I have been a satisfied user of 24-105 f4L for a few years. Unlike some others, I found it very sharp even at 24mm. I dropped it on a trip recently and though it still works the filter ring is dented and it is difficult to get filters on and off. So based on reviews I just replaced it with 24-70 f4L and just took the first couple test shots at home.
Barrel Distortion. One of the selling points of the new lens is that it has much less barrel distortion at 24mm. Since that is the focal length I use most on this lens, it made the switch worthwhile. My test shots of the two lenses on the same metal door (tripod, exact same framing) show this is true. Notice how the right side and top side of the door bow slightly on the 24-105 and are straighter on the 24-70. The new lens appears brighter at the same setting (f/8). The new lens seems to be just a hair wider, though the difference is minimal (look at the dark bricks in the upper left corner).
Macro Mode. The other selling point of the new lens (besides being a bit sharper overall) is the dedicated macro mode. I took a ruler and the end of the lens was six inches away from the figurine. If you do not want to carry a separate macro lens (as I do not), this feature can be a real asset. The downside is that you have to be very close to the subject and have very little play - much like using an extension tube. The advantage to carrying a separate macro lens is you have the full range of focus from close to infinity. I enlarged the macro shot to actual pixels and it was incredibly sharp (unbelievably so) on the head of the figurine. The problem when you are that close is the body is out of focus due to shallow depth of field, even at f/16.
Conclusion. If you shoot this standard zoom mostly at 24mm (as I do), and shoot a lot of architecture (as I do), then it may be worth switching to the 24-70 f/4 for the improved barrel distortion. If you use the full range and you have a 24-105 that still works well, then it is likely not worth switching. If I had not dropped my lens I would likely have not switched. I have made no mention of the obvious alternative, the 24-70 f/2_8 (either I or II). That is a whole other discussion and there is already a thread on that.
Barrel Distortion. One of the selling points of the new lens is that it has much less barrel distortion at 24mm. Since that is the focal length I use most on this lens, it made the switch worthwhile. My test shots of the two lenses on the same metal door (tripod, exact same framing) show this is true. Notice how the right side and top side of the door bow slightly on the 24-105 and are straighter on the 24-70. The new lens appears brighter at the same setting (f/8). The new lens seems to be just a hair wider, though the difference is minimal (look at the dark bricks in the upper left corner).
Macro Mode. The other selling point of the new lens (besides being a bit sharper overall) is the dedicated macro mode. I took a ruler and the end of the lens was six inches away from the figurine. If you do not want to carry a separate macro lens (as I do not), this feature can be a real asset. The downside is that you have to be very close to the subject and have very little play - much like using an extension tube. The advantage to carrying a separate macro lens is you have the full range of focus from close to infinity. I enlarged the macro shot to actual pixels and it was incredibly sharp (unbelievably so) on the head of the figurine. The problem when you are that close is the body is out of focus due to shallow depth of field, even at f/16.
Conclusion. If you shoot this standard zoom mostly at 24mm (as I do), and shoot a lot of architecture (as I do), then it may be worth switching to the 24-70 f/4 for the improved barrel distortion. If you use the full range and you have a 24-105 that still works well, then it is likely not worth switching. If I had not dropped my lens I would likely have not switched. I have made no mention of the obvious alternative, the 24-70 f/2_8 (either I or II). That is a whole other discussion and there is already a thread on that.
