of light the binocular receives is a function of the area of the lens rather than diameter. This means that 7X50 objectives gathers more than twice as much light as 7X35 lenses. The size of the objective lense affects both image resolution and performance in poor light conditions. All things being equal a 10X50 will provide better resolution than a 10 X40.
Field of view. The wider the field of view, the easier it is to scan the terrain, and to pick up the bird, or hold a moving bird in your field of vision. I use a 7X42 Wide Angle and personally enjoy the very good 8.2 degree field of view that these offer.
Depth of field. The depth of field describes how much of the field is "in focus" at any one time. Binos with a poor depth of field require a great deal of attention to focussing in order to keep things in sharp focus. Naturally it is also a lot harder to pick up a bird, that you have not yet focussed on, if the depth of field is poor. Binos with a good depth of field make for easy birding and less concern to focus all the time.
Eye Relief. Eye relief is particularly important if you use spectacles, and describes the minimum distance between the exit lens and your eye. A long eye relief means that you can hold the binoculars further from the eye (with spectactles in between) and still get the full benefit of the binoculars. A good eye relief figure is from 16mm upwards.
Size of exit pupil. The exit pupil size is the size of the pupil through which the light reaches your eye. In good light a 4mm exit pupil produces the same brightness as a larger exit pupil, this however changes in dim light, where the larger exit pupil provides a real advantage. A less obvious advantage of a slightly larger exit pupil is the ease of use. A small exit pupil requires precise alignment with your eye, and tends to be more strenuous to use, particularly if you are birding for long periods. A larger exit pupil is more relaxing to use.
Close Focus. The capacity to focus on those warblers that come within four or five metres is a vital factor for good birding binoculars. Obviously the closer the better, but a close focus of 10 feet is desirable if you are short-sighted ! For Southern African bush birding I would not recommend binos that have a close focus of greater than 16 feet.
Weather-proofing. Weather proofing varies from "full weather proofing" to shower proofing to no weather proofing at all. Of course fully nitrogen-purged and sealed binoculars are ideal, but come with a hefty price tag. For South African conditions full weather proofing is not generally necessary, and many of the better quality mid-range binoculars provide adequate shower proofing. This does of course mean that care must be taken in rainy conditions, and that the binoculars may have to be nursed in very wet conditions by storing them with a silicon dessicant. If you are going to be birding in rainy conditions make sure you get a pair with a rain guard for the front lenses.
Type of lenses and lens coatings. Special coatings on the various lenses found in binoculars are aimed at reducing reflection, and it is here that the greatest advances in image quality have been made. Cheaper binoculars usually have coatings only on the external lenses, while better binos have coatings on all lenses. Single coatings on a lense reduce light loss to 1.5 % from about 4% for uncoated lenses. The best multicoatings achieve a figure of less than 0.5% per lens. Considering that a pair of binoculars typically has more than 10 lense surfaces the difference between "fully multicoated" and "coated" can be quite substantial ! With advances in technology, some binoculars in the R1500-2000 range are now fully multicoated, while formerly only the very best brands had this feature. I would recommend fully multicoated lenses for birding binoculars. Look for the label "fully multicoated" and "BAK-4 prisms" to indicate quality coating.
Key Choices : Magnification, Style and Price
1. Binocular Magnification: choosing between a 10X or an 8X
This is one of the most common choices that binocular buyers have to make. Obviously one should get a better, more magnified view with a 10 power binoculars. In reality, the larger magnification is more difficult to handle, and it is doubtful whether even experienced birders actually see more through the more powerful pair. I used a 10X50 Bushnell before switching to an 8X42 Meade Safari Pro and can honestly say that the 8X42 are easier to use, and provide a better quality image.
The key issue is quality and the diameter of the objective lenses. All things being equal, a 10X50 will provide better image sharpness then a 10X40, as it gathers more light. A top of the range 8X32 will provide a better, clearer image than most 10X binoculars will, quite apart from the ease of use and the stability of the image you are seeing.
