A previous review panning the 28-105 prompted me to run my own unscientific test leading to this partial review. I shot some flowers indoors under controlled lighting from a tripod with a canon 28-105 f/3.5-4.5, a Canon 85 f/1.8, and a quantaray 28-90 f/3.5-5.6 kit lens. I shot all at f/5.6 raw then used photoshop raw conversion with no adjustments and studied at the differences on a calibrated monitor: both 100% crops at the focus point which was right in the center of the field, and fit-to-screen views of the overall scene. Here's what I observed:
The 85 f/1.8 was significantly sharper than either of the zooms: in the center, with all lenses stopped down to f/5.6. The two zooms were comparably sharp at this setting.
The color that I obtained with the 85 and the 28-135 were not far off (albeit to my untrained eye). The quantaray produced a clearly more yellowish image. Checking the histograms showed the image taken with the quantaray/kit lens somewhat darker. I could really tell if the "yellowness" was really just darkness, but in any case, I judged the kit lens to produce an image that was poorer in color although not much in resolution from the 28-105.
To my surprise (somebody help me out here), the 85 produced a tighter zoom than either the 28-90 or the 28-105 max-zoomed. The 85 was noticeably tighter than the 105 at 105. Even the 28-90 was a little tighter at 90 than the 105 at 105. The 28-105 is a used lens that I bought used at FM, so I cannot be entirely sure of its provenance, history, etc. Cosmetically it's fine and it seems to work fine and do what one expects for such a zoom. It just seems to be more a 28-85 than a 28-105. Would someone be so kind as to tell me if I'm missing something obvious -- which is possible given that I'm new at this.