How do SLR cameras take particularly dark photos?

SLR camera is the abbreviation of single-lens reflex camera. Photographers control a lot of space, which is almost arbitrary. The photos taken by it are particularly dark because of insufficient exposure time, mainly for the following reasons:

1, camera setting or parameter adjustment is incorrect, for example, exposure compensation is negative, and full exposure cannot be achieved when setting indicators manually.

2. The measurement is inaccurate. For example, when the central button is used for metering, the bright metering area will mislead the exposure of the camera.

3. The metering system of SLR camera itself is defective. Although this possibility is relatively small, it can be compared with automatic fool mode shooting.

The scene is really terrible.

5. Is there any filter on the lens that affects the exposure and the luminous flux?

6. The electronic display screen of the camera is covered with a protective film, which makes the photos feel particularly dark when they are played back or watched in real time.

All of the above may affect the exposure and darken the photo, or the combination of the above two may darken the photo.