Mt Spokane Photography said:
When you get really close, there is almost no depth of field, at f/1.2 you'd likely just have a blur. Macro users find that even very small apertures are marginal.
+1
You'll want to stop down, with high mag even f/11 or narrower is very thin DoF. But you did say 'experiment', so try f/1.2...
Regarding extension tubes vs. close up lenses, both have pluses and minuses. Both cost IQ, tubes and good CU lenses (like Canon's double element 500D and 250D) are similar, cheap CU lenses are worse. Tubes cost you some light, CU lenses don't. Tubes fit any lens, CU lenses are sized for filter threads (you can use step up rings).
The biggest difference is the lenses where each is effective. Tubes give increased mag inversely proportional to focal length (shorter FL means more mag increase), whereas CU lenses increase mag (in part) based on a direct proportion to FL (and in part based on the lens' minimum focus distance). As a general rule of thumb, shorter than 70mm you want a tube, 70-100mm either will do, and longer than 100mm you want a CU lens (assuming your goal is higher mag - I use a 25mm tube with my 600/4 to get a closer MFD, 12' vs the native 15').
With a 50mm lens, tubes are the way to go. A 500D can actually
reduce the max magnification of a 50mm lens instead of increasing it.