Combining Two Lenses for Shooting Extreme Macro Images
For starters you need two lenses
The first one mounted on your camera normally. The second lens mounted in reverse to the first lens by using a reversing ring.
Reversing rings are simply adapters featuring a real lens mount on one side plus male filter threads on the reverse side. Your second lens is then attached to your new reversing ring using it's filter mount. Most lenses are engineered to deliver optimum results when the lens-to-sensor distance is less than your lens-to-the-subject distance, so by using an ordinary length lens for macro shooting, it could produce better results when it's reversed.
If you happen to have some sort of telephoto lens plus a 50mm lens in your camera bag you just might want to try this idea. It's pretty simple, really probably won't take more than a couple of minutes to read. All that's needed is a reversing ring (coupler), and maybe a filter step up ring, plus a piece of folded paper or cardboard. For less than $20 dollars you can have an extreme macro setup! Having a zoom lens is not entirely necessary although focusing in on your intended subject becomes much easier than using two prime lenses. You can also adjust your subject's magnification by using a zoom.
The lenses I've used are an inexpensive Sigma 70-300mm with a Nikon 50mm f/1.8. Each filter thread size on each lens will determine the adapter size that you'll need. I used a 52mm to 58mm coupler to attach the two lenses.
The next step is to simply attach a ring to a corresponding lens. Now just combine both lenses into one macro setup by using the rings: Should appear somewhat like this:
Reversed Lens Macro Setup
MOST IMPORTANT. You'll need the aperture setting on your 50mm (or the lens you're using) full open. If your lens has no aperture dial This is where you wedge the aperture slide open using the folded paper or cardboard. I like to used notepad paper folded over just enough to wedge the aperture open with a snug fit. Use whatever works the best for you however it's difficult to damage a lens when using this approach.
52-58mm Reversing Ring
Keep in mind that using setup similar to the one I have described above, with the 70-300 set at full zoom which will give you a magnification of 6:1, 6 times it's actual size (300mm with the zoom divided by 50mm with the prime lens). For smaller magnification simply adjust the zoom. By zooming to 200mm the magnification will become 4:1 - zooming to 100mm will become 2:1 etc. One more important thing to keep in mind is that by using less zoom , you'll have more vignetting. Using full zoom there will hardly be any vignetting.