Analysis and Introduction of Camera Modules (II)
2020-04-17
3. Optical technology related to camera module
focal length:EFL （Effective Focal Length）It is generally represented by f.
Definition: The distance from the center of the lens to the focal point where the light is concentrated.
Field of view angle:View Angle （Field Of View）Generally, W is used to represent half perspective.
Definition: The opening angle of the center of the entrance pupil or the opening angle of the center object of the exit pupil.
aperture
Definition: The part used to control the aperture size of the lens to control the depth of field, lens image quality, and the amount of light entering in collaboration with the shutter, the f-number of the aperture = the focal length of the lens / aperture of the aperture, the influence of the aperture on the photo: the larger the aperture, the greater the amount of light intake, the smaller the depth of field, and the smaller the f-number.
depth of field
Depth of field is related to the focal length of the lens: lenses with long focal lengths, lenses with small depth of field and short focal lengths, and lenses with large depth of field.
Depth of field is related to aperture: the smaller the aperture, the deeper the depth of field, the larger the aperture, the shallower the depth of field, and then the depth of the foreground will be smaller than the final depth of field, i.e., after focusing, the scene will become sharper at a slight distance before the focal point, and the scene will be clear at a longer distance after the focus.
CRA (Principal Ray Angle)
The angle formed from the incident light from the main optical axis of the lens to the normal of the lens on the surface of the chip
The smaller the CRA, the more refraction and the less reflection, the better the effect.
resolution
Definition: Reflects the ability of an optical system to recognize the details of an object. It is the most important indicator of the imaging quality of the optical system.
4. The composition of the lens
The composition of the lens is a lens structure, which is composed of several lenses, generally plastic lenses, glass lenses, and usually the lens structure used for cameras is: 1 P.2P. 1 G1 P. 1 G2P. 2G2P. 4G, etc., the more lenses, the higher the cost; glass T lens is more expensive than plastic, so a good quality camera should use a co-separation lens, the imaging effect will be better than the plastic lens, most of the camera products on the market now in order to reduce costs, generally use plastic lenses or semi-plastic and semi-glass lenses.
Optical
Main advantages: 1. Good light transmittance of optical glass. 2. The temperature coefficient of thermal expansion and refractive index is much lower than that of optical plastics.
Main disadvantages: 1. Optical glass generally forms a spherical surface, and the correction of spherical aberrations, comet aberrations, distortion aberrations, astigmatism and other aberrations is limited. 2. Optical glass has high density, heavy weight, high cost and many processes.
Optical plastics
Main advantages: 1. The surface shape of the aspheric lens is determined by the polynomial, and the radius of each point on the surface is different, by introducing the aspheric surface into the optical system, it can correct the spherical aberration, coma aberration, distortion, astigmatism and other aberrations, and improve the image quality of the optical system. 2. Plastic aspheric optical components have the advantages of easy forming, light weight, low cost and good performance, and have very broad application prospects in medicine, industry, military, photography, and other fields.
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