you can make a reversing ring out of a body cap and stepup/down ring. with a 50mm you'll get better than 1:1... the problem tho is that working distance from the front of the lens is about 12mm to subject. also you need a very small aperture opening for the DOF required. at f16 , it's awfully dark in the VF. i have gotten some great results but definately like a macro lens better or even extension tubes. 50mm of ETs on a 50mm lens = 1:1. also with a reversed lens you are putting the soft lens coatings of the rear element in harms way. i've done macros in every way devised except with a bellows and find nothing beats a dedicated lens for the job.
here's a reversed 50mm shot, full frame.