# How do I figure out magnification here?

1. Apr 29, 2016

### brinstar

1. The problem statement, all variables and given/known data
"Find the magnification of the following system: A diverging lens with focal point -9.5 cm is placed 4.35 cm to the right of a converging lens with its own focal point of 13.0 cm. Parallel light enters the converging lens from the left."

2. Relevant equations
M = -p/q
1/p + 1/q = 1/f
p of diverging lens = d - q of converging lens
Mtotal = M1 * M2

3. The attempt at a solution

So I figured out the magnification for the diverging lens and got 11.17647059. I cannot for the life of me figure out the magnification of the converging lens, and this is all because the object distance is infinite. How exactly do I get the total magnification (which is the product of my two magnifications) if the object distance for my converging lens is infinite? That would leave me at 13.0 cm divided by infinity....

2. Apr 29, 2016

### DarkMatter5

Magnification (of the whole telescope together)= fo/fe

fo is the focal length of the objective lens (converging)
fe is the focal length of the eyepiece lens (diverging)

The object distance doesn't matter.

3. Apr 29, 2016

### brinstar

Wow! >.< I feel so dumb.

Thanks so much for the reply!

For some reason, though, my teacher never gave me that formula in class. The ones I gave were all I had to work with. I didn't know you could get magnification without object distances and height!

4. Apr 29, 2016

### DarkMatter5

No problem . Now you know! Feel free to message me if you have any more telescope or astro questions.