Why is the calibration factor for ocular micrometer specific each objective combination?

The calibration factor for an ocular micrometer is specific to each objective combination because the magnification of the objective and the size of the image formed by the ocular micrometer are both variable.

The magnification of an objective is typically fixed, and it is usually indicated on the side of the objective. The size of the image formed by the ocular micrometer, on the other hand, can be varied by changing the distance between the ocular micrometer and the eyepiece.

When the distance between the ocular micrometer and the eyepiece is increased, the size of the image formed by the ocular micrometer decreases. Conversely, when the distance between the ocular micrometer and the eyepiece is decreased, the size of the image formed by the ocular micrometer increases.

This means that the calibration factor for an ocular micrometer is specific to each objective combination because it takes into account both the magnification of the objective and the size of the image formed by the ocular micrometer.

For example, if an objective with a magnification of 10X is used with an ocular micrometer that has a calibration factor of 0.1 mm, then each division on the ocular micrometer will represent 0.1 mm in the actual specimen. However, if a different objective with a magnification of 20X is used, then each division on the ocular micrometer will represent 0.05 mm in the actual specimen.

Therefore, it is important to use the calibration factor that is specific to the objective combination that is being used in order to ensure accurate measurements.