The eyepiece of a refracting telescope (see Fig. 34.53) has...

The eyepiece of a refracting telescope (see Fig. 34.53$)$ has a focal length of 9.00 $\mathrm{cm} .$ The distance between objective and eyepiece is $1.80 \mathrm{m},$ and the final image is at infinity. What is the angular magnification of the telescope?

Key Concepts

Image at Infinity

An image at infinity means that the final image formed by the telescope is made of parallel rays, which is ideal for relaxed vision because the eye is focused at infinity. Telescopes are often adjusted so that a distant object’s image is at infinity, ensuring that the diverging or converging rays exiting the eyepiece are parallel.

Focal Length

Focal length is the distance from the lens at which parallel rays of light converge to a point. In telescopes, both the objective and eyepiece have focal lengths that determine the image formation and the overall magnification. The objective’s focal length controls the initial image formation, while the eyepiece’s focal length is critical for magnifying that image.

Angular Magnification

Angular magnification is a measure of how much larger an optical instrument appears to make an object. In telescopes, it is defined as the ratio of the angle subtended by the image when viewed through the instrument to the angle subtended when viewed directly, often given by the ratio of the focal lengths of the objective and the eyepiece.

Refracting Telescope

A refracting telescope uses lenses to form an image of distant objects. The basic design includes an objective lens that collects light and creates an image, and an eyepiece lens that magnifies this image for the viewer. This configuration is central to understanding how images are formed and enhanced in such instruments.

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