Canon 24-105mm f/4 L IS vs. 24-70mm f/2.8 L lens

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.

I have no expertise on this question, but for me a significant factor in the choice but be what other lenses I had and the ranges they covered. I dislike carrying a lot of equipment about, unless I am going somewhere specifically to take photographs and so I try to acquire lenses that do not overlap too much. As I dislike having to lug about a flash, maximizing light input is also a factor.

I own the 24-70 and find it to be very good.;)
But on the other hand, the 24-105 is more flexible precisely because it goes from 24 to 105, which makes of it an all around lens.
However, the larger aperture is a must and always an advantage. Even without the IS.
Consider you are using a MKIII: the accuracy of focusing is better because the lens is a f/2.8.
My lenses are all f/2.8 and I do use the flash to fill the shadows and in other situations.
:)

Personally, I prefer the Canon 24-105mm F4 L IS USM to the Canon EF 24-70 F2.8L USM because the extra 70-105mm translates, in the real world, to twice the distance. In most cases, this makes the lens an excellent travel or on-the-street choice. If you're considering the EF 24-70, I strongly recommend that you test the lens to assure it isn't a lemon. Perhaps that is no longer an issue, but when I purchased my EF 24-70 a few years ago, these lenses had a quality-control issue, and unfortunately, my particular lens was not sharp, even after I sent it back to Canon for tweaking. Indeed, before and after Canon tried to fix it, I compared it to the much less expensive Tamron AF 28-75mm f/2.8 XR Di Autofocus Lens and found the latter to be sharper, at least in the center. My comparison tests and comments appear at http://lubowphotography.com/tamron-canon-test.htm. Since then, I've shelved my EF 24-70 and now park the EF 24-105 on my camera -- and when F2.8 is needed, I'll use the Tamron.

Both lenses are great, and i am happy with both.
I use 24-70 because it is my first L lens and i like 2.8 in many conditions.
I use 24-105 for more reach if walkaround sometimes, and IS can be handy as well, now i use my 24-105L outdoor more because my 24-70 has a filter damaged and stuck on it.

I purchased this lens used at a very good price from a pro photographer who was converting from that lens to the 24-105L. As soon as the new 24-105L lens came out many photographers were dumping their perfectly good 24-70L lenses on the used market and, for a short time, the prices of a used 24-70L dropped drastically on eBay because the influx of used 24-70L lenses outnumbered the bidders for that type of lens.

I like the 24-70L lens very much but, I have replaced it for my day-to-day walk-around and travel photography. Since I use 1.6x format equipment (30D and 40D) I have switched to the 17-55mm f/2.8 IS lens for those purposes.

However, I stll use the 24-70L, rather than the 17-55mm as a studio lens because:

1. The extra weight of the 24-70L is not a problem in the studio since I don't have the camera hanging around my neck all day.

2. I like the extra 15mm on the long end for head and shoulder portraits. Yes, I would like the 17-55mm lens to cover the 17-70mm range but, I would not give up f/2.8 for the extra 15mm.

3. The rather narrow 24mm end doesn't bother me in studio shooting since my studio is big enough to back up.

4. The lack of IS is a non-factor in studio work since I always use studio flash.

5. The closer focusing distance of the 24-70L (1:3.5 ratio) allows me to use this lens when I would have needed to switch to a macro if using the 17-55mm.

I would prefer this lens over the 24-105mm for studio work because I can control depth of field more closely with the f/2.8 than I could with the f/4 aperture.

All of the above is true but, if I had owned the 17-55mm before the 24-70L, instead of the other-way-around, I seriously doubt if I would have purchased the 24-70L.