Posted: Wed Oct 06, 2010 8:42 am Post subject: tamron SP 28-80 diaphragm problem |
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wupdigoj wrote:
Hello. I have recently bought this lens (quite cheap), and it had a strange problem: when you zoom from 80 to 28, the diaphragm closes about 3/4 point, and this without actuation the closing mechanism. So if you have the lens mounted on a camera and zoom to 28, the apertura will not be 3.5 any more, but something like 4.5. I could be live with it, but it will of course disturb the auto exposition in my pentax MZ-5. After disassembling the lens, I have reached the conclusion that the close down lever has not enought travel to take the diafragm from wide open to fully closed (at f32) so you have to make a choose. I have tried all sort of adjustements, and finally have left the iris working as it should for wider apertures, but now it only closes to about f11 at 28 mm and f16 at 80 mm. Not a big problem, but somehow disturbing when using aperture priority. Of course, if the camera "choose" f16, it will close only to f11 so overexposing.
Any clues??. TIA
Javier |