Nikon 800 E FL had that "matched" 1.25x external TC that came with the lens.
Not sure how "matched" each of those were.
There was nothing to compare with as you couldn't buy a generic 1.25x and see how it compared to the "matched" one.
EB-1 wrote:
The 1.4x III was a little better than the internal TC of the 200-400/4. I no longer have access to optical engineers to explain if it is a true limitation or depends on the particular combination. Maybe a lens designer here can chime in.
EBH
I'm not a lens designer and I can't quantify how much difference it makes, but a principal difference between external and internal TCs is that external TCs extend the total length of the optical path whereas the internal ones do not. So you clearly can't use the same design. This might be an advantage for the external one, as shallower angles are easier to compensate. A probably bigger advantage for internal TCs is that they are (usually) not the last glass in the optical path, which opens design flexibility that does not exist for external TCs.
As long as the image quality is close, the internal TC is obviously far more useful for action photography.
A flip of your finger to engage and disengage the internal TC beats the speed of external TC swapping by a country mile.
