> Difference between f2.5 and f3.5 is significant - you will > appreciate it in low light levels!
...except that the Takumar Bayonet 135/"2.5", with its not overly generous 52mm filter threads (unlike the K 135/2.5, which has 58mm threads) would seem unlikely to be much faster than f/2.8. In any event, by my measurements, the Takumar Bayonet certainly has a much narrower front element than does the SMC K 135/2.5 - SMC K 135/2.5 : measured 52 mm front element diameter -> f/2.6 Takumar Bayonet 135/2.5 : meas. 49 mm front element diam. -> f/2.8 http://www.cetussoft.com/pentax/135's/135252.jpg The above is a photo of two supposedly f/2.5 135mm lenses - the SMC K 135/2.5 is on the left, while the Takumar Bayonet 135/"2.5" - the one that shows my reflection (<g>) - is on the right. It would seem that both lenses do not fit the same specification. Of course, the original point I quoted from is still basically true - there is still a significant difference between an f/2.8 lens and an f/3.5 lens. Fred
