Canon EF Extenders (Mark II vs Mark III)

I've tried to do some research on this before posting, and the consensus of what I can see online is that:
- For 1.4x the difference in IQ between the II and III is minimal
- For the 2x the difference in IQ between the II and III is enough that it's worth getting the III over the II.

Can anyone with experience with these extenders weigh in? This is something I'm considering to pair with a future R5 or R6 and my current Canon 100-400mm II, if that makes a difference. Not my current 7D unless I feel like manual focusing.

Thanks!

I can answer but partly.

i haven’t used Extender II but use Extender III , both 1.4x III and 2x III , with EF 300 mm F/2.8 L II lens on 5D Mark IV body.

IQ with Extender 1.4x III is hardly affected. Excellent sharpness and details at F/5.6 . Even at F/4 IQ is very good.

IQ with Extender 2xIII is affected. At the start F/5.6 picture quality is poor. Starts improving from F/6.3 onwards till F/8.

This leads to high ISO but used with R5 or R6 this will not lead to noise issues as these two mirrorless bodies handle high ISO very well as being reported.

I also haven't used Extender II but use Extender III , both 1.4x III and 2x III

On my 5D Mark IV I was always disappointed by the results of the 1.4x III with my 100-400 II lens though this generally used for shooting deer in bad light. It was however great for shooting the moon.

I recently purchased the Canon R6 and have used both the 1.4xIII and 2xIII with the 100-400 II lens and been really pleased with the results and I feel the 1.4x III produces much better results on the R6.

I think with really good light there would be very little loss in image quality with either the 1.4 or 2.

I traded in the 1.4 EX Mark II towards the purchase of the Mark III.
Well worth the upgrade.
With an R5 in my future as well, why waste money on older design Mark II.
I have no experience with either 2.0 Extender. If I bought one today, the Mark III.

I've shot extensively with the Canon extenders version 1, 2 and 3 (less with 3, since I shot with the version 2 for over a decade)

My point of view differs from many. Going all the way back to the version 1 T-Cons, the 1.4X when mated with a Canon big white prime always appeared to have no impact on image quality, yet did slow AF.

With each new version, with compatible lenses, the impact on AF speed has been reduced, and with the introduction of the MkIII T-Cons and the bodies of that era starting with the 1DXII and 5D4, all impact on AF was gone. they auto-focused just like with a bare lens.

I can not see a difference in IQ. In fact when the 1.4x II was released, it was said that weather sealing was added, superior optical coatings, but the lens assembly was unchanged. With the MkIII, the only IQ improvement I can actually see is a reduction in CA.

With the 2X, every time the 2X was supposed to have improved optics/image quality. Again, to my eyes, improvement has been minimal. Unlike the 1.4x, the 2X has always had a noticeable detrimental effect on image quality. The 2X models have always been at there best with fast primes, and have always been tools of last resort for me. That said, the MkIII also has significant improvements over the MkII where AF is concerned.

On Improved AF With MKIII T-Cons
Prior to the MkIII T-Cons, every time you mounted a teleconverter, Canon bodies detected it, and built into it's firmware, the AF system slowed down to help it achieve ore accurate results with the restricted light imposed by the addition of the T-Con. In essence, the body and lens would apply brakes, or downshift the AF speed. The 2X imparted a much bigger hit on AF speed than the 1.4x. With the MKIII T-Cons and the most modern DSLR AF Systems these "brakes" were finally removed. BUT, ONLY If you had all three of the correct ingredients to make this work;

- You had to have the most modern af system in the most up to date bodies. This included 1DXII, 5D4, and 1DXIII. (and maybe 90D, don't have first hand knowledge there)

- You also needed a compatible lens: Version 2 IS telephotos, and version 2 IS zooms

- Of course, you needed to use the MkIII T-Cons.

Substitute any part of the chain, and AF brakes would be applied.

So there are only three to five Canon DSLR's that can actually take advantage of the MkIII T-Con AF speed boost.

As for EOS R mirror-less? To the best of my knowledge the contrast AF in the R Series does not have this AF system downshift at all. More testing will confirm, but I've been testing with a pair of 2X converters stacked, and AF seems fast and accurate. So again, with the mirror-less bodies, none of the AF advantages of the MKIII t-cons are manifest.

Thanks for everyone weighing in! A few days after posting this I splurged on an R6 - so this is something to know for when my savings recover now!

The information here been invaluable though. I think I am definitely more confident that the extenders will work well with my 100-400 II and R6 combo, and make me lean more towards the 1.4x as the priority.

So after reading your post, I am confused as I am a beginner and do not yet understand some of the jargon. I have a 1dxii and a 400mm 5.6L.
I need more reach. What can I purchase that will not affect sharpness or auto focus speed?
Thanks

whyfret1 wrote in post #19181840
I need more reach. What can I purchase that will not affect sharpness or auto focus speed?
Thanks

Your best option is to sell the 400/5.6 and pick up a 5/600/F4 and 1.4x III. Next best option is to keep the 400/5.6 and use it with the 1.4x III.

I own the 1.4x II and III, AF improvement alone makes the 1.4x III worth the cost.

(I owned the 400 and sold it quickly when I purchased the 500.)