# Distance from the object to objective lens and focal length

## Homework Statement

1) The medium-power objective lens in a laboratory microscope has a focal length fobjective = 3.70mm . If this lens produces a lateral magnification of -42.5, what is its "working distance"; that is, what is the distance from the object to the objective lens?
2)
What is the focal length of an eyepiece lens that will provide an overall magnification of -130? Assume student's near-point distance is N = 25 cm

m=-di/fobjective

## The Attempt at a Solution

I tried using that formula to solve for this distance for object but it doesn't work out. I got that formula from a book where they assume that do is approx to be fobjective. Tbh, I don't quite understand how to get this "working distance". Anyone can help?

## Answers and Replies

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Matternot
Gold Member
Have you drawn a ray diagram? It should help you understand how "m=-di/fobjective" can be derived and thus, help you understand the question.