Figure 7 is a higher resolution close- up showing the finest detail at the object focal plane in the transition region where the loss in detail with higher f/numbers (smaller apertures) becomes evident. My own preference is to use an Abbe criterion value of final magnification equal to about 440X N.A. when depth of field is a key issue. The corresponding calculated f/numbers from this Abbe criterion are f/110, f/73, f/44, and f/24 for the 1X test patterns shown in Figure 7.  

click image to enlarge (194K) Figure 7

click image to enlarge (177K) Figure 8

The next experiment consisted of photographing a dried butterfly at 1/4X magnification using the Olympus 135 mm f/4 macro lens with a tripod mounted OM-4 camera and dual flash system shown in Figure 8. The tripod mounted camera was kept focused on the body of the insect while exposures were made at whole f-stop increments between f/16 and f/45 while using a cable release. The resulting test images in Figures 9-12 were first shown at Inter/Micro-84. Note that the depth of field increases with smaller apertures. The loss in fine detail for the f/32 and f/45 images is evident in the close-up montage of Figure 13.  My preference for the optimum aperture from study of these images is f/22 and in agreement with an Abbe criterion of 440 times N.A. This is the aperture I would choose for an 8X enlargement. I would use an aperture of f/45 for a 4X enlargement to obtain an optimum balance of depth of field and high resolution.

click image to enlarge (614) Figure 9

click image to enlarge (617) Figure 10

click image to enlarge (610) Figure 11

click image to enlarge (603) Figure 12

click image to enlarge (222K) Figure 13