Quote Originally Posted by df cardwell
For getting the most from the lens you have,
lay a mirror on the edge of the print and stop down until you see a clear aperture. It may be a stop or stop and a half from wide open.

Go no further.
Neat trick with the mirror. I assume a clear aperture is when all leaves are showing. This is a different aperture depending on the magnification. Hence the range of 5.6 to 8 as proffered by Ralph and Claire. All these years I thought f11 to be the optimal due to my flawed logic. Thanks.