Originally Posted by gofour3 
Reversing a K50/4 Macro will give you higher magnification, due to the deeply recessed front lens element. Reversing acts like an extension tube in this case and image quality is also improved when magnification is greater than 1.0x.
When reversing a lens, the more wide angle the lens, the more magnification you have. I have reversed a 24mm and ended up with over 3:1 magnification.
http://www.pentaxforums.com/forums/p...ngle-lens.html