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Objective incident pupil diameter and focal length ratio, known as the relative aperture, expressed in F, F is known as the aperture number, the relative aperture determines the ability of the lens to transfer energy (i.e., the ability to transfer the light force) according to the lens the size of the light force of the different lenses are generally divided into low-light lenses (F6.3 or less), ordinary lenses (F5.6-3.5), the strong light lens (F2.8-1.4), the ultra-strong light lens (F1-0.8).

 The optical system's field of view is the center of the incident pupil and the edge of the incident window cone angle, which determines the range of optical systems can image.

Refers to the unevenness of illumination in various places on the image plane. Relative illuminance for the center of the illuminance and the ratio of the four corners of the illuminance.

Resolution refers to the lens is able to distinguish the details of the object's ability, in general, you can use the visual method to determine the resolution, the method is to let a standard pattern resolution plate through the lens under test imaging in the Sensor, with the computer to determine the center of the four corners of the "sunflower center" degree of interference. The smaller the interference range, the higher the resolution

Can be photographed clearly at the same time the depth of space known as the lens imaging space depth, that is, the depth of field. Depth of field and focal length, F number, resolution. Lens focal length is long, the smaller the depth of field; the shorter the focal length, the greater the depth of field; F number is smaller, the smaller the depth of field; F number is larger, the greater the depth of field; resolution is lower, the smaller the depth of field; resolution is higher, the greater the depth of field.

 Refers to the phenomenon that the corners of the image surface is blocked, often caused by the camera shell stop light, should be based on different sizes of Sensor selection of the appropriate lens.

 Generally used along the optical axis to move the lens back and forth to focus, the structure of the screws to achieve that is to focus on the lens twisted to make the object a clear image, usually divided into manual focus and autofocus (AF).

TTL(Total Track Length)

 ① optical total length TOL, from the first lens of the optical system to the length of the imaging surface;

② institutional total length TTL, from the top of the lens barrel (Barrel) to the length of the imaging surface;

③ Measured length MTTL, from the top of the lens barrel (Barrel) to the PCB surface of the measurement size.