Binoculars being an essential safety element, your choice should be made carefully, the most important factor being accuracy and clear field of vision. Binoculars are defined by their optical parameters : a 7 X 50 model for example magnifies 7 times and its exit lens has a 50 mm objective diameter. Plastimo has paid particular attention to the factors which contribute to the overall view and to your comfortable navigation.
Some helpful hints To help you select your binoculars. Magnification : this indicates how powerful the binoculars are, and also indicates the apparent magnification of the subject observed. With a magnification X 7, a seamark situated at 700 m distance seems to be 100 m away. An instrument with a X b magnification is insufficient to be used outdoors ; beyond 10, the movements of the body are amplified and the image becomes unsteady, which make the binoculars difficult to use, especially at sea. Objective diameter : expressed in millimetres. The larger the objective diameter, the brighter the light through the binoculars. A diameter of 50 mm is considered as a maximum. Field of view: expressed in metres or degrees, it indicates the scope one can see through the binoculars, from a 1000 m distance. The larger the magnification, the more reduced the field of view. Exit pupil : expressed in millimetres. This is the small black circle one can see through the exit lens, when binoculars are held at about 30 cm. The larger the diameter, the better the brightness. Ideally, one should select binoculars with a 7 mm exit pupil, as this is the maximum dimension of your eye's pupil at night. You will thus have no loss of image, even in the worst brightness conditions. coating on lenses : non-coated lenses loose about 30 % of the light, which affects the brightness and creates hazy or slightly iridescent contours. Coating of lenses reduces the amount of light lost by refection as it passes through the surface of the glass (in particular when light is insufficient. Coating of lenses improves light transmission immensely and filters some of the UV rays.
| | Coated surfaces | Features / performance | UV-ray / filtering rate | | Magenta Surfaces | 1 or 2 and 5 | Better light transmission. | 15% | | Magenta + | Surfaces 1 or 2 and 3, 4, 5 | Blue/purple aspect on objective lenses. | 30% | | Fully | All surfaces | Same as above, plus a much improved | 40% |
| | crispness of image. | | | | | Blue/purple aspect on | | | | | objective lenses. | | | | | | | | Multi | Fully coating, with additional special coating on some lenses. | | | | Extra benefits : reduced colour distortion and/or UV-ray filtering. | | | | | | | | Teal aspect on | Surface 5 | Quality equivalent to Magenta+, with | | | objective lenses. | | warmer colours (reddish tones. | | | Green aspect on | Surfaces 2 and 5 | This coating offers the most natural and | 55% | | objective lenses, | | brightest image, | | | Red aspect on | Surface 5 | Provides a crisper image (but affects | | | objective lenses. | | colours, which turn bluish) | | | | | | | | Prisms | | | | | BAK-7: prism in borosilicate. | | | | | BAK-4: prism in baryum. Glass quality superior to BAK-7. | | | | | BAK-4 prisms have a much broader refraction index and therefore let | | | | | more light through with less brightness loss or distorsion. | | | |
|
