RVI lenses with IR correction.
RVI lenses with IR correction
The requirements for a video surveillance system can only be met by using high-quality lenses that transmit a clear image. If to obtain information about the occurrence of an abnormal situation it is enough to see the outlines of what is happening, then identifying an object without a clear, sharp image is already problematic — it is possible only with the use of high-quality lenses. That is why the choice of lens — the first link in the video surveillance system — determines the efficiency of the entire system.
For a video surveillance system, image sharpness is of primary importance, and therefore this criterion should be considered first. Image quality is determined by the choice of lens material and varies significantly when using glass or plastic. In addition, important factors include the purity of lens grinding and the accuracy of their assembly into groups.
The sharpness of the image is also affected by the choice and quality of the processing of the body materials, the diaphragm, electronics, mechanics and, of course, the care with which the lenses and periphery are assembled into the lens.
Glass coating
Along with the luminosity, the light transmission capacity plays a key role. Depending on the quality of the glass and its coating, light loss due to its scattering on the surface, reflection and absorption is minimized. In this case, the lens coating plays a key role. That is why you should pay attention to whether the lenses have a coating at all, and if so, whether all of them have a coating, single-layer or multi-layer, what is the wear resistance when cleaning the lenses.
Video surveillance using infrared light
When using infrared light for video surveillance, additional factors must be taken into account. IR light has a longer wavelength and is refracted to a lesser extent than visible light. Due to this circumstance, when changing from visible light to IR, focus correction is essential.
The latest developments in video surveillance technology include day/night cameras. They operate in color mode during daylight hours, and switch to black and white mode at night using IR light. Such IR-sensitive cameras, especially in bright sunlight with a rich IR component, can transmit images with color distortion. For example, red surfaces become pink or yellow. To eliminate such distortions, filters that do not transmit IR light are built into the cameras. However, such filters often do not cut off the required dose of IR radiation, which still entails unbalanced color transmission.
RVI offers so-called day+night lenses especially for use with day/night cameras. These optics are made from special types of glass and designed in such a way that the image remains sharp in both daylight and IR illumination (wavelength of about 850 nm) without refocusing. In addition, such lenses have a built-in IR filter, which filters out IR rays even more actively the more the aperture is closed. Thus, it reliably absorbs unwanted IR light during the day, but allows visible light to pass through. The images are realistic and in natural colors. In the dark, IR illumination is activated, and the camera switches to night black and white mode. Now, thanks to special IR correction, the day+night lens provides sharp and clear images without glare with a fully open aperture. The IR filter is deactivated, and the difference in the refractive index of IR and daylight is equalized.
The art of a high-quality lens manufacturer lies in optimally combining all these criteria that determine the quality of optics. Only then will the development result in the highest quality and durability combined with a reasonable price.