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Choosing Binoculars :: Learn A-Z Digital :: Choosing the right Digital Camera :: Choosing the right Filters
Choosing Binoculars
Choosing the right binocular can be difficult, as it is a very personal choice and only you can decide between performance and price. Ultimately, you should feel comfortable using your chosen binocular and should not be overly concerned with styling and features. The following pages explain the various aspects to consider when purchasing either a binocular or telescope and if you need further help, then go to one of the many optics field days held at most of the RSPB reserves all year round.
What do the figures mean?
All binoculars have a set of two figures indicating their specification (for instance 10x40). The first figure refers to the magnification. This is typically between 7x and 10x, although specialized binoculars range higher and lower than these. The second figure describes the diameter of the large lens (called the objective) in millimetres. Generally speaking, the larger this lens is, the greater the amount of light that will be gathered and therefore, the brighter the image.
What magnification do I need?
Higher magnification can cause:
difficulty in holding the binocular steady.
reduction of field of view.
loss of image brightness.
A higher magnification would generally be recommended for use in hides or for viewing at estuaries and reservoirs.
Lower magnification can provide:
closer focusing.
greater field of view, improving use.
greater depth of field.
These lower magnifications are ideal if you are also using a telescope. For general use, lower magnification binoculars are recommended as they tend to give a brighter image with more depth of field. If you do not intend to use a telescope, a higher powered 10x binocular is a good compromise.
Types of binocular
There are two main designs of binocular:
Porroprism: traditional, classic shape and design.
Roof-prism: recognized by its straight tube like appearance.
It is also worth considering a miniature binocular if size and weight are important factors, although this type does not offer such good light-gathering power or field of view as full-sized binoculars.
Features
Internal focusing: when focusing, lenses are moved in and out to increase or decrease their distance from the internal prisms.
With many binoculars you can see the eyepieces, connected by the bridge moving up and down. As the description suggests, internal focusing incorporates all these moving parts inside the unit.
Rubber covering: This does not make binoculars water-resistant or dust proof. However, it does offer better protection against knocks. The letters GA (German word Gummiarmierung) sometimes included after the specification, denotes that the binocular is rubber armoured.
Bak-4 prisms: These are larger than the alternative Bk-7 versions and reflect more light.
Eye cups:
Most binoculars now are designed to be suitable for both spectacle and non spectacle wearers (sometimes denoted by a ‘B’ after the specification). In order to achieve a full field of view for spectacle wearers, the eyecups are retracted - either rubber fold down or push / screw down types so that the actual distance between the eye and the binocular lens remains constant.
Waterproof binoculars: Now widely available, these instruments will almost certainly be nitrogen filled to eliminate internal fogging.
How much should I pay?
Porroprism binoculars are less expensive to construct than roof-prisms, and will usually be optically superior when compared with roof prism models at similar price levels. This highlights the necessity to pay more money for roof-prism designs of comparable image quality. As a general rule, low price roof-prism models will not provide the same performance as equivalently priced porro designs.
Conclusions
For general Birdwatching, the lower magnifications tend to be better (8x30 or 8x40). If you intend to use a binocular in low light such as dawn or dusk and in woodland, consider a 7x42. The best compromise for hide use would be the higher powered instruments with adequate objective lens diameter (10x40 or 10x42).
Telescopes Explained
Telescopes have become increasingly popular among birdwatchers. By offering higher magnification, they add a new dimension to bird watching. Telescopes come in component form - the body, eyepiece and appropriate support, usually a tripod. It is important to take care when choosing your equipment.
What magnification do I need?
Telescope magnification range from 15x to 60x. Some specialist instruments offer even higher power. If the telescope has a fixed eyepiece, 20x or 30x is normal. Most telescopes on the market today have a range of interchangeable eyepieces, so you can choose more than one. Wide-angled eyepieces of 20x to 30x are good for general use; a 40x might be useful for longer distance work.
When using higher magnification, the image brightness and field of view decrease dramatically. Any shake from the support becomes more evident. In practice, this means that the higher power eyepieces are best used in bright conditions for stationary birds.
Zoom eyepieces work well with some telescopes, usually the ones with the larger objective lens. The range is usually between 15x & 60x. But remember, with higher power, the amount of light passing
through to the eye will be reduced.
