About Binoculars
How Binoculars Work
In their most basic construction, binoculars consist of two lenses. The lens nearest whatever is being observed (objective lens) provides an image, which can then be enlarged by the lens closest to the viewer’s eye (eyepiece lens), by moving it closer to or further away from the objective lens.
Because the light when directed through the lenses has been refracted or bent, the time the viewer sees the image it is upside-down, and back to front . Two prisms are placed inside the binoculars, between the objective and the eyepiece to fix this.
Power, Light and Weight
The optic power is expressed as two numbers, such as 7 x 35. The first is the number of times magnification, and the second is the diameter of the objective lens. A larger objective lens will capture more of the available light and so is more useful in low-light situations.
The magnification factor shows how many times larger the object will be magnified – a number of between 4 and 7 is ample for most applications. A magnification factor larger than about 9 or 10, and the natural shaking of the human hand will be magnified to such an extent that the image can become difficult to see, and a tripod will be required.
Pricing Justification
When choosing binoculars, price is a major consideration. Several factors that affect pricing.
The first, is the type of lens and coating used; glass lenses, which are coated on each side with multiple layers, will produce a picture at high magnification which is substantially clearer and brighter than that produced by plastic lenses.
Plastic lenses, although they make the binoculars lighter, will be substantially more expensive for the same grade of picture quality. If the binoculars are to be used in clear conditions, at a low power, this may be acceptable. The more variation in lighting expected, the better quality optics, and therefore higher price tag one should expect.
The build quality will also affect the price. More rugged, shock-proof binoculars to be used in harsh conditions will cost more than those which do not need to be waterproof or shockproof.
Eye Relief
“Eye Relief” refers to the way that the eyepiece is set up with respect to the other optics in the device. Most glasses will come with eye relief between 9mm and 13mm. This is the distance between your eye and the lens before your field of view becomes limited.
If you wear eyeglasses, eye relief above 14mm becomes desirable; you will already have a certain amount of distance between your eye and your eyeglass lens, which you can not change. Because of this, if your chosen optical device has a small eye relief, then you will have a very restricted field of view, and miss out on most of the picture!
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