So while the new 200-400 is just a touch outside of my budget right now, I'm left wondering if they can take the technology involved in the 1.4x TC in that lens and put it into a new "external" version that could be switched on/off. I dream about leaving my TC on the camera/lens and only turning it on when I need it.
Forgive me for being completely ignorant about lens construction. I'm sure somebody is about to point that out.....but why can't it be done? Even if the teleconverter is twice the size of the current models, I would consider that a worthy trade-off to not struggle with a lens change every time I want to use my teleconverter.
I apologize if this has already been brought up and I missed it.
It would need some in place optical elements just to deal with the extra extension. They can do it in the 200-400 because its taking up pretty much unused space as it is.
The 200-400 TC can be simply removed out of the optical path. That means that without it in place, the lens still focuses light on the film plane. If you were to design such a TC for "normal" lenses, it would be akin putting an extension tube between the body and lens, thus not focusing the light on the film plane at infinity anymore.
So in other words the lens has to be specifically crafted to support this. Normal lenses won't work.
