Binoculars: simply the best way to improve your experience of watching birds in the garden and beyond.
Binocular Specification and Terminology
01 | Magnification.
The binocular magnification specification is the first number in the binocular description. e.g 10 x 42 binocular has a magnification power of 10 times. That is to say, the viewed image will be 10 times larger than with the naked eye.
While a higher magnification will make the image larger and easier to view it will also reduce the field of view and make any movement of the binoculars more exaggerated.
Typically an 8 or 10 times magnification power is the preferred choice, but 12 and 15 times magnification are also available in some models.
02 | Objective Lens.
The objective lenses at the front end of the binocular. The width of the objective lens relates to the second number in the binoculars description. e.g a 10 x 42 binocular has a pair of objective lenses that each measure 42mm in diameter.
Larger objective lenses give better light transmission and allow for a brighter picture. A larger objective lens will allow the binoculars to be used in lower light conditions.
03 | Field Of View (FOV)
The width of the binoculars view. A larger FOV allows for a wider image to be seen.
This can be measured in terms of angle (degrees), or by a set distance. e.g the FOV of a binocular 8 x 42 could be 129m wide when looking at the image 1000m away. This is equivalent to 388ft wide when looking at an image 1000yds away.
04 | Exit Pupil.
The diameter of the viewable image when the eye is positioned at the correct eye relief. This is calculated by dividing the objective lens diameter by the binocular magnification. e.g for a 10 x 42 binocular divide the objective lens diameter of 42mm by the magnification power of 10 to get a 4.2mm exit pupil.
05 | Interpupillary Distance,
The distance between the two ocular lenses. This is measured from the middle of one lens to another. The interpupillary distance has a range, as the distance will change depending how open or closed the binoculars hinge is set.
06 | Eye Relief.
The distance from the pupil to the ocular lens. When at the correct distance the best viewing experience will be achieved. All Hawke binoculars are fitted with adjustable twist-up eye cups to help gain the correct eye relief distance and comfortable viewing experience.
07 | Close Focus.
The closest possible distance that the binoculars can be focused at. Binoculars with an ability to focus at close range allow for better viewing of nearby objects such as insects and garden birds.
Glass Quality and Coatings.
01 | Extra-low Dispersion (ED) Lenses.
ED lenses are the most effective way to improve image quality and stop colour fringing (chromatic aberration). ED glass allows for better concentration and direction of light wavelengths, which give a significantly sharper image and improved contrast of colours and light.
02 | Fully Multi-Coated (FMC) Lens Coating.
There are many lenses within a binoculars optical system. FMC lenses ensure that both sides of every lens have multiple layers of coating which assist with light transmission and help produce brighter images with improved contrast.
03 | BAK-4 Roof Prism.
BAK-4 is a type of glass used within the prism, which is a system of glass elements inside the binocular that ensure the viewed image is the correct orientation after being magnified. A roof prism is a more compact and sharper version of older traditional Porro prisms.
04 | Phase Corrected Coating.
The light travelling through a binocular prism is reflected several times and as such can lose its “phase”, meaning that colours can appear overlapping and produce colour fringing, also known as chromatic aberration. A phase correction coating helps to stop chromatic aberration.
05 | Silver Mirror Coating.
A silver mirror coating can be applied to elements within the prism and increase reflection. This also improves brightness and colour reproduction. This silver coatings have a reflectivity of 95% to 98%.
06 | Dielectric Coating.
Dielectric Coating of the prisms improves internal reflection even more than a silver mirror coating. This maximises the quality of visible light and produces clear, high-contrast images, similar to those seen by the naked eye.
07 | Water Repellent Coating.
Water repellent coatings significantly improve optical performance in wet conditions. The extra lens coating encourages the water droplets to “bead” and form into smaller drops that are easier to clean and will more actively run off the glass lens.
Parts and Mechanical Features.
01 | Dioptre.
Each binocular is equipped with an adjustable dioptre which is used to correct any imbalance in eye strength. Typically the dioptre adjuster is positioned on the right hand eyepiece. See bottom for details on how to set this feature.
02 | Focus Wheel.
The focus wheel can easily rotated to change the focal distance of the binoculars. All binoculars feature a central focus wheel which accurately guide and adjust the internal lenses while keeping them protected from outside elements and dirt.
03 | Twist-up Eye Cup.
With three different height settings, the twist up eye cups can be set to ensure the best eye relief for your use. Eyeglasses users often leave the twist-up eye cup in the downward position, while non eye-glasses users rotate the twist-up mechanism upright.
04 | Tripod Attachment.
Some full-sized binoculars have a tripod fitting with a standard tripod thread (1/4-20 UNC). This allows for positioning and solid mounting to keep the binoculars still when in use.
05 | Nitrogen Purged.
Binoculars are filled with nitrogen gas to ensure that no condensation or humidity is held within the optical system which can otherwise haze and cloud the optical view when moving between warm and old conditions. The nitrogen gas is sealed into the binoculars during manufacture to ensure no moisture can infringe the optics.
Focusing Your Binocular: Setting the Dioptre.
Set the dioptre adjuster to the centre position.
Close your right eye and rotate the focusing wheel until the image in the left eyepiece appears sharp.
Now close your left eye and rotate the dioptre adjuster until the image is sharp.
The binoculars have now been adjusted to your eyes.