The Student Room Group

Lens magnification

I have a two lens problem. I have been given the focal lengths of two lenses and their separation. using matrix methods, I have calculated their combined focal length. the question now asks for the magnification. How do I calculate this?

I know that M(total) = M1 * M2 but I am unsure on how to calculate the individual magnifications. Possibly using M=-v/u but what is v and u?
Are these two lenses meant to be configured as a telescope or microscope? If so, the image distance is usually either set to infinity (telescope in normal adjustment) or 25cm - the so called near point.
The magnification clearly depends on the object and image positions.
well it doesnt say anything about the object distance which confused me. altho i have heard of the visual near point, altho its unmentioned in the problem
Original post by samueltaylor123
well it doesnt say anything about the object distance which confused me. altho i have heard of the visual near point, altho its unmentioned in the problem


What does it say? It would help if you gave more information.
Is it 2 thin lenses separated by a distance less than the focal length of the 1st lens?
Are they separated by a distance greater than the sum of their focal lengths.
What type of lens are they? Both convex?
Without this information I can only repeat my 1st suggestion, that you assume the image to be at either infinity or 25cm.
A huygens eyepiece consists of 2 thin lenses at focal lengths 20mm and 30mm separated by 25mm. calculate the focal length of the eyepiece (which i have done) and hence it's magnification.

Quick Reply

Latest