A binocular uses the concept of placing a set of two convex lenses one behind the other. While one lens catches the light rays and makes an image closer to the second lens. While we view through the second lens it looks closer and brighter. The first one is objective lens as it is closer to the object and the second one is the magnifying lens.
A binocular has two such sets one for each eye. However the drawback on the above setup is that due to the nature of convex lens the image would be upside down. Hence to rotate the image and to provide a natural view to the human eye, a pair of prisms is placed inside each eye, thus making the image in proper direction and also magnifying it. Due to this nature and requirements needed for binocular, they are usually heavy.
There are far more advanced developments recently in the field of Binoculars. One of them is the night vision binoculars. It is natural for a lens to capture light rays but during night it is very low and a lens can only do that much. The question is how to amplify it and electricity is something that could be amplified, the conversion of one form of energy to another plays a big role here. Thus the light particles which are made up of photons are converted to electrons by a photocathode. These electrons are then amplified by a photomultiplier and they hit a phosphor screen. This is more like our old cathode ray television, when the electrons hit the screen they are converted back to tiny flashes of light, thus creating the image. Now one more question remains unanswered is why the image looks green. This is actually intentional. When the photons arrive at the lens they are of multiple colors but the colors cannot be preserved when they become electrons. Hence the light is actually black and white only. However the screen is made to show green pictures as the human eye can view green much easily for longer periods.
These are again another special type of binocular when there is hardly any light for example in the jungle during the night and it is quite impossible to sight animals even with night vision binocular. The heat based binocular look for heat radiation. Hot objects emit infra-red rays which are captured and converted to visible light, thus providing an image for viewing.
Deep in jungles when people go for hunting, they use hunting binocular. These have a good field view to sight animals over a wide range. There are various factors as well in binocular like magnification capacity, diameter, eye relief etc. which have to be considered.
Depending on one’s needs one has to buy the best binoculars depending on the purpose of usage and before planning buy read a good binocular buying guide. This would help in identifying the specifications and parameters one would need and also read proper night vision binocular reviews and hunting binocular reviews in deciding exactly what brand and make of binocular to buy.