Camera lens selection

The target size of the image sensor of different cameras is different, but the common sensor specification is 4: 3 (H: V).

The imaging size of the lens needs to be greater than or equal to the camera, otherwise there will be black edges around it.

Focal length: the distance from the lens center to the image target sensor; Field of view angle: the spatial range that can be seen on the receiving element.

-& gt； When the lens imaging size is fixed, the longer the focal length, the smaller the field of view angle.

-& gt； When the focal length of the lens is fixed, the larger the imaging size, the larger the field of view angle.

< optical zoom and digital zoom >;

As shown in the figure, when optical zooming, the focal length will change, the focal width will remain unchanged, and the picture will not be blurred.

Digital zoom, the focal length is unchanged, and the focal width is enlarged manually, which leads to the change of viewing angle and blurred picture.

Aperture coefficient = focal length F/ coherent aperture d

The smaller the aperture coefficient F 1.0, the greater the light input and the better the imaging at night.

! ! The smaller the f, the better, and the larger the aperture, the better! !

When focusing on an object, it seems that the object is clear in a certain range before and after the focus, which is called;

The larger the aperture, the smaller the depth of field.

Q: Why is it that sometimes the lens is clearly adjusted during the day and blurred at night?

-Plenty of light during the day, small aperture and large depth of field, weak light and small depth of field at night, and the illumination before and after will be unclear.

(Focus can be adjusted at night)

First, the estimation method (for lenses larger than 4mm)

The sub-algorithm is used for general monitoring, for example, the distance between the person and the camera is 10 meter.

-Look at the face, 20mm or so.

-See the outline of the human body clearly. The lens is about 10 mm.

-Observing people's activities, 5 mm lens

Second, pixel selection.

Lens pixels must be greater than or equal to bolt pixels.

Manual aperture is adjusted by shutter.

Automatic aperture-video drive, DC drive

& lt scene width selection resolution >;

3m ~ 200W

2m-4.5m ~ 400W

4.5m-6m-600W

6m-8M/8M-32m ~ 1 1-40mm