Tamron SP 28-135mm f4-4.5 28A

     The 28A is a push-pull zoom and part of Tamron's Adaptall SP lineup.  It is well made and heavy.   Filter size is 67mm.  It has a variable aperture range of f4 - f32.   At 135mm it is an f4.5.  The aperture clicks at half stops from f4 thru f16 then full stops until f32. It has an AE setting at f32 for automatic exposure camera bodies but the aperture ring does not look.  It has a 1:4 macro mode that will engage at any focal length by pressing a button and turning the scale ring.  This is a bit awkward as it will tend to activate accidently on occasion.  My copy does exhibit zoom creep which is undoubtedly do to the weight of the front section.    Focus throw is very short at about 1/5 of a turn.  Focus dampening is superb.  Zoopom dampening is typical of push-pulls.  It is smooth but hesitates in places.   New grease fixes that issue if it becomes awkward.  As of today I have not been able to do significant, optical testing of this lens.  I can say that it can be difficult to hold steady at 135mm because of its weight. It can be difficult to focus at telephoto lengths because of it's short focus throw.   If you have eye glasses, wear them.   Cameras with focus peeking will offer a great advantage when using this lens.  Optically, it is excellent by reputation and I can confirm that from my first impressions.