In article <5a0qik$t6h@fidoii.cc.lehigh.edu>, ob00@CS1.CC.Lehigh.EDU says...

>How do I focus if I attach a lens onto another by using lens reversal adoptor?
>Lets say I attached a 50mm lens onto 100mm lens by using lens reversal adoptor >to get 2x magnification.

The focus ring of the lens attached will cover a very short range of focus
(a macro will cover more), but the main way of focusing that rig is by
moving the camera/lenses relative to the subject.
Hope This Helps