In article <4jsl3s$d7k@nntp4.u.washington.edu>, zeming@u.washington.edu says...

>I know that the later Sigma 21-35/3.5-4.2 (the one
>with the fixed hood) is an excllent lens.

The one I tried was definitely not excellent, being only
barely acceptable at the edges even stopped down (I think
it was the later version).

>As to the Vivitar series I 90/2.5 macro, the one I saw
>obviously is very old and ugly too. It has a built-in
>tripod mount. Is this lens the generally praised
>Vivitar SI 90/2.5 macro? or there are actually two
>generations? (make it three including the current
>Vivitar SI 90 macro lens). In that case, any one
>knows how good is the earlier one?

The 1:1 adapter for it has a tripod socket - is
that what you mean? I think there was only one
90mm version, the current one being a 105mm.
The 90 was very sharp, a tad lower in contrast than
Nikkors, and VERY prone to flare at normal focus
distances - which makes it unuseable for me much of
the time as a normal short tele, though for flash
insect shooting, it works very well by itself, with
tubes, with the 1:1 adapter, with the Nikkor 6T achromat,
with 1.4X and 2X converters, and with combinations of
the above. In other words, it is an excellent macro lens,
and an excellent basis for a very versatile and high
quality macro system.
Hope This Helps