Introduction to focimeter

A focimeter is an instrument used to measure the focal length of optical components such as lenses and concave and convex mirrors. A focimeter is actually a special telescope consisting of two lenses. A tiny light source is placed at the focus of the focimeter, and the lens group produces a magnified virtual image. The focimeter can read the focal length of the optical element by adjusting the position of the lens so that the virtual image is clear and falls on the scale.
There are generally two types of focimeters, the direct method and the indirect method. The direct method uses a fixed reference lens to focus the virtual image onto the scale, and then adjusts the position of the measuring lens to match the focal length of the reference lens, thereby measuring the focal length of the lens to be measured. The indirect rule is to measure the focal length of the component under test through two lenses or concave and convex mirrors with a known distance apart, and use the system focal length relationship of the lens group to calculate it. No matter which method is used, the focimeter can quickly and accurately measure the focal length of optical components in the laboratory or manufacturing industry, which is of great significance for the design and adjustment of optical systems.