A varifocal lens is a lens with a manually adjustable focal length. Devices of this type are used in cameras (they are equipped exclusively with lenses of this type) and video cameras (they can be either with a fixed focal length or with a variable one). A varifocal 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, accordingly, the image scale in the range of focal lengths. However, the sharpness of the aiming of the object and the relative aperture do not change.
Manually adjustable varifocal lens allows you to change the focal length twice, which makes it possible to adjust the camera's angle of view for the optimal image. Devices with remote control can change the focal length from 6 to 50 times. Such lenses are used for video surveillance.
Let's see what are the advantages and disadvantages of such a device as a varifocal lens.
The advantages of the device include the fact that it allows you to adjust the viewing angle directly on the spot, when installing the video camera. And, of course, after installing the camera, it is possible to adjust the focal length. This is where the advantages of such devices end. Now let's move on to the disadvantages.
A camera with a varifocal lens needs to be adjusted, which is not always convenient, since you have to constantly carry additional equipment with you (test monitor, battery, etc.). Setting up the lens is quite complicated, it is necessary to determine the optimal ratio of focal length and sharpness, and a procedure is performed with special filters (very expensive) that darken the picture. So the first downside is the complicated setup.
A varifocal lens has a lower throughput (aperture) than a fixed lens. This is especially noticeable on devices with a wide range (5-50), the image quality at dusk will be disgusting. Low aperture is the second drawback.
The third disadvantage of a varifocal lens is that it can defocus over time due to mechanical or thermal influences. As a result, additional tuning will be required after a few months.
The fourth disadvantage is the price of such a lens,it is much more expensive than the fixed one.
Summarizing, let's say that varifocal lenses, despite their shortcomings, are very popular and in greater demand than fixed ones. However, it is worth noting that the review in this article is only for cameras designed for video surveillance, because only they have a choice of fixed or adjustable lenses. Cameras and consumer camcorders use exclusively customizable optics.
