Variofocal lens: advantages and disadvantages

A varifocal lens is a lens with a manually adjustable focal length. Instruments of this type are used in cameras (they are equipped exclusively with lenses of this type) and video cameras (can be both with a constant focal length and with a variable one). The variofocal lens consists of a single optical system, the components of which are mechanically moved relative to each other, resulting in a smooth change (adjustment) of the focal length and, correspondingly, the scale of the image in the range of focal lengths. However, the sharpness of the object's focusing and the relative aperture do not change.

Variofocal lens with manual adjustment allows you to change the focal length twice, which makes it possible to adjust the camera angle to the optimal image. Devices with remote control can change the focal length from 6 to 50 times. These lenses are used for video surveillance.

Let's see, and what are the advantages and disadvantages of such a device, as a variofocal lens.

One of the advantages of the device is that it allows you to adjust the viewing angle directly on the spot, when installing a video camera. And, of course, after installing the camera, it is possible to adjust the focal length. On this merit of such devices end. Now let's look at the shortcomings.

A camera with a varifocal lens needs adjustment, which is not always convenient, since you will have to carry additional equipment with you all the time (test monitor, battery, etc.). Adjustment of the lens is quite complicated, it is necessary to determine the optimum ratio of the focal length and sharpness, and the procedure is performed with special filters (very expensive), which obscure the picture. So, the first drawback is a complicated setting.

The variofocal lens has a worse bandwidth (luminosity) compared to permanent lenses. This is especially noticeable on devices with a wide range (5-50), the image quality at dusk will be disgusting. Low light-gathering is the second disadvantage.

The third disadvantage of the variofocal lens is that it eventually defocuses from mechanical or thermal influences. As a result, after several months, an additional adjustment will be required.

The fourth drawback is the price of such an objective, it is much more expensive than a fixed one.

To summarize, let's say that variofocal lenses, despite their shortcomings, are very popular and are in great demand than fixed ones. However, it is worth noting that the review in this article concerns only cameras intended for video surveillance, because only they have a choice of fixed or customizable lenses. In cameras and camcorders only customizable optics are used.