So I bought one of these in the far past, and ragged it on an Amazon review, because of all the issues with this teleconverter. However I have been waiting a long time to get a Canon 2x III for a better price than $325, and haven't been able to snag one. So I decided to buy another, this time from Adorama, to see if perhaps the first one was flawed. Here is the mini-review, I hope you find it interesting.
I wanted 3 things.
1) I want to make my 70-200 f2.8 II a 140-400mm f5.6 lens for times I don't want to lug the Sigma 150-600 around for marching band, there is a difference over the course of a few hours.
2) I have a 1.4 and 2x Kenko set, and the Kenkos work on every lens (non EFS) I have tried them on, with no issues with exposure. However the 2x does ghost a bit, and I have to work a bit harder on those images to bring them back from the brink. I want something better.
3) I want to stack my TCs together for moon and other long distance shooting with 5.6x on the Sigma, or even to use just the YN 2x with Kenko 1.4x on my Sigma 150-600.
Let's get some of the superficial items out of the way. The color is a close match to the white L. The construction seems to match the Canon 2x. There is a weather seal ring on both sides of the TC.
How about the IQ? I don't know because I don't have one to compare, the TC delivers on IQ. It is much better than the Kenko which was one of my goals. I will post sample pictures below of what the 140-500 f5.6 results are from my 70-200. So Goal 1 was partially met (see following notes).
Now for the issues. The first thing you will notice is how the TC seems to report to the camera, because the aperture goes to 5.6 right out of the gate. However, AFMA (micro adjustment) doesn't see the TC+lens as a separate entity, like the Kenko does. This means that the TC is partially reporting. That leads to the next set of problems.
On any of the newer models, like the 5D4 and 7D2 and others (per reviews I have researched over the time of the first purchase and this one), this TC's partial reporting causes overexposure from 2 to 3 stops. You have to dial in EC in the Tv/Av/M w/auto ISO modes, or go to pure manual, or go to Live View. Older bodies don't seem to suffer from this, so if you have an older body, you might be okay. With a newer body, you have to go into this knowing you will over-expose 2-3 stops (variable depending on body).
Okay, so that issue isn't insurmountable. I can adjust EC, I don't like the case that I have to mess with the AFMA values affecting just the plain 70-200 lens when I am not using the TC. That is annoying too, but again, I can live with that.
So now I move onto the desire to use this TC on other lenses. Two issues arise out of this. First is that since the front element sticks out on the TC, any lens you have where the rear element moves in and out to being almost flush with the electronic contacts, you cannot use this TC. This could be much like the Canon as well, but I don't know. This means that I cannot use this on my 24-70 or 100 macro, not that I would really want to anyways.
I also cannot mix this TC into the other 2 Kenkos, they hit. The YN 2x has to be the last TC in the array before mounting the lens.
Finally I tried this on my Sigma 150-600, by itself, or as a mix in with Kenko, with taped contacts, etc, but the Sigma throws an error on the 5D4 right up front, and with the 7D2 when you hit the shutter. I get a lens error and the camera quits until I reset it. I then updated my Sigma dock and the 150-600 firmware, and still this issue persists.
So where does this leave me?
1) The TC works great on the 70-200 making it a 140-400, which is very handy in many situations, but creating an overexposure issue and AFMA nuisance. I can live with these.
2) I cannot replace my Kenko 2x because this new TC has issues with mounting to various lenses, so that doesn't work for me.
3) I cannot use it on my Sigma, so another goal not realized.
I think for $170, creating a lens that produces results that sit right between the 100-400 MKI and the new 100-400 MKII, this might stay in the bag. I don't know yet. It might go back. However, for those that only want to add some length to their 70-200 2.8 II, this might be a great option over the Canon at half the price.
Here are some pics of the TC and then some samples from the 5D4 and 7D2 at 400mm