Yeah, I think it was designed without a front filter or built-in teleconverter in mind from the start.The other big whites (500 mm f4, 400 mm f2.8, 600 mm f4, 800 f5.6) are all larger in diameter and 112 mm is the largest commercially available threaded filter available (based on my searches at B&H). Basically, the 300 mm f2.8 would be the only big white compatible with a threaded filter. It is interesting that Canon made this decision because to my knowledge the RF 100-300 mm f2.8 is the first 300 mm f2.8 lens to ever use a threaded front filter.
Nikon made the same decisions with their 120-300 f/2.8.
Nikon could quite easily use the same optics and make a Z-mount version with plenty of room for both a teleconverter and drop-in filters.
Upvote
0