I'm wanting to shoot macro using 2 lenses as described various places. My lenses are a 50mm, 30mm and a 75-300mm. lense sizes are 49mm, 62mm and 55mm. I did think Id just use the 50 and 75-300, but my 30mm is a superior lense. So thought might be better to use 30mm, but will buy rings for both. So thinking of buying reverse coupler of 55-58mm, and step up/ step down rings to fit into the 58mm. I'm not sure whether other rings are step up or down. Do I need a 49-58 step up and a 62-58 step down? And is this worth doing?
The longer the focal length, the less magnification on a reverse macro.
Personally I'd recommend you use extension tubes- from aliexpress- they're cheap enough and don't leave your rear element hanging out there.
The 50mm is the 'standard', the 30mm will give you 2x easily I believe, and after that it gets a bit unwieldy. Don't use the 75-300.