Tamron Adaptall to Pentax adapter problem

[pooschey]

I just got hold of a Tamron SP 90/2.5 and a SP 70-210/3.5 and the 90/2.5 came with a original Pentax Adaptall mount. However, when I mounted it to my Sony A700, it kept giving me a "Camera Error" message.

I took it out to examine against my Pancolar 50/1.8 and Sonnar 135/3.5 and realised that because both of these have a A/M switch, when the M is activated, the pin on the lens is unsprung.

Comparing it to the Adaptall mount, I found that the pin is always sprung. Examining the Adaptall mount, I find that the pin is pushed up by a curved spring that goes along the side of the mount. I've also did a search on 3rd party Tamron Adaptall to Pentax screw mount and found that these don't have a pin out.

It seems that the pin need to be unsprung in order to get it to work on my camera. Can someone care to share if this is how it should be and how do you go about keeping the spring on the mount down?

[ManualFocus-G]

Hi do mean you need to keep the pin pushed in? When I had my Sony a100 and a200, I just pushed a bit of paper inside the mount to keep the pin pushed up. I needed to do this in order to get the aperture to change.

[Minolfan]

For me the same. It is easy to push a little piece of plastic foam to push in the mount before mounting to the lens to keep the lens aperture on manual.