8X32 and 10X40 have about the same magnification to objective lense ratio and are generally regarded as the standard, or minimum for birding, where one generally needs good light gathering ability. Nevertherless a 10X50 or 8X42 will, all things being equal, provide a better image, and are popular among birders willing to carry the extra weight. In addition these binoculars may also offer a wider field of view, which some birder regard as important, as it allows one to pick a bird up more easily.
I personally prefer a slightly larger objective, as it provides for more resolution and better image in poor light conditions, and do not mind the slightly extra weight. My favoured specs are 10X50 and 8X42, witht the larger pair getting the nod if one is birding over larger distances : such as at Barberspan. For normal bush birding the 8X42 are ideal, particularly if they have a good wide, field of view.
Porro vs Roof Prism. There was a time, when roof prisms were regarded as the best. Zeiss, Leica and Swarovski made the roof prism famous by producing the best high quality binoculars in this format. The weight advantage, compact and durable design and the elegant shape of roof prisms has contributed to making them almost universal among top birders. In fact the roof prism design is not as good optically as a porro prism design of the same specifications. In practise this means that you can get the same quality view at a lower price by going with porro prisms. Since many manufacturers have produced their best (optically) binoculars in porro prism format, there is now a move back to these binoculars, although there is a compromise in weight and bulk and invariably build quality as well. Manufacturers such as Bushnell, Nikon, Meade, Swift and Celestron have all produced excellent Porro Prism binoculars which offer excellent optical quality at a fraction of the price of the top roof prisms from Swarovski, Zeiss, Leica and Bausch and Lomb.
The key choice: How much is worth paying ?
A couple of years ago, there was a big difference between the top-of-the-range binos and the average "good" binoculars. In the last decade binocular manufacturers have become more aware of the needs of birders and far more "bird-worthy" binoculars exist. Full multi-coating is now common on binoculars in the $ 200 range, as is the combination between large objective lenses, good depth of field and a relatively wide angle. This means that there is not all that much to seperate a good $200 birding binocular from the top of the range $1000 models. What usually does seperate the pairs is a marginal optical difference, water-proofing and rugged "built-to-last" quality , as well as the more compact roof prism design. Given that most birders simply cannot afford $1000 binoculars I would recommend that one buys in the $170=$300 range and gets the feel of what you personally prefer before shelling out R9000-00 !
Good birding binoculars - a selection of mid-range pairs
Based on my internet research and talking to birders, there are a number of "mid-range" priced binoculars which are excellent for birding purposes. Prices are given in US Dollars for comparison, as prices for many makes were not available in South Africa, or are often wildly inflated ! PRICES are A ROUGH guide only as they can vary a great deal depending on where and how you buy them !!
Expensive (but not that expensive !)
Swarovski 8X30 SLC Mark III
$ 650 +
Bausch & Lomb 8 X42 Elite
$ 650 +
Nikon Superior 10X42 ES $
600 + (rated by some as the very best !)
Swift Audubon 8.5X44ED $
450 (ED glass)
Swift Audubon 8.5X44 Roof Prism
($420)
Celestron Regal 10X50
$450 Roof Prism/Waterproof)
Eagle Ranger 10X50 $ 450
(Roof Prism/Waterproof)
Celestron 9.5X44 ED
$ 350 (ED Glass)
Bargain Value - still excellent Binoculars
Nikon E 8X30 (Criterion Series)
($300)
Baush & Lomb 10X40 $300
(about R4000 in SA ?)
Bausch & Lomb 8X36 Custom $250
Swift Audubon 8.5X44 (standard)
$250
Swift Audubon Kestrel 10X50
$ 230
Celestron Ultima 8X40 (WildBirds
Unlimited) $230
Celestron Ultima 10X42WA $220
Meade Safari Pro 10X50 $190
Swift Ultralite 8X32 & 8 X42
$ 180
Meade Safari Pro 8X42WA $
180 *** My personal recommendation
Leupold WindRiver 8X42 Porroprism
($170)
Swift 8X40 Plover ($100)
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