JARGON BUSTER:

Bak-4 prisms - are bigger than the alternative Bk-7 versions and reflect more light.

Dioptre – allows you to adjust for any difference between your left and right eyes. Usually located on one eyepiece or centrally opposite focus wheel.

Eye cups – these usually pop, twist or fold up and down.
Always use them extended unless wearing spectacles.

Field of view – usually expressed as the width viewed in metres from a set distance, such as 1000 metres or in degrees. (eg. 1° = 17.5m approx.) A wider angle is best but usually a bit more expensive.

Focus wheel - allows you to focus on any subject at any distance. The focus wheel is usually located in centrally.

Internal focusing - when focusing the lenses move in and out to increase or decrease their distance from the internal prisms. Without internal focussing you can see the eyepieces, connected by the bridge, moving in and out. As the name suggests, internal focusing incorporates all these moving parts within the unit, so it is easier to keep rain and dust out.

Magnification – the best for bird watching range from 7x and 8x to 10x. Anything smaller does not really get you close enough and higher is difficult to hold steady. (Unless you opt for one of the new auto stabilising binoculars). The most popular magnification is 8x

Multi-coated lens – microscopic layer coating lenses to maximise light penetration and contrast rendition.   

Numbers – these tell you the magnification and the objective diameter eg. 10x42 means 10 times magnification and a 42mm objective diameter.

Objective lens – the big ones nearest whatever you are watching. As a rule the bigger the better for light gathering and a generally brighter image.

Rubber armour – a scuff and knock resistant covering, sometimes denoted by the German abbreviation GA. It does not itself make binoculars water-resistant or dust proof.