Just ran across a problem that is puzzling to me. A flash extender, which is basically Fresnel lens, of which several brands are marketed, does not produce results on my D100. It used to work on a film Nikon camera, now it makes the images actually darker, rather than lighter. Has anyone experienced, and/or solved this issue? Many Thanks.
I recently used a flash extender with my SB80 and D1X on an African safari and had excellent results "throwing" the flash 100 feet or more (ISO 400, 80-400VR wide open) I took care not to put pressure on the button that changes the coverage to 14mm I manually adjusted the focal length on the flash to 50mm which is what the flash extender recommends.
My problem was that it was difficult to attach the flash extender in a hurry and I missed out on a great leopard shot while I fumbled around in the semi dark trying to get the flash extender gizmo and the rubber band attachments fixed on to the flash
Mmmm. SB26? I don't think that baby supports D-TTL? In which case, you were using the flash's auto function. My guess is that the extender lit up (they are translucent-white, after all) and so dumped a whole lot of light on the the sensor which is on the flash. So, the flash decided "good exposure" & turned off. If you had a big extender, it could even have blocked the flash's sensor from "seeing" the subject?
These are just guesses - but I am suspiscious about the flash compatibility.
Interesting theory, and it's probably something closely akin to what you describe. However, the sensor is on the front of the flash, and the light reflected by the fresnel lens on the extender just bounces back to the flash itself. No way it can reach the sensor on the front of the flash. I have however, placed my SB26 for sale and ordered an SB-80DX. That to have TTL, and fewer test shots.