Teleconverters RF vs EF

AwesomelyBad wrote:

I'd honestly expect some difference between the performance of the EF and RF extenders on the EF/RF versions of the 600mm, just due to the fact that they're intended for lenses designed for different flange distances. I wonder if the assumption for RF versions of the big white lenses was that the image as projected by the rear element is close enough to parallel to the sensor that the position of the teleconverter wouldn't make as much of a difference (particularly since the RF teleconverters seem to be optically better than the EF versions).

I doubt there are too many people with both the EF and RF versions of the 600mm sitting around that could do a proper controlled comparison on the same body though :-D.

The question isnt the optical difference between a EF and RF teleconverter.

The question is how does the added space (distance) on a RF lens between the rear element of the RF lens and the RF teleconverter affect image quality.  Comparing the distance between the EF 600 f4 iii rear element and the front element of a EF 1.4x iii teleconverter VS the distance between a RF 600 F4 rear element and the front element of a RF 1.4 teleconveter - the RF combo the distance is quite a bit more than the EF combo - the length of the RF to EF adapter to be exact.  Again, the RF 600 F4 and the RF 400 F2.8 lenses are identical lenses to the EF 600 F4 iii and the EF 400 F2.8 iii, except the RF versions have a RF to EF adapter welded onto them.  Canon even states this on their website under the product descriptions for the RF 600 and RF 400 lenses.

I dont think the statement of the RF teleconverters were designed for a different focal plane because put a RF teleconverter on the RF 100-500 and zoom the RF 100-500 all the back as you can (approximately 300mm) and the back element of the RF 100-500 is practically touching the front element of the RF 1.4x teleconerter.

Asking the question a different way, take any lens/teleconverter combo (staying with the same format of EF or RF), put an extension tube between the lens and the teleconverter, and how does that effect image quality?  That is in effect what Canon did with their RF 600 F4 and RF 400 F2.8 lens by incorporating the RF to EF adapter into the lens.

Shawn