# Object micrometer

An **object micrometer** is a micrometer for determining length in light microscopy . It has a length scale on a slide , on which a cover slip is mounted. The length scale is usually 1 mm long and divided into 100 equal sections, so that one section corresponds to a length of 10 µm. There are also stage micrometers where 2mm is divided into 200 sections. The object micrometer is so named because it is placed on the object table instead of an object, the specimen on the microscope slide.

It is used to accurately determine the magnification of a microscope with a specific objective. For example, it can be used to precisely determine the distance between two scale lines in the ocular scale ( ocular micrometer ) of a micrometer eyepiece . This distance is called the **micrometer** value. If x intervals of the stage micrometer correspond exactly to z intervals of the eyepiece scale, the micrometer value can be calculated with the formula MW = (x • y) / z, where y is the interval length of the stage micrometer.

For digital cameras or their images, an object micrometer can be used to determine which distance in the object (for example 10 µm ) corresponds to how many image points ( pixels ).

Instead of an object micrometer, another object with precisely known size ratios can also be used for this purpose, for example a USAF 1951 test target .

## source

- Dieter Gerlach: The light microscope. An introduction to function, handling and special procedures for physicians and biologists . Georg Thieme Verlag, Stuttgart 1976, ISBN 3-13-530301-2 , p. 221-222 .

## See also

- Thread network ("reticle") in eyepieces for measuring or telescopes
- Crosshair eyepiece
- Circular micrometers in astronomy
- Reticle for marking in the weapon telescope image