I have compared the 28-135 directly to the Canon 24-105 / 4 L USM. At first I was convinced that there would be immediately visible benefits for the more expensive lens. But it was not so. My test setup: wide angle 28mm with Bl.4 and Bl.8 and 105mm with Bl.4 (5.6 at 28-135) and 8. I have in good light just added more detailed objects, imports the photos into Lightroom, by reworked best knowledge and then compared. To make it short: In the open aperture 100mm Bl.4 acts at 24-105 in the border area significantly fuzzier than the 5.6 of 29-135 (yes, there are not the same aperture values ...). The detail reproduction in the middle of the screen is so identical that several people could not tell which lens they find their way. In wide angle it looked the same: In the same panel, you can find almost no differences. Add to this that the 24-105 clearly visible color fringes generated in the peripheral areas, which has the 28-135 as well, but at half the purchase price. At aperture 8 the results looked so alike that I could not detect any significant difference here. Ok, there were moments when there were apparently more sharpness at 24-105. But that turned out to be little difference in the AF. After adjustment of focusing and re-focusing the recording levels were the same in both optics and thus the sharpness. Perhaps a touch more sharpness in the edge region at 24-105 (you will never see in prints on paper!). I can not say anything about the contrast. There was no appreciable advantage for the 24-105. Conclusion: If you really need the 4-panel including 24mm focal length and the significantly better processing (and rubber seal on the Bayonet) to estimate know, will find at 24-105.. Who the image quality is most important, for cutting back on processing quality and intensity in purchasing takes, gets the same picture results at half the price. Especially since I do not like handling when adjusting the 24-105. The rings for zoom and sharpness are compared to the 28-135 reversed. This means you have to turn on the camera body for zooming quite close the ring, which I find quite verkrampfend. My choice is always already fixed for 8 years and I almost fainted, but for this comparison is clear that there need not be L-lens, in this case, if you want to make the best pictures.
