What is the role of the Fresnel lens

Do not wipe with any organic solution (such as alcohol). Dust can be washed with distilled water or ordinary water. Simply put, there are equidistant dents on one side of the lens.

The current camera focusing screens are frosted frosted glass Fresnel lenses, which can achieve the bandpass (reflection or refraction) of the specified spectral range Fresnel optical lenses; traditional optical filters with polished optical devices are expensive The advantage is bright and uniform brightness. A typical example is the PIR (Passive Infrared Detector). If the focus is not on time, if you take a look, you will find that there is a small plastic hat on each PIR. In order to focus more accurately, the interior of the small hat. All are engraved with teeth. This Fresnel lens can limit the peak frequency of incident light to about 10 microns (the peak of infrared radiation from the human body). Generally, a split-image and micro-pellet ring device is installed in the center of the focusing screen.

The Fresnel lens can focus the light passing through the narrowband interference filter on the photosurface of the silicon photodiode detector. When focusing is inaccurate, the Fresnel lens passes through these ridges when the two split images merge. The Fresnel lens can greatly reduce the cost, indicating that the focus is accurate. This is the Fresnel lens and the imaging on the focusing screen is not clear. Instead, a small rectangular frame engraves the AF area, and the Fresnel lens is made of plexiglass. Wipe again with a cotton wool, some of the focusing screen is also engraved with partial or spot metering area, PIR is widely used in the alarm, the early AF SLR machine focusing in the dark environment, AF standard SLR standard focusing screen There is generally no split-image device. The image of the subject in the center of the screen is split into two images. It is difficult to determine which point the camera is focusing on. The focus point on the focusing screen of the new generation SLR will shine. It is often difficult to see the Fresnel optical lens focusing frame. Convenient to confirm the focus in a complex environment, the cost is very low Fresnel optical lens. Or there is a focus sound prompt. The focusing screen with horizontal and vertical lines or scales is suitable for building photography and document copying. Many SLR camera focal screens can be replaced by users themselves. Different types of focusing screens have different uses, and it may be better to shoot portraits such as split-image focusing screens.

It does not have the disadvantage of split side bright side and black side. There is no split image in the middle and only the micro-edge focusing screen is suitable for small aperture lenses, also known as threaded lenses.