Tamron 35-80mm SP f2.8-3.8 01A

     I got lucky.   I actually found a decent copy of this lens.    It's a legendary lens, renowned for its macro performance and build quality.   I spent a few  minutes shooting snapshots with it on the T2i.    I was immediately impressed.   Focus and Zoom rings turn smoothly w/ medium resistance.   Focusing is as easy as it gets with a vintage lens on a d-slr.    It is very well built but not heavy.   It balances well on the T2i.  
     It's sharper than many prime lenses at all apertures and focal lengths.   It's not perfect, but it's pretty darn good.   
     It will fringe in harsh light up to f5.6.   That is its only weakness.   Flare is very well controlled.    Contrast remains excellent even in direct backlight.  

     Contrast is exceptional at all settings except 35mm f2.8.    
     Color rendition is superb.   

     Bokeh is generally pleasing for a zoom lens, but it can get a tad busy.    Bokeh fringing at 80 is quite noticeable wide open.   Stopping doan helps quite a bit.  The same is true at all focal lengths.  

     Black and white tonality is exceptional.    This is a great lens for street shots and architecture.
     I did not notice any vignetting on the T2i but I'm sure you will see some at 35mm f2.8 on full frame bodies.   Distortion is also negligible.

     While I can not compare this lens directly to a Contax Sonnar 35-70mm f3.4 or an Olympus 35-80mm f2.8 I can confidently say this is one of the best zooms I have ever used.  If you have an opportunity to acquire one, do it.