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Something about lenses |
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Monofocal or fixed focal lenses
Vari-focal or variable focal length lenses |
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Something about lenses |
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Monofocal or fixed focal lenses
Vari-focal or variable focal length lenses |
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A good lens is a must if you want a good picture, but you must also choose the right lens to get the picture you want. And of course you should choose the lens giving you best value for your money.
Ernitec has all the lenses you need and by close co-operation with our Japanese partners, including visits to key customers all over Europe, we ensure that any new needs or developments will be available for our customers as soon as possible.
To help you select the correct lens here is a brief guide of what is an extensive subject.
Iris regulation
The iris regulates the amount of light passing through the lens. This can be regulated:
Manually, where you simply have to regulate the iris with your fingers on the lens. You only use these lenses when it is normally not necessary to regulate the iris. They are perfect for many in-door applications where light does not change.
Automatic regulation
Automatic regulation - Auto-iris lenses - where the iris will be regulated automatically according to
the amount of light available. They are available in two versions, normal auto-iris lenses where the
lens itself regulates the iris based on information from the camera and direct-drive lenses where the
camera regulates the lens. Direct drive lenses are a little cheaper than normal auto-iris lenses and
are equally suitable with many modern cameras. With the genious easy to click on Ernitec E-Con Auto Iris Converter you can easily convert any Ernitec direct drive lens into an auto iris lens. This way you only need to keep direct drive lenses on stock.
Format
The size of the CCD chip can be 1" (one inch), 2/3", 1/2", 1/3" and starting to be as small as 1/4". For example, a 2/3" lens will be larger and more expensive than a similar 1/2" lens. Best value for money is buying a lens with the same format as the camera, but you can always use a lens with a larger format than your camera. However, not the other way around, using e.g. a 1/3" lens on a 1/2" camera.
Max Aperture or F-value
This figure tells how much light the lens will pass through with fully open iris. The smaller the number the more light it will let pass through.
F-value below 1 is unusual (and normally expensive) and only used when the camera is used in the dark, or only little light is present.
ND filter
ND filter means Neutral Density filter and makes it possible to limit the amount of light passing through the lens. A normal maximum ND filter will correspond to an F-value of 360 and it is necessary if the camera is used outdoor and must function both during bright sunlight and during night.
Aspherical
This means that one or more lens elements are not spherical. By far the majority of lens elements are spherical, but the ideal shape is parabolic which is called aspherical. By using aspherical lens elements you normally get better quality, better specification and a smaller lens, but prices will also be higher.
Mount
The mount on most current CCTV lenses is either C or CS-mount. Which one to use depends on the camera, but now many cameras have both C- and CS-mount. A C-mount can be converted to a C
Monofocal or fixed focal lenses |
 Data Sheet |
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These lenses have a focal length, which cannot be changed. They have the lowest price and are fully usable if you know beforehand what focal length you need, and the picture you want can be obtained by one of the focal lengths available. |
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Vari-focal or variable focal length lenses |
Data Sheet |
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On these lenses the focal length can be changed until you have exactly the picture content you require. After that you use them exactly as a monofocal lens. They are a little more expensive than monofocal lenses, but they have the advantage of supplying exactly the picture you want and you only need to use (and stock) 2 - 3 different lenses. |
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Zoom-lenses |
Data Sheet |
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These lenses are in fact equal to Vari-focal, except for the important difference that when you change focal length, focus is maintained, which is not the case (and not needed) for Vari-focal lenses. Since they are rather expensive they are normally only used when the focal length needs to be changed on a regular basis, as in motorised zoom lenses. |
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E-Con Auto Iris Converter |
Data Sheet |
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The external easy-click-on auto iris circuit - E-Con - makes a direct drive lens into an auto iris (video driven) lens in a second. With the E-Con (Ernitec economic auto iris converter) there is no need to keep auto iris lenses on stock. In future, you only need to stock direct drive lenses. By using the E-Con, the Ernitec fixed focal, varifocal, or motorised zoom direct drive lenses, are converted for video control. The very compact E-Con is available in versions with or without standard 4 pin connector plug. The E-Con has adjustable Level and Automatic Light Compensation (ALC) for improved performance in strong backlight. |
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| EJEHSA Holmberg 4102 - C.P. 1430 Buenos Aires, Argentina |
Phone/Fax (+54 11) 4546-0129 /
0146 & 4544-4094 |
AB 10/04/2002 03:34:56 p.m.
