This is probably one of the most commonly asked questions since the launch of the new Canon EF 24-105mm f/4 IS lens. There’re always pros and cons. The EF 24-105mm f/4 lens has the 3rd generation IS from Canon that gives you 3-stop Image Stabilizer for outstanding camera shake reduction. It has longer reach in the focal lengh (extra 35mm) and it is .7″ shorter, .2mm narrower and .6 lbs. lighter than the EF 24-70mm f/2.8 L.

However, there’s a flare issue at the launch that prompt the recall of all new Ef 24-105mm lens. It’s slower than the 24-70mm lens, which gives you a constant f/2.8 aperture for shooting indoors and produces a very nice bokeh (background blur) when shooting portraits. Another advantage of the 24-70L lens is the extra AF accuracy when using the center AF point under low-light situations. Here’s the summary of the comparison from The Digital Picture:

“Price, build quality, image quality … differences will likely not affect the purchase decision of many. I found the Canon EF 24-105mm f/4 L IS USM Lens to be at least as sharp as or slightly sharper than the 24-70 L at similar apertures (including f/4). At 70mm, the 24-70 L is slightly sharper than the 24-105 L until stopped down slightly. The 24-105 L has less light fall-off wide open than does the 24-70 L wide open, but the 24-70 has a slight advantage at comparable apertures. Color and contrast of the 24-105 L are at least as good as the 24-70 L. The 24-105 L has slightly less CA than the 24-70 L. Both are very good in this regard only showing CA in harsh situations at their widest focal lengths.

I am sure that many Canon EF 24-70mm f/2.8 L Lens owners will be adding the 24-105mm L to their kit. Indoor event photographers will *probably* select the 24-70 L and landscape/outdoor and portrait photographers might prefer the Canon EF 24-105mm f/4 L IS USM Lens.”

Website : EF 24-105mm lens Review from The Digital Picture

Bill Caulfeild-Browne from Luminous Landscape compare the two lenses from another viewpoint and the conclusion is :

“At 24 mm the 70-105 mm lens is definitely better at the edges at f4 and f5.6. This finding is slightly surprising to me as f4 is the maximum aperture for the 24-105 mm lens, whereas the 24-70 mm is stopped down by one stop. By f8 the lenses are hard to tell apart. They are equally good at the centre.

At 35 mm the lenses are practically identical and I’d only give a very slight edge to the new lens, and only at f4. The difference is more one of contrast than resolution, to my eyes. The 24 -70 mm seems to have just a teeny bit of flare around small details.

At 50 mm the same applies; a tad better contrast from the new lens but otherwise it’s hard to discern any difference.

At 70 mm I can’t tell any difference between the two lenses.

I’m a nature and wildlife photographer. Linear distortion is not a big deal most of the time, and vignetting is easily compensated for in Camera Raw. On the other hand, weight and size are issues that interest me, my neck and my back! And as I age, I find IS increasingly valuable even at modest focal lengths. So for me, the new lens is a no-brainer, especially when I don’t have to accept any less resolution, – and I get an extra 35 mm of reach!”

Website : Lens comparisons at Luminous Landscape

Website : Samples images for comparison from Bob Clark