len10@ihuxw.UUCP (06/10/83)
I just discovered the solution to a photo problem and want to share it with you on the net. Problem: Pictures taken with my TAMRON zoom lens were consistently overexposed (about 1 f stop) except when the lens was stopped completely open (f 3.8) - this on an aperture priority Contax 139Q. Flash pictures using TTL flash metering were perfect. Solution: The lens had a slow-operating aperture which would not quite close down fast enough before the camera shutter would fire. Since the Contax only performs light readings off of the film plane during flash exposures, only flash pics came out well (unless the lens was set wide open at f 3.8 for available light shots). You can test for this on your own lenses (assuming you notice lots of over exposures) by looking through the lens from the back with the camera back open and film removed. At slow shutter speeds (1/2 to 1 second) you should see no aperture movement for whatever f stop is set during the exposure. Furthermore, setting the lens to each of its f stops should result in a noticably different aperture size when the shutter is released and the lens is viewed through the back. I hear this is a common problem for teleconverters. TAMRON fixed my lens very promptly, by the way. Len Dombrowski BTL - Naperville, ILL.