David storm over on the other forum noticed that my macro shots were looking odd compared to what they should considering I said they were shot at f32. He had the sigma 105 and ext tubes before and knew that the tubes hold the lens wide open regardless of it being set to f32. Question is can they be modified to allow A setting which eliminates the problem or do I need new tubes. Mine are a set of vivatar auto, (???) Any thoughts or anyone with tubes with contacts for sale ?
dpmiller wrote:are they A tubes and can you see what the aperture lever is doing, if lens and tube are off the camera?
Hi, the tubes have no contacts. When the lens is attached to tubes only, the aperture on the lens stays where set with aperture ring. As soon as tubes are mounted on the camera, aperture changes to wide open. Derek
The aperture is supposed to change to wide open, it only stops down when taking the shot, or give a DOF preview, or green button metering. Framing wide open gives shallower DOF for pinpointing focus & allows you to see a brighter image. Use either DOF preview or the green button to ensure it's shutting down when it should.
Hi Mike, thanks for the suggestion, but whether shooting at f2.8 or f32 in manual mode, and having changed nothing else, the exposure remains the same. It only shoots wide open. New tubes are on the way so I should be sorted. Cheers Derek