As an update to the presentation series on Macro Photography, this page adds information and tests on reversing rings, which are used to mount a lens backwards on the camera.
All modern lenses are of an asymmetrical design; that is, the front elements are not the same as the rear. These lenses are designed for best performance when the lens to subject distance is greater than the lens to image distance. This means that when a lens is used very close to the subject and farther from the image plane, it is not working in it designed corrected position. One solution is to reverse the lens on the camera. This is accomplished using an adapter ring with the camera mount on one side and filter threads on the other. These adapters are readily available and quite inexpensive compared to a dedicated macro lens or extension tubes. One example is shown in the accompanying photo below. I used a Bower Reverse Adapter AV52N from B&H, which cost about $12. Nikon has a very nice ring as well, but it costs $40. The rings come in various sizes to fit filter thread sizes. Step-up or step-down rings are also available to convert the reversing rings to fit other lenses.
The primary downside of these rings is the loss of all auto functions. Focus and exposure must be set manually and the lens has to be manually stopped down prior to exposing the image. Since the extreme magnification obtained by lens reversal means using a tripod, this is not that much of a burden in practice. Lenses that have an aperture ring work best for this. The Nikon G lenses do not have a convenient way to change the f stop when not mounted on the camera. Adapters are available for G lenses to allow aperture changing, but they tend to be expensive.
Because non-macro lenses are designed for imaging distances of one or so feet to infinity, the focus adjustment travel is relatively small. This means that reversed non-macro lenses have a very small reproduction ratio range. This can be overcome by using extension tubes or bellows along with the reversed lens.
Well, how did it work? Three lenses were tested, a Nikon 50mm f/1.8 prime, a Nikon 28mm f/2.8 prime, and a Nikon 18-55 zoom at two focal lengths. These are shown below. Note that the zoom setting are only approximate, as evidenced by the different magnifications. Click on an image for a full sized version.
As expected, the 50mm prime was sharpest, followed by the 28mm prime. The zoom was OK, but a bit soft, with some color fringing at the edges.
Reversing rings provide an inexpensive way to turn a prime normal or wide angle lens into a very acceptable macro tool, with the limitation of all-manual operation.