What is a Fresnel lens?

What is a Fresnel lens?

 

For us, Fresnel lens seems a bit unfamiliar, but it is present in our real lives, for this we need to understand it further, so as to make better use of it to create value for our mankind. Therefore, today I'll talk about classification of Fresnel lenses and other related content. Hope to be able to bring more help to your lives, so as to make progress in life.

The Fresnel lens also known as thread lenses, are made from optical molding polyolefin material with thin slices, which also made of glass, one side with lens is smooth ,and the other side burn from small to large concentric circles, its texture is designed based on optical interference and disturbance shot angle, and relative sensitivity and receive requirements ;Requirements of Lens is very high. A high quality lens to smooth surface, texture clear, thickness changing with usage, 1mm, characteristic for the area, the thickness of thin and long detection distance. Fresnel lenses in many cases the equivalent of convex lens infrared and visible light, the result is better, but the cost is much lower than the normal convex lens. Used in many occasions for high accuracy requirements , such as projectors, infrared detectors, thin film magnifying glass

 

Fresnel lens can be classified according to optical design or structure ; Fresnel lens has two effects: first is focusing action; the second is to divide the detection into a number of bright area and dark area, which make the moving object making access to the detection areas can be showed thermal infrared signals in the form of temperature change in the PIR (passive infra-red detectors)

 

Classification of Fresnel lens:

Division by Design:

Positive Fresnel lens: Light rays enter from the one side, and will come out form the other side with parallel lights projected or a focused point. Focus in on the other side of light, and is a finite conjugate. Such lenses are usually designed for collimator lens (such as projection with a Fresnel lens, magnifying glass) and condenser (such as Fresnel lens for solar concentrating thermal.

Negative Fresnel lens:

As against to positive Fresnel lens, the focus and light on same side, as the first reflective surface usually will be added coating on the surface ;

 

Division with Structural

Circular Fresnel lens, Fresnel lens arrays, cylindrical Fresnel lens linear Fresnel lenses, diffraction-Fresnel lens, Fresnel reflection lens feinieerguang beam separators and Fresnel prisms.

Function of Fresnel lens

Utilize Special principle of optics, Fresnel lens will generate an alternating area of "blind zone" and "high sensitive areas" in front of the detector in order to improve its detection sensitivity.

 

When someone walked by from the lens , the infrared light generated from human beings began to turn from the "blind zone" in "high sensitive areas", which make the received infrared signals pulse input as type of a suddenly strong or weak, and so as to increase energy amplitude

Fresnel lens has two effects: first is focusing, let thermal-infrared signal reflection (reflection) on the PIR, the second role is the detection area is divided into a number of light zone and dark zone, making moving object access to detection area with a temperature change format showing in the PIR infrared signals.

In short ; Fresnel lens are equidistance of thread on the lens side, these thread which can achieve the effects of reflecting or refracting for OB Optical Bandpass in the spectral range ;Traditional Polish optical band-pass optical filter equipment is expensive. Fresnel lenses can dramatically reduce costs.

A typical example is the PIR. PIR is widely used on the siren. If you take a look at, you will find in each on the PIR has a small plastic caps. This is the Fresnel lens. Small caps are engraved the tooth line. This Fresnel lens optical frequency peak can be limited to around 10 μm (infrared radiation of human body peak).Fresnel lenses can focus through the narrow-band interference filter light on Silicon photo-grade on the active area of the detector, Fresnel lens can not use any organic solvents (such as alcohol) to clean, dust, can be washed with distilled water or plain water, then wipe with cotton wool.

Now the camera focusing screen is frosted glass Fresnel lenses, its advantages are bright and uniform brightness. When the focus, in focus the image on the screen is not clear. In line with the more precise focus, generally in the middle of the focusing screen with split image and micro Prism ring device. When you focus, the subject in the center of the focusing screen is split into two images, when combining two separate images, shows that focusing accuracy. AF SLR the standard focusing screen are generally not equipped with split-image device, but there is a small rectangular box AF area, some on the focusing screen also engraved with partial metering or spot metering area. Early AF SLR focus in a dark environment, it is difficult to see the focus box, it is difficult to determine which camera is to focus, to focus on a new SLR focusing screens glow, or focus sound, easy to confirm the focus in a complex environment. Focusing screen of different types have different purposes, the photograph may be used such as split-image focusing screen is better, with horizontal lines applies to buildings or scale-focus screen photography and document copying; middle part not only micro Prism split-image focusing screen applies a small aperture lenses, it doesn't have the disadvantages of the split-image one side bright black. Many Focus SLR camera screen user-replaceable. Also known as threaded lens.

Sum up , Fresnel lenses are also called threaded lens ; Fresnel lens is a optical components with very wide range of application, its design and manufacture design for More than one technology area ; including optical engineering, polymer engineering, CNC machining, diamond turning technology, nickel plating; optical compression molding, injection molding, casting and other manufacturing processes.