Tamron SP 28-80 barrel action

[SkedAddled]

I've just received a copy of this lens today.
It's cosmetically very nice, and optically near-mint. I think I'm going to enjoy this lens, if we ever get back to some fairer weather.

But this lens has an unusual issue:
With focus @ infinity, I can turn the zoom ring to the 28mm setting. When it's set at 28mm, however, the focus barrel then only turns to around the 3-ft/0.9m mark on the scale. It appears that the obstruction is cleared when the zoom barrel is turned to around 30mm on the scale.
Conversely, if focus is turned closer than 3-ft, the zoom barrel hits something at the (approximate)30mm mark. If I hold the lens just so, turning the barrels at the same time, I can feel the obstruction let up very suddenly.

Has anyone else encountered this, and can anything be done about it without dismantling portions which would affect infinity focus?

The rear Adaptall mount may have been dismantled before, as the 3 phillips screw-heads look to have been manipulated with a less than firm hand. The screws were also extremely tight, much tighter than the SP 60-300 I received. I removed the rearmost mount in an effort to see if there was anything obvious, but my efforts were completely inconclusive. The rest of the lens appears to be undisturbed, though I can not be certain.

[Xpres]

I think it's meant to be like that - close focus is just not as close at 80 than as it is at 28. Mine's the same anyway.

[Farside]

This makes it three, so it's normal for this lens.
The SP 35-80 is the same - close focus requires a longer zoom setting. In fact, it makes you do it; as you turn the close focus, it zooms in.

[nemesis101]

Mine too!

This is the mechanism / means by which Tamron accomplished its 'continuous or constant' 'CF' focus... so that one can go from wide - tele and standard - macro seamlessly...

Doug

[SkedAddled]

Many thanks for the feedback. With at least 3 others like this, it's probably a sure thing that it's of the lens design. My only other Tamron, a SP 60-300, exhibits nothing like this, so I was a bit confuzzled at first.