I use this with my 24-70/2.8L IS EF II USM and 70-200 2.8/L IS EF II USM lenses, and it gives me all the range I could want (well, I could always use the 500 or 600 mm heh heh ) . The quality is flawless. Worth every penny.

I have used the extender 2X III with canon EF 70-200mm f/2.8L IS II USM Telephoto Zoom Lens obtaining 140mm-400mm, which is sharper than canon EF 100-400mm f/4.5-5.6L IS USM.

I use this with my 70-200mm 2.8L IS II mostly for sports. Really sharp out to 400mm if you're stopped down to at least f/8. Focusing is less accurate than without an extender, but it'll still beat out non USM lenses.

I was really loving my Eos 70-200 2.8L IS USMII lens except that at certain times I was wishing that I had a bit more focal length for some far away shots. I was a little concerned over reviews of the 2X EF Extender that complained of slow focus when the extender was attached to the same lens. Yes it is a bit slower indoors and sometimes hunts for focus on subjects close in...but all things considered, it is a relatively quick and inexpensive fix for a 400 lens without investing $1600 or more in Canon's 100-400IS. As others have noted it has an F5.6 max aperture when attached to the 70-200 but I shot all day at 5.6 in San Francisco during the Pride Parade and loved the soft bokeh that it produced at this aperture. Also a lot lighter and less bulky that carrying two large telephotos around all day. I saw no other changes or adverse results with my lens while using this extender.

I use this with my 70-200 2.8L II, It maintains the image quality exceptionally well. The auto focus is nowhere near as fast with this lens, however this is rarely an issue for me. A great little workhorse overall.

I'm just an amateur photographer, but wanted this for my 70-200 2.8 ISII Gives extra range decent quality and decent pricing. Very happy with it this far

Use this product to double my 100-400mm zoom lens. What a difference it makes. I got beautiful shots of local wildlife at 400mm but with the extender added, it becomes 800mm and I can see their big brown eyes.

When combined with the Canon 70-200 f/2.8 USM IS II, this is one sharp add-on. In good light, it slows down the auto focus some. In poor light, it starts hunting. AF is very PRECISE with the Canon 70-200. Images are sharp and crisp. I don't have another suitable lens for this TC. I am not sure if it is a 100% replacement for a larger, more expensive lens or not, but as a simple way to double the reach without impacting IQ too much- it fits the bill and fits easily in the bag. I have been pleasantly surprised by the clarity of every shot I've taken with it so far. It is expensive for being just a TC. If you can only get the 1.4x III or the 2.0x III- get the 2.0x III- provided you can still autofocus.

The new 2x extender works pretty well. Better sharpness than the older model. Autofocus wasn't as fast or as accurate compared to just a straight telephoto lens while shooting with the 1D mark IV. I'm interested to see how it works with the new super telephotos when they start to become available next month. I favored shooting at F/8 because wide open at F/5.6 there was distortion beyond the point of focus.

I've used this extender only a few times and the images are sharp and clear. For the price and flexibility, I'm not disappointed with this item. The focusing is a little slow, as already noted in the product description. But since I do not take sports shots often, this is not a problem for me.