A simple optical test

A method for comparing macro lenses at home
 
A time ago I decided to test the results that could be achieved in closeup photography by using enlarger lenses. I was interested in comparing them to the Micro-Nikkor 105/2,8 AFD in the region of reproduction ratios beyond 1x where the latter does not really work at its best. Thus, I set up an optical bench using my tripod, vertically-mounted camera and a PB-6 bellows so that I could test several reproduction ratios for each lens.

As someone lended me a Nikkor EL 50/2,8 enlarging lens, I only needed a test target. It should be some professional one, like the used for lens resolution testing, but they were not available to me at that time; and additionally, they are not intended for macro tests. So I built it myself with scaled paper and a post stamp. Calibrated paper (1 mm. interval) allows to precisely calculate the exact reproduction ratio. As the stamp is engraved it gives a good field to test for sharpness (see below). I included sticky notes in each photo to record the theoretical f-stop. Of course I also recorded the extension and type of lens for each shot.
All pictures were taken with 2 flashes aimed at 45 degrees and on negative low-grain film. Maximum care was taken to ensure that the focusing plane and the target were parallel. Given that I was just comparing, it was not necessary to use a real high-resolution film. All combinations of extension and main f-stops were tested for the two lenses, getting beyond 4,4x in both cases. The maximum enlargement degree can be checked at left (whole negative; following your screen resolution, of course, you may see it larger or smaller).
The results of such tests can be analyzed on the negative or even on commercial enlargements (considering that examining colour negative with a loupe is a real hassle). Actually, loss of quality due to enlargement is not relevant here as we only wanted a comparison, not absolute values. Should you have a film scanner, comparison could even be made on scans of tiny sections enlarged and examined onscreen. A sample is given below, corresponding to the Micro-Nikkor 105/2,8 AFD in both cases, near to 2,2x reproduction ratio; the only difference being the f-stop, as the first was shot at f/16, whereas the second one was taken at full aperture.
 
Results were interesting as both lenses performed equally well. In some cases the Micro-Nikkor was even better than the enlarging lens, in reproduction ratios that were not optimal by design. Generally speaking, I got somewhat deceived by the enlarging lens so I actually sent it back to the store. However, I discussed later with other photographers; who advised to reverse the enlarging lens (that was asymmetrical), to get its optimum performance in "natural" position (subject in place of film plane). So years later I have tested again such a lens (even nicer this time: a Rodenstock Apo-Rodagon 50/2,8) in reversed position, with much better results.