Reverse lens macro refers to turning your camera lens in the opposite direction against the camera body, creating a cheap but limited macro lens. I recently purchased a macro reverse ring on amazon for my Canon 7D and 50mm 1.8 lens. The macro reverse ring is made to attach to the front of the lens where you would usually attach a filter.

Key Points to Remember with Reverse Lens Macro –

1. The Macro Reverse Ring comes in different sizes depending on the size filter your lens takes. (The Canon 50mm 1.8 = 52mm)
2. There will be no auto focus when the lens is attached in reverse. The only way you can focus is by moving the camera body closer or further away from the subject.
3. You can not adjust he aperture when the lens is attached in reverse.

Overall reverse lens macro is a cheap but limited way to get into Macro Photography.