Calculating Telescope Length: Refracting Telescopes

[edoarad]

in a refracting telescope, the lens's diameter is 1.02 m and its focal length is 19.4 m.
how long must the telescope be to get an image, 40 times bigger?

i would also like to get a link to a site explaining this kind of elementary optics.

 

[edoarad]

just saw the warning, please don't delete my posts :S they are in a close enough format i think..

 

[nlightner]

I can provide a response to the question about calculating the length of a refracting telescope. To determine the length of the telescope, we need to use the formula for magnification, which is given as M = f/fe, where M is the magnification, f is the focal length of the lens, and fe is the effective focal length of the telescope. To achieve a magnification of 40 times, we can rearrange the formula to solve for fe, which gives us fe = f/M. Plugging in the values given in the question, we get fe = 19.4 m / 40 = 0.485 m.

This means that the effective focal length of the telescope should be 0.485 m. To determine the length of the telescope, we need to add the focal length of the lens (19.4 m) to the effective focal length of the telescope (0.485 m), which gives us a total length of 19.885 m. Therefore, the telescope must be at least 19.885 m long to achieve an image that is 40 times bigger.

For further information on elementary optics, I recommend checking out this website from the University of Colorado Boulder: https://phet.colorado.edu/sims/html/geometric-optics/latest/geometric-optics_en.html. It provides interactive simulations and explanations on topics such as lenses, mirrors, and telescopes.