Any way to get a specified magnification effect? I'm trying to simulate the magnification of a rifle scope. However, I don't want it to be a random amount, as rifle scopes typically have a set range of magnification (for example anywhere from 6x to 14x).
I've done research prior to posting this, and I know having two UV Spheres scaled down from their poles and at different overall sizes would generate the effect I'm looking for, but is there a way to get a specified setting say like 4x zoom? I'm not looking to get a range to adjust from, just one level of magnification.

Also, if it helps, I'd preferably like to do this in the Cycles rendering engine if at all possible.

I made a rough model of the ACOG 4x rifle scope and studied up on the internal parts. It contains two eyepiece lenses, a roof prism and the objective lens, which I modeled. It works somewhat, most likely because I made the prism too square.
I would recommend not trying to actually model the lenses to magnify the image, but rather place a camera in front of the scope with a higher Focal Length.

Then in the compositer you can add the scope's camera view to the final image.