Terms & Conds
Choosing your binoculars
Choosing your binoculars
Choosing your binoculars
Example: 8x42. The first figure '8' denotes the magnifying power and allows the user to see an object 1/8th the distance away. The second figure '42' represents the diameter of the objective lens (the large end) in mm through which light enters the binocular. The symbols or letters that often follow provide important
information as to which binocular may best suit your requirements.
The letters Z usually denotes conventional porro prism binocular body styles, which gather light from lenses further apart than one's pupils giving a stereoscopic effect that counters the foreshortening of perspective caused by magnification. The letter D stands for roof prism binoculars, which although more compact than porro
prism models, tend to be more expensive and for the same price often under perform their larger counterparts.
The suffix B when used on roof prism binoculars including Opticron BGA models mean the eyepieces have a long eye relief giving full field of view for spectacle wearers. GA stands for rubber armouring and W or WA denotes binoculars that give wide-field or wide-angle vision.
Centre focusing 'CF' is generally more popular than individual eyepiece focusing 'IF' especially when readjustment is required at less than infinity settings. Most 'IF' binoculars are 7x magnification which give a large depth of field thus negating the need for focusing adjustment at distances over 100m.W
For hand held use, practical trials suggest choosing a binocular with a magnification no greater than 8x or 10x, the reasons for which are as follows. The magnification effectively spreads the available light over the image being viewed. The higher the magnification, the larger the image being covered and
hence the lower the relative brightness of the image. Higher magnification binoculars also give a reduced depth of field (distance in clear focus at one time) and field of view. Lastly, the higher the magnification the more natural hand-shake or tremor affects the stability of the image. If you want binoculars over 10x magnification it is
advisable to try them first and consider using a support such as a tripod to attain a stable image, especially when viewing for long periods.
The objective (OG) lens and light transmission For any given specification of binocular the amount of light passing through the instrument (known as light transmission) varies according to the optical design, optical quality and lens coatings used. However, a few general rules can help you in your choice. The amount of light
entering the binocular is directly related to the surface area of the OG lens. A 50mm OG will admit 2.5x the light of a 30mm OG. The amount of light reaching the eye when positioned at the eyepoint of the binocular is known as the exit pupil diameter or EPD. Its size can be found by dividing the OG diameter by the magnification, e.g.
the EPD of an 8x32 = 4mm, the EPD of an 8x56 = 7mm. As a general rule the iris in the eye dilates between 2 and 3 mm (bright sunlight) and 7 and 8 mm (twilight) and therefore a choice should be made on the type of use the binocular is being put to. For general use an 8x40 with EPD of 5mm is recommended.
FIELD OF VIEW
The field of view of a binocular is expressed as either the width of panoramic view in metres from a distance of 1000m or in degrees. For example: 1 degree = 17.45m approx. A binocular is usually stated to be a wide-angle instrument if the angular field in degrees when multiplied by the magnification gives a figure
equal or larger to 65. The field of view of a binocular is dependent on the overall design and for any given design directly related to the magnification. As you read through the information and compare models in the same range, you may find that on occasions the 10x magnification model gives a similar, equivalent or larger field of
view as the 8x magnification model. This is because different eyepiece designs are used within a range.
When choosing your binocular bear in mind the weight and size as you may be carrying them around all day.
Although a pair of compact pocket sized binoculars will not perform as good as a full sized pair,it is sometimes disirable to have a smaller pair to carry around as a larger pair may just be left at home!
A NOTE ABOUT COST!
It does not always follow that the more that you pay the better the instrument will be for you!
Indeed, the quality goes up the more that you pay (provided they are bought from a reputable supplier who knows the models and brands to avoid that are overpriced)
Generally if you double the cost, the quality is not double but there are a number of qualities that may increase by a certain percentage. EG: Edge to edge distortion, colour fringing, close focus and build quality.
USING YOUR BINOCULAR
To adjust to the spacing of your eyes known as inter pupillary distance (IPD), simply rotate the two sides of the binocular around the centre hinge until a single rounded picture is obtained when looking through both eyepieces. Some roof prism binoculars have two hinges and a single rounded picture
is obtained by rotating both hinges simultaneously around the centre focusing plate. As mentioned, most binoculars are focused by turning the centre focusing wheel. If however there is a difference in strength between the eyes, the dioptre scale (usually located on the right hand eyepiece) can be adjusted in order to
compensate. To set the binoculars for your eyes, focus with your left eye on an object using the focusing wheel. When the object is in sharp focus, close your left eye and open your right adjusting the dioptre ring until the image being viewed becomes sharp. Opening both eyes should then reveal the sharpest picture at all distances.
Wearing glasses Many binoculars provide the full field of view when wearing glasses by either folding down rubber eyecups or by turning/pushing retractable eyecup assemblies to the 'down' position. As a general rule the longer the eyerelief - the distance between the surface of the eyepiece and the point where the pupil is positioned for full field of view - the better the instrument for spectacle wearers.
Roof Prism Binoculars
Popular with Birdwatchers and a bit more compact and usually lighter in weight than their Porro prism or ZCF Counterparts. Many Roof prism models are waterproof and are better sealed against the elements as most of the moving parts are internal. A good choice for Holidays,Birdwatching and Safari but great for most uses. The interpupilary distance or width of eyepiece spacing is normally smaller than Porro prism Binoculars, making them more suitable for those with a narrower eye spacing. Because the objective lenses are closer together, the image is slightly flatter with less depth of focus than the Porro prism Binocular. This is not a problem and you would not notice unless you compared the two models side by side.
Porro Prism or ZCF Binoculars
A little bulkier than roof prism models but many people find them more comfortable to hold as the shape gives a nice grip that encourages a steady braced stance almost like a tripod with the arms.
These type of binoculars give a slightly more stereo image with a little more depth of focus. ie; slightly more perception of depth in the image.Also many Porro prism binoculars will give a slightly better brightness.
The Porro prism or ZCF Binocular is a good choice for the Astronomer.
Compact or pocket sized Binoculars are convenient for holidays and walking activities as they are small and easily stow away when not being used. They do not collect as much brightness as a full sized pair of Binoculars but this will only impact in very low light conditions and will give just as good image quality,brightness and colour rendition as a latrger pair when light levels are reasonably good. Lens technology over the past few years has got better and Compact Binoculars are much better than the earlier models. Well worth considering a compact pair if weight and size is a major consideration.
Observation Binoculars or Large Binoculars
These are Great for long distance viewing and for Astronomy. The larger objective lenses gather a lot of light and they come in a range of magnifications, Some have interchangeable eyepieces which make for more versatility.
These observation binoculars will need to be mounted on a sturdy tripod for best use with only up to around 80mm models which can be used with limited hand held situations. eg; aircraft spotting.
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Choosing your binoculars