Hi,
i recently acquired an SMC Pentax-A 35-105 mm. It seems in very good condition, no dust marks, focus and zoom rings are rather smooth, no signs of heavy misuse or damage. It seems to take farirly good pictures as far as i can tell, as it is the only copy of this lens i've ever owned.
By visual inspection, i noticed a strange behavior of the diaphragm blades, and i was wondering if it is normal or not. I attached some pictures to explain what i believe i'm seeing, forgive me for the awful quality as they were taken with my cell phone.
The first one is a picture taken through the front of the lens, wide open (manually setting the aperture ring at f/3.5) and zooming at about 50mm focal length. I see a perfectly circular shape as i expect.
However as the focal length decreases towards 35mm (second attachment), i start to see some asymmetry, as if the iris blades do not completely retract out of the optical path when fully open, as they are supposed to be. In the third picture it appears that they are actually protruding out more than i would expect. This behavior does not change if i set the lens to A mode ( or any other setting) and manually operate the aperture control lever to open the diaphragm.
My questions are: Is it normal behavior ? Does this suggest a mechanical malfunction of the aperture mechanism ? I note that apart from that the aperture ring seems to operate smoothly and there are no signs of grease or stuck blades.
Thanks in advance for the help.
Last edited by simon_199; 09-04-2015 at 01:23 AM.