Karl, As a follow-on comment on:
It may even take you a few hours to work out which aperture is sharpest on your lenses - assuming it's something you haven't already done..
I use ND material (neutral density, gray filter) in sheet form, between the light source and the negative, to adjust the intensity of the flash. You cut any size ND filter, and it was very inexpensive to purchase a large sheet. You can just keep adding layers and opening up the lens, until you get the aperture you want. It probably works better than trying to mount an ND filter on an enlarging lens. One can also change the number of sheets to compensate for the density of the negatives, and maintain the aperture. The Bowens illumitran slide duplicator has a knob that adjusts the flash intensity, and a system to meter the exposure, which also helps speed up the process. Since the Illumitran was built for ASA 50 or slower duplicating film the light intensity needs to be reduced to obtain the optimum aperture.
The manufacture or others may have already worked out the best aperture for the lens.
Steve H
