A COUPLING RING joins two lenses together by their filter threads. If you fit a telephoto lens to the camera and reverse mount a standard or wide angle lens via their filter threads, you produce a multi-element high magnification lens. This can also work for cameras and camcorders with fixed zoom lenses. Set the lens to maximum telephoto and then mount another lens with a shorter focal length in reverse in front of it.

 

HOW DOES IT WORK ? By mounting one lens onto another, you are producing a multi-element macro lens whose magnification is the ratio of the focal lengths. If you mount a 200mm lens on the camera, and reverse mount a 50mm lens via the filter threads, you get a magnification of 4:1. If you reverse a 28mm lens, you would get about 7:1. Two lenses of the same focal length would give 1:1.   HOW DO I USE IT ? Fit the longest focal length lens to the camera. Couple the shorter focal length using the filter threads. Make sure the diaphragm of the reversed lens is set to fully open. Depending on the focal length of the telephoto lens, the field may be restricted by the open diaphragm in the reversed lens, and you may need to crop the result. Rough focus on the subject by moving in and out of the subject, and fine focus using the focus ring of the telephoto lens. The focus ring of the reversed lens will have no effect. All exposure modes for the camera/lens will be available. On-camera flash will probably not be very effective as it will ‘miss’ the subject. An alternative lighting set up may be necessary.   HOW CAN I TEST THE EFFECT BEFORE I BUY ? Mount a long lens on you camera, and hold another lens against it so that their filter threads are together. Point the combination close to a sheet of newspaper. Count the words/letters to determine the field of view. Try different combinations of lenses.   ADVANTAGES Small accessory that fits in the pocket for very close work. Full auto functions retained. DISADVANTAGES Possible circular image due to diaphragm in reversed lens acting as a field stop. Result may need to be cropped.   The shots below (of a standard playing card)  were obtained by mounting a 55-200mm zoom lens on the camera and setting it to the 200mm end. An 18-55mm lens was reversed on the front.        18mm focal length lens - closest focus       200mm focal length lens - closest focus         18mm lens reversed onto 200mm lens        35mm lens reversed onto 200mm lens      55mm lens reversed onto 200mm lens               giving approx 11:1                                            giving approx 6:1                                   giving approx 4:1