The first binoculars were invented about 400 years ago. There are now several hundred different models of binoculars manufactured and sold throughout the world. Although the concept of seeing a magnified image with your own eyes has not changed, there are two distinctly different types of binoculars: prism binoculars and Galileo binoculars
The majority of binoculars sold today use convex lenses for both the objective lens and eyepiece lens. They are called prism binoculars, because prisms are used to "correct" the inverted image.
Because of the porro prisms, the light passing through forms a "Z" shape before reaching the eye.
When using roof-shaped prisms, called Roof (or Dach: meaning roof in German) prisms, the light passes through in a straight line, which makes it possible to design compact binoculars.
The concept used in the telescopes made by Galileo Galilei in the 17th Century is used in these binoculars. Because concave lenses are used for the eyepiece lenses, prisms are not needed to correct the images. Also known as opera glasses, this type is used for looking at objects not too far away.
Magnification refers to the ratio of the size as seen with the naked eye and size obtained with the binoculars. For example, if a pair of binoculars has 10x magnification, an object will be enlarged 10 times. In other words, something 100 meters away will look 10 meters away through the binoculars.
A 1,000 mm telephoto lens for a camera will provide five times higher magnification than a 200 mm lens. The same applies to binoculars, in that an object is enlarged five times more with 20x magnification binoculars than with 4x magnification binoculars. The only difference is that, while a telephoto lens must be wide enough to magnify the image for the fairly wide aperture of the camera, binoculars need only magnify the image for the relatively smaller iris of the human eye. Say for example you have 12x magnification binoculars. To get the same enlarged image using a 35 mm Single lens reflex camera, you would need to use a 700~800 mm telephoto lens. Different types of binoculars: prism binoculars and Galileo binoculars.
How clearly the binoculars let you distinguish details is called their resolving power. Because the unit area of conic vision cells in the retina of a human eye is low, no physical training will be able to increase, up to a point, the resolving power. The only way to increase it is to look through a good pair of binoculars. If you use 10x magnification binoculars, you will have 10x more resolving power than normal.
Not all binoculars will provide the magnification ratio and resolving power indicated on the instrument. When there is too much aberration, there is not enough resolving power. No matter how superior the binoculars may be, the resolving power will decrease because of image shake. The larger the magnification ratio, the more the hands will shake that image. In general, binoculars with magnification of over 10x are not recommended for hand-held use. To eliminate this problem, Canon has adopted its superior optical technologies gained in developing camera lenses. In addition to using the doublet field-flattener, UD lens and aspherical lenses to achieve ideal resolving power, Canon has used its own original image-stabilization technology (in the IS series), which greatly controls hand shake. It is because of these technologies that with Canon binoculars, each feather on a bird’s wing comes in crisp and clear.
The optical structure of each model of binoculars is different, so even if the magnification rating is the same, how much view the pair of binoculars can pull in will differ. The width of the view you can see through the binoculars is called the field of view. For bird watching in a large forest, using a wider field of view will be more useful.
This is the view through the binoculars and it is measured from the centre of the objective lens and expressed in degrees (angle). The lower the magnification the binoculars have, the wider the real field of view and the higher the magnification, the narrower the field of view. Because of this, it is hard to compare the real field of view of binoculars with that of binoculars of different magnification rating.
This value is based on a calculation laid out in the ISO 14132-1:2002 standard and represents the field of view you will see looking through the binoculars. It is comparable even among binoculars of different magnification. In general, if the apparent field of view is more than 60°, it is considered a wide field of view.
Brightness varies from one model of binoculars to another. Brightness varies with the price and size of the binoculars. There are many degrees of brightness according to ones needs.
The bright circle visible when the eyepiece lens array is viewed about 10 inches away from the eyes is called the exit pupil. The diameter, measured in millimetres, is called pupil aperture. The larger the exit pupil, the brighter an image the binoculars make, and the brightness is expressed by the square of the aperture of the exit pupil.
Human pupils are about 2-3 mm at most when bright, and the binoculars exit pupils should be about 3 mm. At night, our pupils dilate to about 7mm, so it is desirable to have binoculars with large exit pupils if they will be used at night. However, the disadvantage is that such binoculars tend to be big and heavy.
The diameter of the objective lens, which the light passes through, is called the available aperture of the objective lens. If the magnification is the same, the larger the available aperture of objective lens, the brighter image seen through the binoculars. This is the same effect as when a telephoto lens has a very large lens diameter. The relationship of the three is:
Aperture of Exit Pupil = Available Aperture of Objective Lens / Magnification.
The ideal binoculars are ones that make you forget you are looking through binoculars. If you purchase a pair with a wide field of view, and the image quality is superior (enough that there isn’t much difference from looking with the naked eye), you will have many enjoyable hours of use. Some people have the misconception that because they only concentrate on the middle of the lens, even if the outer part is blurred, it really will not matter. Normally, the retina projects aberration-free images, so when you view blurred images, the brain tries to disregard them. If you consciously try to reject the blurred images for a long period of time, there is a chance that you will become very tired and even sick. It is very hard to determine the image quality with just a spec sheet. The easiest and surest way is to actually look through the binoculars. Please keep the following points in mind when purchasing binoculars.
