Graybeard,
Indeed it should be more efficient as the condensers focus the light onto the negative.
Also ensure you align / focus the bulb. The Durst has an elegant system to correctly position the bulb for ultimate focus based upon the condensers used and lens focal length.
There is a good article on the Durst USA site (Jensen Optical) on design and use of condenser systems: http://www.durst-pro-usa.com/world_images/artcon.htm
Hope that helps,
Len
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