Selecting CCTV Equipment
Top quality optics - Tokina
Tokina is Japanese company that has been known in the world since 1951 for its quality products used in photography. Since 1996 the company has been manufacturing special lenses for CCTV cameras. Currently the company provides the following kinds of lenses:
- with IR correction
- with automatic focusing
- with focal length from 1.4 to 1100 mm
- for cameras with 3-CCD sensors
Below we present different models, in order to facilitate the selection of the most appropriate one for specific conditions.
Tokina lens 3.3 - 8 mm - M2301
Product offer of any company manufacturing CCTV lenses must contain items with focal length of approximately 3 to 8 mm. Such basic models are perfectly suitable for camera points providing general view or placed in typical rooms. The horizontal angle of observation varies from about 80 to 33 degrees. The lenses can be used in the monitoring of premises, parking lots etc., ensuring a compromise between image details and the size of the area being monitored.
Since the M2301 lens is equipped with manual iris control, it can be used in cameras that do not have iris control function. High performance of the lens allows to use it with cameras of resolution up to 1.3 Mpx.
Focal length 3.3 mm and 8 mm
Tokina lens 2.7 - 12.5 mm - M2302
It may happen that the focal length of 8 mm is not enough, while the use of varifocal lenses with a range of e.g. 5 - 50 mm is not entirely justified. Then the optimal solution is flexible model with focal length adjustment from 2.7 - 12.5 mm, which allows to achieve viewing angle of about 22 degrees. Such a lens may be used in the facilities mentioned earlier, as well as in monitoring of corridors, narrow passages, entries.
Similarly to the former lens, it is equipped with manual iris control and can be used in cameras that do not have iris control function. High performance of the lens allows to use it with cameras of resolution up to 1.3 Mpx.
Focal length 2.7 mm and 12.5 mm
Tokina lens 3.3 - 8.2 mm - M2311
- High brightness: F0.98
- Automatic iris (DC)
- IR correction
Lens brightness informs about how much of the light passes through the lens. It is calculated as the ratio of the lens effective aperture (D) and its focal length (f). In practice, lens brightness is expressed as an F number being the inverse (f/D) of the aperture ratio. "Bright" lenses have F-numbers lower than 1.4. The M2311 lens has F0.98.
Automatic iris control allows to adjust the quantity of the light passing through the lens. A camera with lens with manual iris control has to cope with changes in lighting e.g. by adjusting exposure time. A camera with auto-iris lens first of all controls the iris, closing it in strong light or opening it up in insufficient lighting - to get the optimum image.
IR correction - in the case of typical lens different wave lengths (colors) are deflected by different angles. It is not so critical within visible light spectrum, but poses a problem in infrared range (night operation with IR lighting). The specially designed aspherical optical components of the M2311 lens allow optimum operation both during the day and at night.
Summing up, the M2311 lens is ideal for cooperation with a camera supporting iris control and operating in difficult light conditions, including necessity of IR illumination.
Focal length 3 mm and 8.2 mm
Tokina lens 2.7 - 12.5 mm - M2312
Focal length 2.7 mm and 12.5 mm
Tokina lens 6 - 60 mm - M2313
There are many installations in which the described lenses are not able to cope despite the characteristics shown earlier. An example would be monitoring of roads with reading license plates. 12 mm focal length does not allow for a narrower i.e. clear picture of the plate from a distance. Therefore, for such purpose the commonly used lenses have focal length from 5 to 50 mm. However, the M2313 model has even a wider range, from 6 to 60 mm, making it even easier to adapt to different kinds of specific conditions. It cooperates with cameras having DC control, so it may well fulfill its function in highly variable lighting conditions.
Focal length 6 mm and 60 mm
Tokina lens 10 - 120 mm - M2314
In some specific conditions the objects have to be observed from a distance. Lens with maximum focal length of 60 mm can still be "too short". It is difficult to obtain high quality close-ups. Therefore, the market offers lenses up to 100 mm maximum. The exception is the M2314, with an extra-wide range from 10 to 120 mm. It allows to see every detail even from very far away (the minimum viewing angle of the lens is only about 3 degrees). However, nothing is for free: big zoom means a big size - more than 12 cm! This is more than the length of some camera models. Therefore, the lens is also equipped with fastening to a bracket or housing, so, in fact, the camera can be screwed to the lens.
Focal length 10 mm and 120 mm
Tokina lens 4.5 - 13 mm - M2235
M2235 lens belongs to the class of lenses typically used for megapixel cameras. The manufacturer recommends it for cameras with a resolution of 3 Mpx, but high quality optical components and exceptional precision of the lens allow to use them even with 5 megapixel devices. The undoubted advantage of this model is that, unlike the competing lenses, the thread pitch of the focus ring is small, which allows very accurate focus setting in full zoom range. This is particularly important at higher resolutions, since the problem arises in the case of resolution 2Mpx or higher. Standard definition cameras are not so sensitive to focus adjustment because of limited resolution.
Tokina lens 1.4 mm - M2236
This lens of 1.4 mm focal length belongs to the group of fish-eye lenses. To obtain the appropriate focal length the glass lens is very thick and convex. The horizontal viewing angle reaches 185 degrees. This means seeing the image from behind the lens!
Application of the lens is very specific because of the shape of the image, as well as its detail. First of all, the image is circular. With a standard lens, viewing angle is about 90 degrees. When the viewing angle is 185 degrees, the field of view becomes several times larger. This allows to achieve satisfactory results only with megapixel cameras.
Below there is an example screenshot from a camera point configured for monitoring office space in a wide horizontal area. Such short focal length introduces a significant distortion of the picture, yet the user receives image of the whole room. The parameters of the image sensor have been changed to remove the excess image at the top and bottom.
The panorama with modified field of view - the M2236 lens
Tokina lenses belong to top optical devices. Wide range of products enables the user to choose the best item for any application. DIPOL is an official distributor of Tokina lenses.
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