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Archive 2016 · Order of stacked teleconverters

  
 
alundeb
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p.1 #1 · p.1 #1 · Order of stacked teleconverters


Not that anyone cares, but I just had to check if the order of stacked teleconverters affects image quality. It appears it does. The best teleconverter or that one designed optimally for the lens should be closest to the lens.

My most TC friendly lens at the moment is the Canon 70-200 2.8 L IS II. The teleconverters used in this test are the Canon 2x III and the Sigma APO 2x EX DG. To be able to stack them in both orders (The Sigma can be stacked directly on the back of the Canon), I used a 12mm extension tube between the teleconverters. It was used in both setups.

Test wide open at 200mm x2 x2 = 800 mm f/11. Camera was Canon 5DS R. Images shown are unscaled pixel crops with zero sharpening.

In order to rule out focus errors, I used the EOS utility on my laptop and shot tethered in LiveView. Manual electronic focus by stepping through optimal focus one step at a time. This step can be done with a button. I stepped through many images, found the best focus, and then used a sequence of 5 images around.

The results are consistent, and the order of stacking is more important that small focus errors or small camera vibration.

Canon first then Sigma to the left, and Sigma first then Canon to the right. Focus -2 top and Focus +2 bottom.

http://i306.photobucket.com/albums/nn242/Overflate/TC_CS_SC_zpsmjakjfcp.png



Apr 06, 2016 at 02:07 PM
RustyBug
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p.1 #2 · p.1 #2 · Order of stacked teleconverters




Good to know.
Curious now about a Canon TC + extension tube vs. extension tube + Canon TC vs. Sigma TC + Ext tube vs. Ext. tube + Sigma TC.


I realize that the tube was needed to allow for the mating of the TC's, but I can't help wonder how much influence that had in the outcome (although it would seem as a constant).

I know I had done some testing some time back with stacking TC's and I didn't get nearly that distinctive of a difference. Maybe my TC's were just closer together in IQ that it didn't matter that much @ 1.4X & 2.0X (both Sigma DG's) regarding the order.



Apr 06, 2016 at 03:32 PM
Zenon Char
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p.1 #3 · p.1 #3 · Order of stacked teleconverters


That is interesting and good to know. I stacked a Canon 2X and Sigma 2X on my 300 for my moon shot bit did I ever have to work the sharpening in PP.


Apr 06, 2016 at 03:48 PM
jcolwell
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p.1 #4 · p.1 #4 · Order of stacked teleconverters


Very interesting test, Anders. Thanks for posting.

When you say "Canon first then Sigma", does that mean the Canon is closest to the lens? I figure it probably does, but I just want to be sure.



Apr 06, 2016 at 03:50 PM
jcolwell
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p.1 #5 · p.1 #5 · Order of stacked teleconverters


RustyBug wrote:
I realize that the tube was needed to allow for the mating of the TC's, but I can't help wonder how much influence that had in the outcome (although it would seem as a constant).


I can think of two effects of including the tube, one of which would affect IQ:

(i) MFD and "infinity focus" distances are reduced, and

(ii) imperfections of the TC "in front of" the tube will be magnified in comparison with the TC "behind" the tube.

Assuming that "Canon first" means the Canon is between the lens and the tube, then this result demonstrates that the Canon 2x III has higher IQ than the Sigma APO 2x EX DG.



Apr 06, 2016 at 04:05 PM
Liquidstone
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p.1 #6 · p.1 #6 · Order of stacked teleconverters


Excellent test that proves you're correct in your hypothesis in the other thread, Anders!

The IQ difference between the two setups (which should be proportional to the difference in optical performance of the two TCs) is very apparent, even to my unglassed eyes.



Apr 06, 2016 at 05:10 PM
alundeb
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p.1 #7 · p.1 #7 · Order of stacked teleconverters


jcolwell wrote:
Very interesting test, Anders. Thanks for posting.

When you say "Canon first then Sigma", does that mean the Canon is closest to the lens? I figure it probably does, but I just want to be sure.


Yes, that is what I meant.



Apr 07, 2016 at 12:29 AM





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