In article <6h0t3d$kco$1@agate.berkeley.edu>, rfung@uclink.berkeley.edu says...

>Does anyone in this NG have any experiences with the Vivitar series 1 28-90mm
>f/2.8 to 3.5 lense? Please email me back at rfung@uclink4.berkeley.edu with
>your comments.

The one I tried was a mediocre lens at best, having poor edge/corner
sharpness (even stopped down to middle apertures) and severe illumination roll-off. If you find one very cheap, it is an OK starter lens, but I
wouldn't get serious with it (if the one I saw was representative).
Any 50mm is generally faster/smaller/lighter/sharper than even good
mid-range zooms, which the Vivitar wasn't...
David Ruether
http://www.fcinet.com/ruether