Viewing the subject up close is not the same as viewing the subject clearly. A higher magnification makes the subject look closer, but it also narrows the actual field of view and makes it difficult to search for an object and can increase shaking caused by hand movement. It is important to choose a magnification based on your needs and ease of use, rather than just the pair with the highest magnification.
As light passes through the lens and prism, it is reflected, reducing the amount of light and making the image darker. To minimise the loss of light, a lens coating is applied. Multi-coating has multiple layers of coating, which provides an excellent effect and enables a clear, bright image.
The size of the pupil of the binoculars ( or exit pupil diameter) is calculated by dividing the effective diameter of the objective lens by the magnification. The larger the exit pupil diameter the brighter the image can be seen. As a basic rule binoculars should have an exit pupil diameter that is larger than the diameter of the human pupil however the difficulty is that the size of the human pupil changes depending on the brightness of the surroundings. Therefore when using binoculars in bright locations it is best to have an exit pupil diameter larger than 2 to 3 mm. On the other hand when using binoculars in dimly lit locations it is best to have an exit pupil diameter larger than the human pupil of 5 to 7mm.
The human pupil diameter is approximately 2 to 3 mm, therefore 7x20 binoculars with an exit pupil diameter of 2.9 mm provide sufficient brightness for general outdoor use.
In poor lighting conditions the human pupil diameter is approximately 5 to 7 mm thus when using 7x20 binoculars with an exit pupil diameter of 2.9 mm the scene will appear dark.
When using 7x50 binoculars with an exit pupil diameter of 7.1 mm that is larger than the human pupil diameter in dark conditions scenes will appear with sufficient brightness even in dimly lit locations.
Choose a pair of binoculars based on your desired application to ensure the most effective use. Generally, binoculars with a magnification between 6x and 10x are easy to use. Portability is also an important factor, especially for use in theatre; and a waterproof design is recommended if you want to do whale-watching and other outdoor activities. For spectator sports an easy-to-focus model to view fast-moving action would suit best and to ensure you select the right binocular for us discuss your application with an optics dealer when purchasing.
The exit pupil of the binoculars is the bright circle that is visible when the eyepiece lens is held approximately 30 cm away. The higher the accuracy of the lens, the greater the exit pupil appears as a circle without shadows in the periphery. Check the exit pupil size to determine the quality of the binoculars.