Summary: This lens is close enough to what I was looking for. I got it for a price you could not beat anywhere. A wide lens/zoom with no vignetting. I'm new to DSLRs and I own a 7D. This lens has some depth of field, which is intriguing for me since all the wide lenses I ever used were adapters for camcorders. Zooming with a wide lens is a treat. I had trouble focusing the lens outdoors.
Summary: My first impression of this lens was its weight. Wow. It's perhaps my heaviest lens in its class. At two pounds this is twice the compacted weight of a Tamron wide-angle zoom. It's almost too heavy to carry for long periods of time for photo shoots with the lighter-weight low-end Canon dSLRs. The heavy weight is less noticable with my Canon 7D.
Summary: I have a brand new canon 600d. There is a problem with the Tokina Auto Focus 16.5 -135mm f/3.5-5.6 AT-X DX Lens for Canon. It shows error message 01, clean contact on lense. The camera is fine with other lenses.