That's not what I'm talking about at all - What I mean is simply a single unit as if you combined the RF adapter and converter together but having the switch move the optical elements just like it does on the 200-400. Having the extra 1.4 at the flick of a switch is much nicer then putting off and on extenders especially in crappy conditions.
But a switch to place optical elements in the path of the lens' optical formula from the side is fundamentally different from a switch that would lengthen or shorten the lens barrel by 24mm.
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