To begin with, I have to admit that I'm not qualified to test lenses. I don't shoot charts or brick walls. But the results I got from this lens surprised and excited me, and I thought to share them with you. These are just preliminary observations and updates may be added as I get the chance to try the lens in varied situations in real life.
The photo tests were controlled as best as I could. Turns out that this super-zoom isn't a bad performer after all. I got this lens second-hand just yesterday night, and it's in mint condition, as far as I can tell. Initially I wanted to jump straight for the 24-105mm f/4L during the revamp of my lens setup. But when this one popped up, I couldn't resist the urge to try it. The 28-300mmL is quite rare on the local market, and seemingly quite unloved.
It closely resembles the 100-400mm f/4.5-5.6L functionally, in the sense that both of them are push-pull zooms. The 28-300mm is even weightier, perhaps feels a little better built and operates just as smoothly. But because the angle of view changes so much throughout the zoom, getting the 'right' framing does take a degree of control.
Here are some 100% crops taken indoors, using a 1D, remote release, mirror lockup, and a naked lens (ie. no filter) with IS off. In some pictures, moire may be visible and this is courtesy of the 1D's sensor. Photos shot in RAW. Converted with DPP. Neutral picture style, sharpness +2. In all cases, only the center focusing point was used, and this was centered over the 'T' in the word 'Centrum'.
28mm @ wide open aperture
28mm @ f/8
50mm @ wide open aperture
50mm @ f/8
105mm @ wide open aperture
300mm samples coming up next...