<p>Hello Luther, <br /><br /> I've been meaning to open mine up because it is my understanding is that the bulb is rectangular, and that it will cover 5x7, barely, and I mean barely. Could you verify that for me? Aristo used to make an adaptor for a Durst 5x7 but those are impossible to find. I'm going to have to have something made so I can use the VCL 4500 on my Zone VI 5x7 enlarger because I shoot 5x7. Once I get it open, or someone else opens it, I'll post a picture of the location of the photocell.<br>
I had to change a bulb in a different 5x7 Aristo head, and I recall that the photocell goes in the middle, with the sensor facing away from the bulb, I believe. There are instructions in the manual for RHDesign's fStop timer for where to put a photocell.<br>
Louise Kessler at Voltarc (Louise.Kessler@voltarc.com) is a wonderful help and will sell you new bulbs for the VCL4500. She won't have the photocell though, just the bulbs. <br /><br /> Best, <br /><br /> Larry</p>