Binoculars and Telescopes for Birdwatching
No real birdwatcher will be without a pair of binoculars. These are usually essential for the proper identification of a bird and will help considerably in the observation of close detail such as feeding methods and habits.
There are enormous numbers of binoculars on the market and choosing a pair which is going to suit your needs and pocket needs careful thought.
The points that guide you in your choice of binoculars are the magnification, the field of view, the optical quality of the lenses, weight, size and finally, no doubt, cost; you should have all these points in mind when choosing. For general birdwatching, which means that one day you may be watching in a wood and the next by an estuary, binoculars which magnify 8 x , 9 x and 10 x are the best. Below this the magnification of the image is so small as to be nearly worthless, and with higher magnification you will not only be magnifying the image of the bird but also the shakiness of your hands and the effect of the wind buffeting your binoculars. Some people can manage to hold 12 x binoculars but once you get above this magnification you really need to be able to fix your binoculars to a tripod or some firm base.
The second point to be considered is the field of view which is linked to the amount of light gathered by the objective lens of the binoculars. The wider the objective lens the better the light-gathering power and the better you will be able to see in poor light. Generally, the most commonly used binoculars for birdwatching have objective lenses with a diameter of somewhere between 30-50 millimetres. The number of times that a pair of binoculars magnifies and the diameter of the objective lens produce the figures which are found on glasses (e.g. 8 x 30, 9 x 40, 10 x 50) and from these figures it is possible to gain some idea of the suitability of the glasses for use in poor light. If you divide the magnification into the figure for the width of the objective lens, the higher the answer you obtain the more suitable the binoculars are for use in poor light. In fact, the result should be higher than four for hand-held binoculars. Lenses which have been coated with a non-reflecting material, or which are said to be ‘bloomed’, usually have superior light-transmitting properties so a figure as low as four is passable with these lenses.
Generally speaking, the field of view decreases with increasing magnification but increases with the diameter of the objective lens. A wide field of vision is particularly helpful when you are trying to watch and follow a bird in dense cover, for instance in a woodland. The field of view for 8 x 30 binoculars is normally 120 metres at 1000 metres.
The optical quality of a pair of binoculars is very difficult to assess when buying for the first time. This is really where the help of an experienced person is necessary. You need the best resolution of detail over all the field of view. With cheaper glasses the resolution may fall away at the edges, and on some glasses you can see colour fringes where the image is surrounded by a faint colour halo; these should be avoided.
When choosing binoculars a compromise may be necessary between high magnification and field of view. This drawing shows how the field of view decreases with magnification.
Finally, do not get binoculars which are too big to hold in your hands or which feel heavy when you are handling them in the shop, because they will feel even heavier on your neck after an hour or so of bird watching, and your hands and arms will soon tire trying to hold them steady in front of your eyes.
Generally speaking the more money you can afford to pay the better the chances are that you will get a pair of binoculars which have a good lens system and reliable mechanics which should last you a lifetime. However, it is possible to buy reliable and relatively inexpensive Japanese binoculars.
Some binoculars are equipped with zoom lenses which enable you to find a bird at low magnification and, when you have located it, boost the magnification to obtain a better view. These are, I think, of dubious merit as there is another mechanical piece to go wrong; they add weight and. Possibly, also delay in obtaining a good view of a bird which may only be perched momentarily.
While binoculars are almost essential to birdwatching. Telescopes become useful, if not essential, when you become really interested and need a high magnification to identify or watch birds at long distances, for example, on estuaries and at sea.
Remarkable changes have taken place in the design of telescopes in recent years. Twenty or more years ago most telescopes consisted of a system of lenses housed in a series of tubes which could be slipped inside each other when being carried or extended when being used. Modern design has eliminated the need for great length and, except for prismatic telescopes, there is only one exterior tube, focusing being achieved by a milled knob, while another knob is adjusted to increase the magnification. Prismatic telescopes, however, are of a fixed length and focus is usually achieved by a small milled knob. Some prismatic telescopes also have ‘zoom’ eye-pieces which means that, once you have found the target bird, you can twist that part of the eye-piece and increase the magnification.
The magnification provided by a telescope usually ranges from about 20 x to 60 x. However, as the magnification increases the amount of light being transmitted through the lens is reduced, unless the diameter of the abject glass is also increased enormously. I have a zoom-lens telescope but I 5nd that I tend to use the lowest magnification – 25 x – in this country. Even in parts of the world where the sun is brighter I rarely use a magnification above 40 x. The resolution of detail with the prismatic telescope seems much finer than with the tube type.
Greater magnification, as in binoculars, increases the problems caused by hand-shake and a firm but light tripod with a pan and tilt head is absolutely essential to hold the telescope steady. Incidentally, it should ideally be a black one so that light is not reflected back to the bird you are trying to watch.
The difference between the British and American birdwatcher becomes very apparent when one comes to the use of telescopes. The American ‘birders’ seem to carry telescopes everywhere, and use them regularly, whereas the British are far less regular in their use of ‘scopes. Tripods and telescopes are perhaps less liked because they are more clutter. I recently had a simple sling for my telescope made by a local saddler, it consists of a webbed belt about 2 or 3 centimetres wide and about 150 centimetres long. Two straps of about 15 centimetres in length are fixed to the webbing about So centimetres apart – this distance depends on the length of the tripod when in a closed position. The top strap remains strapped round the tripod beneath the pan and tilt head and the second strap clasps the bottom of the legs when the whole tripod is collapsed. The whole lot is easily carried over your shoulders. You have only to undo the bottom strap, deploy the legs and your telescope is ready for action.
Prismatic telescopes are more expensive than the tube telescopes but I think that their better resolution of detail makes them well worth the extra cost. I have used prismatic telescopes for many years. and although I have peered through tube telescopes since then from time to time I have never been urged to change over to them. Most ornithological magazines carry advertisements by optical dealers, but, perhaps it is best to find a satisfied customer who can recommend a dealer or go to one who gives you the opportunity to try his range of binoculars and telescopes in the field.