I had an old vivitar autofocus 2X Tele converter in film days. As the digital era started it turned out that these converters can generate worst kind of image, so it went out of service. But why not through away the inner glass element of this converter and turn it into an extension tube. So I removed all the glass component and covered the shiny aspects with black felt found in the opening of good old film canister. Now I have a fully functional AF Extension Tube. Which works perfectly with my Nikons. And it's solid too. I have been using it for a long time and it has become a permanent part of my macro setup.

The standard tool of macro photography is a Macro lens. But a lot of us can't afford a dedicated macro lens due to high expense. A reversing ring is an easy solution. But the major disadvantage of using a reversing ring is that, you have no control on aperture. You have to set the aperture manually or use third party device to make it work. And in macro photography a hair movement of the lens while setting the aperture can make the image out of focus.