Focaldistance vsfocal length

Examine the target through the system and identify the group and element numbers of the smallest set of triple bars that you can resolve - both vertically and horizontally. The groups are labeled with numbers and the elements with letters.

Place the USAF resolution target at the same plane where the object of interest would be located. Ensure that the target surface is perpendicular to the optical axis of the system.

focallength是什么

Provide uniform illumination across the target. The light should be bright enough to create sufficient contrast without causing glare or reflections.

The United States Air Force (USAF) resolution target is a widely used test pattern for evaluating the resolving power of optical systems like microscopes, cameras, and lenses. The target consists of a series of patterns that decrease in size and are used to determine the resolution limits of the optical system under test.

Using the group and element identified, refer to the provided documentation for the target to determine the corresponding resolution in line pairs per millimeter (lp/mm).

Focal length

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For accurate measurement, ensure that the optical system is properly aligned and free from aberrations. The target should be in the exact focal plane, and the measurement should be taken from the center of the system's field of view.

focallength中文

In optics, the distance from the middle of the lens to its focal point. Light rays run in parallel to one another, while lenses distort light rays: a convex lens (the type that is thicker in the centre than at the edges) brings them closer together and a concave lens (the type that is thinner in the centre) forces them apart. Cameras use convex lenses to bring the light rays together to a point where they converge and the image is in focus: this is where the film or light sensitive diode goes. The more convex (or thicker) the lens, the more severely the light rays are bent and the shorter the focal length (conversely, the thinner the lens the longer the focal length). Different focal lengths create different kinds of image effects. Lenses with very short focal lengths (or wide angle lenses) allow more of the picture to be seen and emphasize foreground elements, whereas lenses with very long focal lengths (or telephoto lenses) allow less of the picture to be seen and emphasize background elements which appear to be magnified. These different effects are dramatically illustrated by a technique used in feature films called a Hitchcock zoom, where the camera tracks out at the same time as it zooms in (or vice versa), an effect used in the film Vertigo (1958).

Adjust your optical system to focus on the target. The image should be as sharp as possible before taking any measurements.

The USAF resolution target is an effective tool for verifying the performance of an optical system and can help in comparing different systems under similar conditions.