APPENDIX E

A Macro Lens with Attachments

The working distances and magnifications were measured for a Sigma 105 mm macro lens with various combinations of extension tubes, diopters, and a tele-extender. The results are plotted as magnification versus working distance in Figure E.1. For each combination, measurements were made at far focus (infinity) and closest focus. The results are indicated with dots connected by red dotted lines. The points on the connecting lines have no significance and only serve to connect the end points. Each line is labeled to show the presence or absence of extension tubes (12 mm to 68 mm), diopters, and a Kenko 1.4x teleconverter. The red star shows the bare lens at close focus. Unconnected dots also refer to close focus.

The results show that a teleconverter in combination with extension tubes gives high magnification and large working distances. In each case, the extension tube was attached to the lens first. In other words the teleconverter was mounted directly on the camera body. The reversed 50 mm lens (20 diopter) gives high magnification, but at the cost of working distance. In Table E.1 I show the measured distances (see Figure 12.3) and the associated magnifications for all the combinations of the macro lens and attachments.

FIGURE E.1. Characterization of a 105mm macro lens.