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# Lens magnification Watch

1. 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?
2. 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.
3. 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
4. (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.
5. 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.

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