SN>> Even still, the entrance SN>> pupil on mine looks like about 51mm, which would make it f/2.6 or SN>> f/2.7.
> Same conclusion here. Yes. The Takumar Bayonet 135/"2.5", with its meager 52mm filter thread (unlike the K 135/2.5, which has a 58mm thread) would seem to be unlikely to be much faster than f/2.8. http://www.cetussoft.com/pentax/135252.jpg [The SMC K 135/2.5 is on the left, while the Takumar Bayonet 135/"2.5" is on the right.] Fred
