A convex lens causes light parallel to the principal optical axis to converge at a point, which is called the focal point.

When u>2f; an inverted, reduced solid image;

When f<u<2f; an inverted, magnified solid image;

When u<f; an orthogonal, magnified virtual image. (Note: u is the object distance; f is the focal length)

Double focal length divided into real and imaginary (when u<f, an imaginary image; when u>f, a real image)

Double focal length divided into large and small (when u<2f, an enlarged image; when u>2f, a reduced image)

When the convex lens forms a real image, the object is close to the image is far away large; the object is far away from the image is close to the image is small.

When a convex lens forms an imaginary image, the object far away is far away.

The distance between the object and the image is greater than 4f.