My Video Review of the Canon 24-70 f/4 IS vs 24-70 f/2.8 vs 24-105 f/4 ISPart IPart IICURRENT CANON REBATES AND SAVINGS UPDATE -Since posting this information I have tested and reviewed the Sigma 24-105 f/4. Watch my review of the Sigma 24-105. It is significantly sharper than the Canon 24-105. Early Thoughts - the new 24-70 f/4 is VERY nice - sharp, the IS works very well and I would have taken it over the 24-70 f/2.8 on my vacation travels without a second thought - it is lighter, smaller and offers an excellent macro feature. My next question is would I prefer it at a wedding over the f/2.8?  A stop of light is hard to give up but if this lens had been available when I bought I think I would have picked it and been able to sleep a bit better at night saving a $1000 dollars.  Sharpness, color, contrast and chromatic aberration control all seem on par with the more expensive f/2.8 - so it really comes down to that stop of light.  Oh and the IS. I think the IS is excellent for general photography and of course travel, it is not as helpful on the wedding day dance floor.  And another OH - the Macro isn't going to be the Canon 100mm f/2.8, my go to standard for all Macro lenses but it certainly comes close, shockingly close for someone that just likes to dable in macro now and then. . .   I also thought I would see more bokeh difference shooting at f/4 vs f/2.8 and really see much less than I expected.  Checking the charts it makes sense - the differences in depth of field between the two at normal shooting differences is slight.All three lenses are excellent and they should be when we are talking about the cheapest(24-105 f/4 IS USM) being almost a grand.The Canon 24-70 f/2.8 Mark II is currently selling for $2200 (Buy from Amazon). I have shot several thousand wedding images with this lens over the last three months and it is a fantastic lens. Sharp wide open though I did have to slightly adjust focus.  Color rendition is gorgeous, contrast is top notch - it is really easy to run out of superlatives when describing this lens - Downside are price, no IS, it is a hefty piece of glass with a huge 82mm filter size and it is only so-so at close focusing.   I recently took it on  vacation and loved the images but felt I would have been happy with a smaller lens and or a lens with a bit more range.  Before I bought Canon's 24-70 I tried the Tamron 24-70 f/2.8 with VC (Buy from Amazon).  It required serious micro AF adjustments and I repeatedly got lens communication errors, something I have never seen with the Canon.  I know there are plenty of photographers happy with the Tamron lens and there are plenty of sharp copies out there.  For almost $1000 less you get f/2.8 and IS - you just are taking a bit more of a gamble, in my opinion. Some Tech Specs - 28.4 Ounces with 1 Super UD lens element and 2 UD lens elements and 9 bladed aperture.The new Canon 24-70 f/4 IS sells for about the same (Buy from Amazon)  It is a bit lighter, has a suprisingly great macro mode, very good Hyrbid IS and a nifty pinch cap(Bout Canon) this might seem silly but it makes removal of the lens cap MUCH easier when the lens hood is on and facing out.  You do lose one stop of light going from f/2.8 to f/4.   Filter size is a more wallet friendly 77mm.    Weighs 21 ounces - 2 aspheric and 2 UD elements and 9 bladed rounded aperture.The  24-105 f/4 IS(Buy from Amazon) has been around for sometime, it has been a while since I used it, last shot a wedding using it, great lens and an excellent value for an L lens, can be found for $860. filter size is also 77mm.  Weighs 23.6 ounces with 1 UD lens element and 8 bladed aperture.