TC Test: Canon 2x vs Kenko 2x vs Kenko 1.4x (stacked)

So, I decided to run a little test tonight. I wanted to see how all my current TCs performed against one another. As the title says, Canon 2x vs Kenko 2x vs (stacked) Kenko 1.4x

Here's what I used:
1). Canon 2x TC (mark1)
2). Kenko 2x Pro 300 DGX
3). (2x) Kenko 1.4x Pro 300 DG
4). Canon 1d mk2 body
5). Canon 70-200mm IS 2.8 mk1
6). Benro TravelAngel C-068m8 CF tripod + B-0 ballhead

AV mode, IS off, I used a 10-second delay on shots to mitigate shake (misplaced my remote), set to 640 ISO, using apertures f/5.6 and f/8. Focal lengths set at 400mm (Canon 2x), 400mm (Kenko 2x), and 392mm (2* Kenko 1.4x) with additional 1.3 magnification due to APS-H.

After going over all the images at 100% and comparing the exif data, I've come to the following conclusions:
---sharpness at matching apertures was similar for all 3 TC combinations
---stacking TCs leads to incorrect reporting. I had to adjust test apertures to f/4 and f/5.6 to get proper results with the stacked 1.4x TCs (otherwise too sharp at f/5.6 and f/8)
---darker overall exposures with the Canon 2x TC, followed by Kenko 2x, and finally the stacked 1.4s
---fastest shutter speeds for the Canon 2x, followed by the stacked Kenko 1.4s, with the Kenko 2x being the slowest

Shutter Speed Results:
Canon 2x: 1/20@f/5.6, 1/8@f/8
Kenko 2x: 1/10@f/5.6, 1/5@f/8
Kenko 1.4x: 1/15@f/4, 1/6@f/5.6

I don't have a Canon 1.4x TC to compare against at the moment, but you can probably assume that in a direct comparison with a Kenko Pro 300 1.4x TC, the Canon would provide faster shutter speeds AND a slightly darker image, with similar image quality. Using stacked 1.4x TCs might be an interesting compromise over 2x TCs, but you'll end up with inaccurate EXIF data, which isn't worth it in my book.

I may upload some of the test shots, upon request. I won't bother if no one else cares.

I care !

MOkoFOko wrote in post #11715804
[B]---stacking TCs leads to incorrect reporting. I had to adjust test apertures to f/4 and f/5.6 to get proper results with the stacked 1.4x TCs (otherwise too sharp at f/5.6 and f/8)

stacking two of the same yes, but stacking a 1.4x and a 2x reports correctly. Thats because one pin is for 1.4x and one is for 2x

I care too....I'm pondering either another 1.4 or going with 2!

I used to own 7 different TCs. I am down to 4 now. Have done extensive testing. Results will depend on what lens you are using. Different TCs and combinations of TCs work differently on different lenses. There is no one answer. Generally though I can say that if you are stopping down a lot, 2 1.4x TCs will look about the same as a 2x TC with the advantage of the camera only can see one TC at most = AF sometimes with the 2 1.4x combo. But, wide open (or one stop down) there is a differnece between 2 1.4x and a 2x - the 2x wins.

gasrocks wrote in post #11717069
I used to own 7 different TCs. I am down to 4 now. Have done extensive testing. Results will depend on what lens you are using. Different TCs and combinations of TCs work differently on different lenses. There is no one answer. Generally though I can say that if you are stopping down a lot, 2 1.4x TCs will look about the same as a 2x TC with the advantage of the camera only can see one TC at most = AF sometimes with the 2 1.4x combo. But, wide open (or one stop down) there is a differnece between 2 1.4x and a 2x - the 2x wins.

At one point or another, I had my hands on every canon mark1&2, every Kenko pro300 DG and DGX model, and the 1.4 sigma and tamron. This is the first time I've decided to compare multiple copies though. It mostly goes without saying that there will be slight variations between models, but for the most part, the results should be about the same. As for lenses, I would assume that wouldn't be a factor, since that would be the one single constant in every test?

It would make sense that two stacked 1.4x TCs would underperform against a similar 2x TC--more glass and more space introduces the possibility of further image degradation. From my tests though, it really does seem like the stacked 1.4s hold their own. Performance at 100% crop was practically the same across the board. I'd probably go with stacked 1.4s instead of a single 2x--but the incorrect EXIF data annoys me too much.

Upload plz