Contax AX depth field button doesn't work on a 50mm planar

[emmanuel_b1]

<p>Hi there, I'm facing with a "problem". I own a AX body with the distagon 2.8 35mm and the planar 1.7 50mm No problem to test the depth field (is it correct?) with the 35mm , but button doesn't work with the 50mm. After analysis , I found a small moving index on the body (5 o'clock facing it) which is avoiding the button action on the 50mm and not on the 35mm. What is the use of this index?<br>

<img src="http://membres.multimania.fr/ebgy/tempo/contax/contax_index.jpg" alt="" /></p>

[sumo_kun]

<p>I don't know what it does exactly as I don't have my camera with me at the moment but I think it tells the body what aperture the lens is at? Anyway the AX doesn't do DOF previw in Tv or P modes so try in Av mode. Also does the tab move when you change the aperture?</p>