Smaller telescopes have a 50 or 60 mm objective lenses, and being compact, they are ideal for general work. Most manufacturers offer telescopes with larger objective lenses, between 65mm and 85 mm. These perform better in low light, but the large lens adds to the size and weight of the instrument. Because of the increased light transmission, zoom eyepieces work better with this type of telescope.
Basic guidelines
For general observation, choose a compact 60mm scope with a wide angled 20x or 22x eyepiece. If you need higher power, choose a 30x or 40x eyepiece in addition to, but not instead of the general one. The larger 65 mm - 85 mm telescopes are ideal for use in low light or from a fixed position such as a hide. Again the wide-angled, fixed 20x - 30x eyepieces are best, but a zoom works well with this type of telescope. If you wear spectacles, choose an eyepiece which has a click-down rubber eye cup, although you will still lose some field of view.
Straight or angled?
Most telescopes come in either straight or angled form. On the straight type, the eyepiece follows the light path from the objective lens. On the angled type, the eyepiece is at 45º to the scopes body. Both designs have their advantages.
Straight
Easier to use and find what you are looking for
Can be cheaper than angled models
Better to use when sitting down in hides.
Angled
Easier to follow moving birds
Easier to watch birds in treetops
Tripod does not have to be erected so high and is therefore more stable.
More suitable for tall people.
Also suitable for astronomy.
How much should I pay?
The starting point for a good 60 mm telescope with a fixed eyepiece is £250: add £100 - 150 for a zoom eyepiece. From £250 to £500 you will find better telescopes and this is the starting price for the instruments with larger objective lenses.
Over £500 buys you a telescope of the highest quality. Some top of the range instruments at around £800 - £1000 have low-dispersion or fluorite glass; giving a brighter and sharper image. Some telescopes are waterproof but it is worth getting a case or a model with rubber protection. Stay-on-cases are a good idea and are available to fit most models.
Photography through a telescope
In most cases it is possible to connect a camera to a telescope via an adaptor, but it is worth remembering that a telescope is designed to look through, not for taking pictures, and the results will not be as good as a dedicated camera lens.
Care and Use
Looking after binoculars & telescopes. Binoculars are valuable tools, so it is worth taking a little advice to learn how to achieve the best results and keep your binocular in good working order. Some models may represent a considerable financial investment. With the correct care you might well expect it to last a lifetime and with the good advice you can maximize it’s performance.
The basics After using a binocular in the rain, always wipe it dry. If moisture is apparent on the internal optic surfaces, leave it in a warm place to dry. Never dismantle it and do not put it back in the case until it is fully dry. Treat a telescope in the same way.
If your telescope has interchangeable eyepieces, change them as little as possible, every time you remove the eyepiece, dust will get into the telescope.
Problems?
When a binocular is manufactured, the optics are very carefully aligned using special equipment, so that you see only one image.
The most common problem experienced is misalignment of the optics and the consequent double image, as a result of the instrument being knocked or dropped. This can be rectified but only by specialist repairers with similar equipment to that used by the manufacturer. Some people may not notice slight alignment faults, so it is best to get someone else to check your binocular at regular intervals..
How to use your binocular
When you first look through a binocular you should:
Adjust it for the width between your eyes.
Adjust the individual eyepiece for your eyesight.
Note the settings.
How to use your telescope
A telescope is never a substitute for a binocular and it takes time to learn to use one - but it is worth the effort!
The following points should help you:
Try to use a tripod or support whenever possible.
Learn to keep both eyes open. If the light is bright use your hand as a shade.
Do not breath on the eyepiece, especially in cold weather, as this will cause the lens to fog up.
Using a telescope and tripod
It is a good idea to carry your telescope ready mounted on a tripod so that it is easy to use quickly. A strap can be useful, although many birders carry their telescope and tripod on their shoulder, making it easy to use when needed. A tripod with a quick-release plate will be useful in hides. If your tripod does not have this, it is possible to fit one as an accessory.
When you are out in the rain and not using your telescope, keep the lens cap on. For extra protection a `stay on case’ is a good idea. Once fitted these should be regarded as a permanent part of your telescope.
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