This website has received quite a few questions about whether the Canon 24-105 mm f/4L IS lens is a better option than the 24-70 mm f/2.8 non-IS lens. This is quite an important question because for many photographers, either lens is their most-used / "workhorse" lens. In a nutshell, here's quick list of the pros/cons of each lens:
Advantages of Canon's 24-105 mm f/4 L IS Lens- Image stabilization (3 f-stop version)
- 30% lighter and slightly narrower and shorter
- Extra focal length reach from 70-105 mm (although this is slightly softer)
Exact Specifications
Weight: 1.5 lbs (670 g)
Length: 4.2 inches (107 mm)
Minimum Focus Distance: 1.48 feet (0.45 m)
Maximum Magnification: 0.23X
Advantages of Canon's 24-70 mm f/2.8 L Lens- Faster maximum aperture of f/2.8 (with brighter viewfinder image, improved autofocus accuracy)
- Substantially less vignetting at the wide end
- Slightly more efficient lens hood design (particularly at the long end)
- A little less barrel/pincushion distortion
Exact Specifications
Weight: 2.1 lbs (950 g)
Length: 4.9 inches (123.5 mm)
Minimum Focus Distance: 1.25 feet (0.38 m)
Maximum Magnification: 0.29X
Other Notes
The lenses are very, very similar in terms of sharpness/contrast. For all reasonable purposes they are tied in this respect. Both take 77 mm filters, both are ~83mm at their widest point, and both are similarly priced. On the other hand, a notable difference that is less often mentioned is that the 24-105 mm lens has even less light-gathering than most f/4 lenses. In other words, you still get the same depth of field as you would otherwise get with f/4, but you may need a slightly longer exposure time at the same ISO setting.
Overall
First and foremost, it really depends on your intended use and how much weight you allocate to each lens's traits. If you're doing photojournalism-style people shots or weddings you'll probably prefer the 24-70 mm lens. Otherwise the 24-105 lens is superb for hand-held landscapes and other travel photography.