What is the relationship between object distance and focal length?

The object distance is more than twice the focal length, forming an inverted miniature image.

The object distance is equal to twice the focal length, forming an inverted image.

The object distance is less than twice the focal length, but more than twice the focal length, forming an inverted enlarged image.

The object distance is equal to a focal length, and no image is formed.

The object distance is less than a focal length, and the virtual image is vertically enlarged. Except the last one, the front is full of real images.

Let's learn the focal length.

Focal length is a measure of light convergence or divergence in an optical system, which refers to the distance from the optical center of a lens to the focal point of light convergence. It is also the distance from the center of the lens to the imaging plane such as the backplane or CCD in the camera.

An optical system with a short focal length has a better ability to collect light than an optical system with a long focal length. Simply put, the focal length is the distance from the focal point to the vertex of the mirror. The focal length is formed by the optical lens of the camera lens.