Lenses: If given object height and focal length, is it possible to calculate...

Byrne

the image's height? If so, how? I have the formulas, but see no way of making a substitution.

If you wanted to know the problem, it states:

The focal length of a camera is 35 mm and the radius of the moon is 1.74 x 10⁶ m. Calculate the diameter of the moon's image that appears on the camera's film.

jtbell

It's impossible to solve the problem using only the given information. However, if you look up the distance between the earth and the moon from somewhere...

HallsofIvy

Take the moon's distance from the earth to be infinite.

Doc Al

For the purpose of calculating the image distance from the lens, the distance to the moon can be considered infinite. But not for the purpose of calculating the image size on the film.

Paul Wilson

For the distance between the Moon and Earth, see this page. http://www.freemars.org/jeff/planets/Luna/Luna.htm