I think there was probably a design change. I don't think it is wear.
I've actually at the moment got a 300/2.8 and two 400/4 Tamrons. What I
remember is that tightening the screw doesn't change the feel of the
detent. It locks a rotating ring in place which determines the focal
setting where the detent occurs - the lens focus tube rotates freely
with just the little snap of the detent as you go through it. I believe
all three of my lenses have a brass screw, with varying amounts of black
paint. My lenses are all olive drab.
Since your screw adjusts how pronounced the detent is, I'm pretty
certain it works differently than the three I have. I tried locking two
of them so that they wouldn't go beyond the detent and couldn't. I
believe production of the 400/4's stopped about 12 years ago. I don't
know if any of the 300/2.8s came with a canvas bag. My best 400/4 came
with a bag but not a black vinyl suitcase. I suspect the bag was a more
recent design. Probably cheaper but more useful for me. My 300/2.8 has
the black suitcase.
SN of 300/2.8 900xxx
SN of 400/4 803xx
SN of 400/4 807xx
Which is really surprising since my 300 has a higher SN than yours. I've
never thought of mine as being particularly new.
I've put the original yabe pages at
http://www.jeff-keller.com/tamron/Tamron 300mm f2_8.htm
http://www.jeff-keller.com/tamron/Tamron SP 400mm F4 LD-IF EX+.htm
Both contain at least one picture showing the ring with the screw that
locks the detent in position. Sorry about all the spaces in the URL.
That was how I saved it originally.
-jeff
I thought the white one was the earlier non-internal focus model. I
think the newer lenses have a black crinkle finish paint ... I've proven
my memory is less than perfect already though.
----- Original Message -----
From: "Walt Wayman" <hiwayman@xxxxxxxxx>
>
> More on the 300/2.8 Tamron and the little knob:
>
>
> As for the detent, on my lens it is quite pronounced, unmistakable
> except in instances of great haste or excitement. Just how strong
> it is depends on how much you tighten the knob, even to the point
> of having the full stop I described that allows focusing closer,
> but not farther.
>
> My guess is that the difference we're seeing in the way this
> mechanism works on different lenses has more to do with wear and
> tear than with a change Tamron made in the lens. The serial
> number of mine is 8217xx, if that will provide any clue as to
> provenance.
>
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