Magnification

Magnification is basically the number of times the binoculars will magnify an image so for example binoculars with 10x magnification will enlarge the image to 10x the size you would see it with the naked eye. The level of magnifying power will have an impact on how bright an image will appear so generally speaking binoculars with 8x magnification will deliver a brighter image than those with 10x magnification.  

The greater the magnification the more susceptible the binoculars are to distortion due to handshake. You will often see that the recommendation for bird watching binoculars is that you use 7x or 8x magnification, possibly 10x at the most (unless you are going to use a tripod). This is because binoculars over 10x magnification are likely to provide you with distorted vision due to slight movements in your hand.

If you are looking for high levels of magnification, without using a tripod, then there are binoculars on the market that include image stabilizing technology, at a price! Users of binoculars which incorporate image stabilizing technology rave about the clear sharp images they provide. High magnification binoculars can be hand held when they incorporate imaging stabilizing technology and images will remain sharp even in a moving vehicle.

Near / Close Focus

Close focus distance indicates the distance from which you can focus on an object. The importance of close focus is dependant on what you want to use your binoculars for. Obviously the close focus distance is far more important for nature watching than it is for long distance viewing such as astronomy.

Nitrogen Filled / Purged

Binoculars that are nitrogen filled and O-ring sealed are waterproof and fog free. It also prevents dust and dirt getting inside and helps to prolong the life of binoculars.

Objective lens

Objective lenses are the large lenses at the front of the binoculars through which the light passes through. Binoculars with larger objective diameters gather more light which will have a positive impact on image brightness. If you are looking for binoculars that are suitable for astronomy, for example, you need to be able to gather as much light as possible and will therefore need to look for binoculars with a large objective lens.

Doubling the size of the objective lens will mean the binoculars will have four times the light gathering ability but this benefit should be considered alongside other factors such as usage and the size of the exit pupil as part of your buying decision.

One of the main downsides of large objective diameters is the weight and size which is why lightweight, compact binoculars have smaller objective lenses. If you are looking for bird watching binoculars for example, that are to be hand held, you won’t want to go out and buy massively heavy binoculars with a large objective lens.

Prisms

There are two basic designs of prisms, roof prisms or porro prisms. Lightweight, compact binoculars are generally fitted with roof prisms which are lighter in weight and more portable.

The purpose of prisms in binoculars is to invert the image and the quality of the prism will have a distinct impact on the clarity of the image. Higher grade binoculars will come with multi-coated prisms or the Canon 18x50 IS Binoculars, for example, come with Vari-Angle Prism which will constantly adjust for even the slightest movement in the binoculars.  Nikon use phase-corrected-coated prisms for high resolution.

Prisms are denoted as being either BAK-4 or BK7. BAK-4 prisms are considered to be the best quality being of finer glass which is of a higher density thereby almost eliminating and internal light scattering. Better quality prisms produce sharper more well defined images.

Resolution

Resolution is a measurement of a binoculars ability to enable you to see the fine detail of the image you are viewing and is directly related to the size of the objective lenses. As a general rule of thumb the larger the objective lenses the greater the detail you will be able to see although other factors play a part such as:

·        The quality of the lenses

·        The type of lens coating

·        Correct optical alignment