2" longer seems like a fine compromise to add a built-in TC. I doubt Canon decides the design of telephoto lenses based on if it can fit overhead bins of aircrafts.. I hope the field use of the lens determines the design. Field use design must keep in mind the dust and time factor of adding a TC. It is what it is, but a built in TC would have worked better...According to Canon, for the 100-300/2.8 it was about both weight and size. Based on the patent, the 200-500/4 is the same length as the RF 600/4 (longer than the RF 800/5.6). Those lenses are already at the edge of fitting in an airline-regulation carryon. My 600/4 II is slightly shorter than the patent-based lens length of the 200-500, and here it is in a carryon:
View attachment 210590
A built-in TC would make the 200-500/4 something like 50mm / 2” longer, meaning it wouldn’t fit in a standard carryon. I suspect that factors into Canon’s decision.
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