Binoculars for hunting, nature viewing and leisure time purposes
No hunter can do without good binoculars. Which criteria determine the price of the optical device? Is it the brand name which makes the binoculars expensive? And does good quality have to be expensive?
- Hunting binoculars - the basics
- Key performance indicators for binoculars
- Exit pupil
- Comparison by twilight factor
- Quality optical coating
- Buying criteria - summary
Hunting binoculars - the basics
Binoculars are based on an optical principle which allows rays of light to reach the eye via a siystem of prisms and lenses. With each change of the medium, e.g. from air to glass or from glass to air, a small percentage of light intesity is lost. You can try out this effect without binoculars. Look outside through a window pane and then open the window. Do you notice that the view is brighter when you do not look through a pane? With binoculars or scopes the same physical principle applies. However, the extent of the loss of light can be limited by a special coating.
Binoculars are complex optical instruments. Their main goal is to provide a clear image to the eye of the viewer, however all binoculars are a trade-off between different qualities. Usability and optical performance are two factors that are contrary to each other. Therefore carefully think about the intended areas of use before you buy new binoculars.
Other purchasing criteria are waterproofness, nitrogen filling, lotus effect and the general haptics of the binoculars. Additional features such as range finding capabilities or ballistic information extend the optical basic functions. Wearers of spectacles will find the foldable eyepieces useful which can be adjusted to their respective eyesight.
Key performance indicators for binoculars
High light transmittance depends upon the lense diameter of the binoculars. Lenses are oriented towards the object of observation, hence the name. The following rule of thumb applies: the more ingress of light there is, the more light can reach the eye. . As a rule night-time binoculars have a wider lense diameter than binoculars intended for stalking. Of course, there is a limit to the diameter of lenses, as binoculars must still be practical to handle. Dimensions and weight are the natural delimiters of binoculars. Seen the other way round, this is also why there is a certain limit to the performance of handy pocket binoculars..
Oculars are lenses which are oriented towards the eye. Their baisc function is a magnifying effect. A high magnification factor. makes distanced objects appear to be near. Again, there are practical limits to high magnification. If magnification is extremely high you won't be able to freehandedly hold the binoculars.Besides, high magnification is attained at the cost of a small percentage of light intensity. For hunting purposes a magnification of 8x up to 10x is practicable. For higher factors of magnification (needed of bird watching or nature observation) it is advisable to use a tripod as is common with scopes. The chief parameters of binoculars are expressed in perfomance indicators such as 8 x 56 or 10 x 42. The first number denotes the magnifying factor, the second number stands of the lense diameter.
A high magnification diminishes the field ov vision. Fields of vision above 130 m can no longer be perceived by the human eye. If this parameter is noted as an angle value, 1° corresponds to 17,5 m.
It is tempting to think that with extremely wide lense diameters a correspondingly high light intensity could be achieved. However, this is not the case. Here, the limiting factor is called exit puil. The exit pupil is calculated in milimeters and obtains by the following division: Exit pupil = lense diameter/magnification. Example: 56/8 = 7 mm exit pupil for hunting binoculars 8 x 56. Lenses with such values are part of the assortment by Leica, Zeiss, Swarovski, Steiner or Minox. The vaulue of the exit pupil denotes the diameter of the light beam which exits the binocular to hit the eye. In darkness the human eye pupil can open up to 7 mm, with age this value diminishes. An exit pupil above 7 mm will therefore not improve the perceived light intensity.
The three factors above are interdependent upon each other. In general an increase in the optics' performance is tantamount to an increase in the optics' weight. Therefore, in good weather conditions and with good light hikers do not really need a 8 x 56 for their trek.
Comparison by twilight factor
Many customers inquire about the twilight factor: this is a purely calculated value. It denotes the sqare root obtained from the multiplaction of magnification and lense diameter. Examples: binolculars A (10x44) as well as binoculars B (8 x 54) have a twilight factor nearing 21. The exit pupil of „A“ is only 4,4 mm, that of „B“ is 6,75 mm. Although the twilight factor is similar binoculars B is better suited for twilight use on the strenght of its higher light transmission. The twilight factor does not circumscribe the optical quality of binoculars! Low cost binoculars made in Asia may have the same twilight factor as high quality premium range binoculars. Still the optical quality comes short defined as it is by the type of lense and its coating. The overall make does not compare.. Therefore by itself the twilight factor has little to say on the quality of particular lenses. Nor is the lense colour a quality criterion.
If water gets into the optics or if lenses get moist no reasonable viewing is possible. For this reason hunters tend ot rely on quality. Apart from the optical performance values it is the design, the haptics and finally the usability which form importan purchasing criteria for high-end optics.
Quality optical coating
High quality binoculars by Zeiss, Swarovski and Leica have multiple-coated lenses and prisms. Both the coating and the particular type of glass make for a high light transmittance. As regards light transmittance, the best binoculars achieve values of 92% and above. Type and extent of coating will significantly determine the price. In difficult twilight light conditions you will notice the difference. High quality binoculars will show a crystal clear image even at the edge, lower quality optics will distort the image or make it appear blurred. Colour accuracy also plays a significant role for good hunting binocular or for binoculars primarily used for nature observation.
Buying criteria - summary
- Intended use
- Lense diameter
- Water and pressure resistance
- Design and haptics
- Brand and price
- Suitability for wearers of specs
- Accessories and special functions
Take your time when you select binoculars. High quality optics have their price, but this will be a long-time investment giving you plenty of return particularly when you are hunting.