Question

If the image is on the same side of the lens as the object the image distance is negative by convention

Magnifier

• Where is it located with respect to the lens and the object?

telescope

The key to understanding a telescope is to remember that the purpose is to gather light from distant objects. The image from the primary lens is magnified by a second lens to increase its size. Why should you use a longer focal length lens as the primary lens and then add other lenses as eyepieces.

Answer 1

In a Magnifying glass, the object is kept in between the focus and the lens of the convex lens and a magnified image is formed beyond the focus. So by sign convention we take the position of image as negative with respect to lens and object because it is left to both lens as well as object.

In a telescope M=F÷f. Where, M=magnification

F=focus of primary lens

f= focus of eyepiece

Since in a telescope we want to see the far away objects as magnified so magnification must be grater than 1. So in a telescope the focal length of primary lens is more than the eyepiece. In other words, for magnification focal length of primary lens must be more.

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