Wide-angle distortion isn't an issue when the lens is reversed. Try reversing your 28mm and look through it. You'll find that the magnification you're getting is way more than "pretty much close up". As Keith stated, a set of extension tubes will get you to that range. I have a Vivitar macro-focusing teleconverter that lets me do basically the same thing that extension tubes will. That's another option, by the way. The Vivitar 7-element macro-focusing teleconverter works quite well, even with a regular old 50/1.8. And you can vary the magnification all the way down to 1:1. Not available new anymore, but they do show up on eBay from time to time. But if you want to do high magnification photography, then reversing lenses is an economical way to achieve this feat.

Best,

Michael