I did a quick comparison between the two Canon extenders. I had given up the first one for stacking due to the barrel distortion and now I wanted to know whether there was noticeable difference between the two ... and there certainly was.
The absurd barrel distortion dropped to about a quarter of the previous value. It wasn't totally gone, though. The correction parameter "a" for ImageMagic was -0.00426 for the EF II and -0.00104 for RF. The correction without the extenders was -0.00013, so that had minimal effect even though I haven't yet figured how the magnification affects that number. Anyone happen to have the formula at hand?
There was also considerable loss of sharpness at the full frame extreme corners with the EF II and that seemed to be gone as well with RF. I say "seemed" as the base combinations were not exactly razor sharp there either. In any case the new one was clearly better.
About CA I'm not entirely sure. With S-K M-C 28 and DCR-150, I didn't see any CA, but the image was not that sharp. With Mitutoyo 10x and DCR-150 there was CA, and the older seemed to have somewhat more than the new one. There was CA without the extenders as well, so I suspect I just saw that magnified. The odd thing is there should not have been a difference if the other base lens didn't show anything with either one.
There was also a minor difference in magnification. The old one had 1.37 and the new one 1.41.
Last but least: The old one required taping of the pins, but the new one did not ... at least not on EOS RP.
Too bad I don't have EF 1.4x III to compare as well. It would be interesting to see when the improvements took place.
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