# B Optical instruments: Microscope and Telescope

1. Mar 13, 2016

### D. Wani

What are the different formulas for the calculation of magnifying power of a microscope and a telescope? And how would we use the sign conventions in them?

2. Mar 13, 2016

### drvrm

If the eye is relaxed for distant viewing, the telescope simply produces an
angular magnification equal to the ratio of the focal length of the objective to the focal length of the eyepiece,
so M.P. = - (fobjective / f eye piece) ( The negative sign indicates that the image is inverted.).

Magnifying power(M.P) of a microscope. = -(g /fobjective).{(25 cm)/feyepiece.} , where g is The tube length .
It is the distance between the secondary focal point of the objective and the primary focal point of the eyepiece.
25 cm. is the least distance of distinct vision of human eye.

3. Mar 13, 2016

### D. Wani

What is the difference between angular and linear magnification

4. Mar 14, 2016

### tech99

Perhaps I can illustrate this difference by using the two instruments to project their images onto a white screen. For instance, a telescope projecting the Sun's image on to a card and a microscope projecting an image of a cell on to a card. You will notice that the Sun's image is smaller than the actual object, but the cell's image is larger than the object. So the telescope does not make an image that is bigger than the original, but makes the eye think so by increasing the angles. I was taught to refer to "magnifying power" for telescopes, rather than magnification.