Binoculars use two lenses parallel to each other. However, if alignment during manufacture is not perfect, or owing to shock during transport, the lenses may become just a bit off. If that happens, you will see two images. Even if you get the binoculars fixed, the lenses will tend to slip with just a slight jolt. Such binoculars are not recommended.
Make sure that the lettering on a sign or the thin branches on trees are crystal clear. Also, make sure that the lights at night and the stars are not blurred and the shapes are not distorted. It may be difficult to know how clear the image is by looking through only one pair of binoculars. Try looking through several, and you will be able to tell the difference.
When you look at a white object, a rainbow-type ring appears. Called chromatic aberration, the image quality usually decreases, and occurs with binoculars with larger apertures and higher magnification. Also, because of the coating and different lenses used for the binoculars, the colours may change. Point the binoculars at a white image and check to see how white the image is. In order to prevent discoloration, Canon has adopted the UD lens (15X50 IS AW, 18X50 IS AW, 10x32 IS, 12x32 IS and 14x32 IS) from the EF lens series, which is known for its superior optical technology. In addition, with the "super spectra" coating, we guarantee bright and clear images.
There are more binoculars with a wide field of view to meet the demands of consumers. However, there are cases where the binoculars were "forced" to have a wider field of view, which causes the image quality around the edge of the lens to decrease. When this happens, most of the time it is caused by curvature of the field. Point the binoculars at a wall, focus on something simple, and check if you can see clearly all round. If the curvature of the field is large, the edges will be blurred. It is not recommended to purchase such binoculars. To greatly decrease the curvature of the field, Canon uses a field-flattener lens and an aspherical lens. With Canon binoculars, you will have beautiful image quality all round.
When looking through the binoculars, there are times when the perpendicular lines of windows of a building or bricks seem warped around the edge of the lens. This is called distortion. When the distortion is great, not only will the entire object seem distorted, but when you move the binoculars, it will seem as if the object were flowing, making it very hard to see. Canon uses high-precision aspherical lenses to correct the distortion.
Almost everybody who has ever used binoculars at sporting events or concerts has experienced how much the images shake, and you feel that the binoculars are useless. The main complaint of users has been image shake. The higher the magnification, the larger the image shake. In general, any binoculars with over 10x magnification should not be used for a long time. The best solution in the past was to use a tripod. However, tripods are bulky and can't be used everywhere. Even if you need a pair of binoculars of over 10x magnification for bird watching, the most you would want to use since you walk around a lot would be something of 7x or 8x magnification.
Canon is the world's first maker to use an active optical image stabilizer for IS series. Because the optical system compensates for movement and is controlled by a microprocessor, hand shake is eliminated. As a result, even with over 10x magnification, a tripod is not needed. And they can even be used while viewing from a moving platform.
Canon's 10x30 IS II, despite its image stabilizer and full size, weighs only 600g. Because a tripod would weigh a couple of pounds, the burden is cut down considerably. The 15x50 IS AW and the 18x50 IS AW are designed with a sealed construction that suits them for outdoor use, even in the heaviest rain conditions. They are built for ALL WEATHER (AW) action.
Presently, there are three makers, including Canon, selling binoculars with image stabilization technology.
Two sensors detect horizontal and vertical shaking respectively. The two Vari-Angle Prisms in both the left and right telescopes are controlled by a microprocessor to instantly adjust refraction angle of the incoming light. This system is used in Canon's IS Binoculars.
Advantages: compact, light; immediate response after the image stabilizer is activated (the system is activated as soon as the button is pressed); stable image even when panning.
Disadvantage: requires batteries.
This is similar to the Vari-Angle Prism type, except the optics used to correct the shake are regular lens elements and their movement is controlled within a suspended system - like the Image Stabilizer found in Canon's EF lens range.
Advantages: better clarity and correction of more extreme movement, such as the rocking of a boat or slow breathing motion.
A high-speed motor-driven gyroscope is attached to a prism. No matter how much the binoculars are shaken, the image will remain stable. This system is used in Fujinon's Stabiscope S1240 and S1640.
Advantage: extremely resistant to heavy shaking or movement. Disadvantages: one minute delay while the 12,000 rpm motor is starting up; tend to be heavy; this system is unable to distinguish between shake and panning, therefore image is not stable when panning; requires batteries.
The prism system is tied-in with the Cardanic Suspension system, which prevents the prisms from moving no matter how much the binoculars are shaken. This system is used in the Zeiss 20x60S Professional.
Advantages: no batteries required because of mechanical system; immediate response after the image stabilizer is activated (the system is activated as soon as the button is pressed).
Disadvantages: tend to be heavy; this system is unable to distinguish between shake and panning, therefore the image is not stable when panning.