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Fresnel Lens Function
- Oct 16, 2018 -

Fresnel lens function

Fresnel lenses are in many cases the equivalent of infrared and visible lenses. They work well, but cost much less than normal lenses. It is mainly used for occasions where the accuracy is not very high, such as slide projector, thin film magnifier, infrared detector, etc.
Fresnel lens USES the special optics of the lens to produce an alternating "blind zone" and "high sensitivity zone" in front of the detector to improve its detection reception sensitivity. When someone passes in front of the lens, the infrared ray emitted by the human body continuously passes from the "blind area" to the "high sensitivity area", so that the received infrared signal is input in the form of strong or weak pulse to strengthen its energy range.
Fresnel lens has two functions: one is focusing, i.e. refraction (reflection) of thermoluminescent infrared signals on PIR, and the second is to divide the detection area into several bright areas and dark areas, so that moving objects entering the detection area can change with temperature

Fresnel lenses
The changed form of the thermolation infrared signal is produced on the PIR.

Fresnel lenses, simply, have an equidistant ridge on one side of the lens, through which the band pass (reflection or refraction) of the specified spectrum can be achieved. The traditional bandpass optical filter for polishing optical equipment is expensive. Fresnel lenses can greatly reduce costs.

A typical example is PIR. PIR is widely used in sirens. If you take a look at one, you'll find a small plastic hat on each PIR. This is a Fresnel lens. The inside of the little cap was marked with teeth. The Fresnel lens can limit the peak frequency of incoming light to about 10 microns (the peak of human infrared radiation).
Fresnel lens can focus the light passing through the narrow-band interference filter on the photosensitive surface of the silicon photoelectric secondary detector. Fresnel lens cannot be wiped with any organic solution (such as alcohol).
The focusing screen of today's cameras is all frosted glass Fresnel lenses, which have the advantage of being bright and even in brightness. The image on the focusing screen is not clear when the focus is off. For more accurate focusing, a split image and a micro edge ring device are usually installed in the center of the focusing screen. When the focus is inaccurate, the image in the center of the focus screen of the subject is split into two images. The standard focusing screen of the AF SLR generally does not have a split picture device, but is engraved with a small rectangular box to represent the AF area, some right
Fresnel lenses
The focal screen is also engraved with local metering or spot metering areas. In the early AF single-lens reflex machine, when focusing in a dark environment, it was often difficult to see the focus frame, so it was difficult to judge which point the camera was focusing on. The focus on the focus screen of the new-generation single-lens reflex machine would be luminous, or it had the sound prompt of focusing, which was convenient to confirm the focus in a complex environment. Different types of focusing screens have different USES. People may use a split image focusing screen better. The focusing screen, which has no split image in the middle and only a slight edge, is suitable for small aperture lenses. Many single-reverse camera can be replaced by users themselves. Also known as screw lens.

Author:Bunny Sun