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菲涅尔透镜的作用


Finel lens makes use of the special optics principle of lens to create an alternating "blind area" and "high sensitive area" in front of detector, so as to improve its detection and reception sensitivity. When someone walks past a lens, the infrared ray emitted by the human body continuously alternates from the blind area to the "high sensitive area", which makes the received infrared signal input in a strong and weak pulse form, thereby enhancing its energy amplitude.
There are two effects of Finel lens.
We are focused on the role of pyroelectric infrared signal, the refraction (reflection) in PIR, second is the detection area is divided into a plurality of light and dark, the moving object enters a detection area to temperature change in the form of infrared signal on PIR thermal changes. Finel lens, simply speaking, is equidistant tooth profile on the side of lens. Through these teeth marks, we can achieve the role of optical band pass (reflection or refraction) in the specified spectral range. The traditional band-pass optical filter is expensive. The Finel lens can greatly reduce the cost.
A typical example is PIR. PIR is widely used on the alarm. If you take a look, you'll find a small plastic hat on every PIR. This is the Finel lens. The interior of the small hat was carved on the teeth. The Finel lens can limit the peak frequency of incident light to about 10 microns (the peak of human infrared radiation).
Fresnel lens can focus the light passing through the narrow-band interference filter to the photosensitive surface of the silicon photoelectric two level detector. The Finel lens can not be wiped with any organic solution (such as alcohol). When it is dusting, it can first wash with distilled water or ordinary clean water and then wipe it with absorbent cotton.
Now the camera to the focus screen is a grind glass Finel lens, its advantages are bright and uniform brightness. The focus is not in time, and the imaging on the focus screen is not clear. In order to match the focus more accurately, a split image and a microprism device are usually installed in the center of the focus screen. When the focus is not punctual, the object is split into two images in the center of the focus screen, and when the two split images merge into one, the focus is accurate. The standard of AF single lens does not have a splitting device to the focal screen. Instead, it has a small rectangular box to represent the AF area. Some of them also have local metering or spot metering area on the focal screen. Early AF SLR in low light environment in focus, it is often difficult to see the focus frame, it is difficult to judge the camera is to what point as the focus of the new generation of SLR on the screen on the focus of the light, or focus voice prompts, easy to confirm focus in a complex environment. Different focusing screens have different uses, such as crack like portrait may be better on the screen with the horizontal and vertical line or scale on the screen for the building of photography and file copy; the middle part not only micro crack like edges on the screen for small aperture lens, it does not have a crack like the disadvantage of black light side side. Many SLR cameras can be replaced by users themselves. It is also called a threaded lens.