Question

A converging lens (f1 = 24.0 cm) is located 56.0 cm to the left of a diverging lens (f2 = -28.0 cm). An object is placed to the left of the converging lens, and the final image produced by the two-lens combination lies 19.7 cm to the left of the diverging lens.

How far is the object from the converging lens?

Answer 1

I have to be honest, when using the lens equations for multilens images, I nearly always mess up the signs. So what I do, is do a ray diagram of the first lens, then over sketch it with the image of the first lens becoming the object of the second lens, then eamining the final object. Of course, it is not accurate, and can't be used (my sketches are "engineering" sketches), but it then allow me to examine the results of the two lens equations to make certain it makes sense, and is right.