The microscope and some hints on how to use it / E. Leitz.

  • Ernst Leitz (Firm)
Date:
[1910]
Catalogue details

Licence: In copyright

Credit: The microscope and some hints on how to use it / E. Leitz. Source: Wellcome Collection.

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    a little distance from the e^^epiece. I'he bright circle is known as the pupil of fhe eyepiece or the Ihunsden disc. I'he plane at F is the posterior focal plane of the objective, and the plane at Fi is the anterior focal plane of the eyepiece. The distance of these two planes is described as the Optiecd luho- Jenyth = A Let fi be the focal length of the objective, f2 that of the eyepiece, then the resulting focal length of the entire microscope is ^ fi . f2 t = A The distance betw'een the plane Ti, wdiich is the upper edge of the tube and T, the shoulder of the objective collar, is known as the Mechanical Tiihe-lenyth. Let the pencil of parallel ra^^s which reaches the be pro- duced backwards, and at a distance of 250 mm from the line A let a line Q* P* he drawn at right angles to the axis of the nri- croscope, then the ratio _ .r 250 P Q f is a measure of the magnifying powder of the microscope, in that this ratio shows how many times the image of the object as seen in the microscope appears enlarged as compared with the object itself, supposing the latter to be viewed at a distance of 250 mm from a norm.al eye. In order that all rays wlaich proceed from the object to the objective may reach the retina of the eye the pupil of the latter should coincide with the exit pupil of the eyepiece, as shown in the diagram. To understand how the expression for the magnif3ung power Q* P* M = ' . has been arrived at we wall consider the case of an object viewed by a simple lens of a focal length P. It will be eas\' to show by reference to Fig. 3 that its magnifying power will be - * to