The first lens to feature this technology was the EF 300mm f/2.8L USM, introduced in 1987. Since then, Canon has produced a range of lenses featuring USM technology, including both their premium ā€˜Lā€™ series lenses and more affordable options. Focal Length and Maximum Aperture: 24-70mm, 1:2.8. Lens Construction: 18 elements in 13 groups. Diagonal Angle of View: 84Ā° - 34Ā°. Focus Adjustment: Inner- focusing with USM. Closest Focusing Distance: 0.38m/1.25 ft. Zoom System: Rotating Type. Merchandise type.
None of Canon's Teleconverters are compatible with the EF 24-70mm F/2.8L USM series lenses. I would look into a longer lens instead of using a teleconverter. With the 1.4x teleconverter you loose 1 stop of light.
The EF 24-70mm f/2.8L II USM is a near-flawless lens with optics that come very close to matching a set of top-quality primes. With fast, accurate autofocus and weathersealed construction, it's difficult to find any really serious faults at all.
These Canon lens filter charts show the filter sizes Canon lenses, including zoom and prime lenses with EF, EF-S, EF-M, and RF mounts. EF 24-70mm f/4L IS USM

For you, I'd suggest the RF 24-105L f/4 IS, and if funds allow it in the future then supplementing it with the RF 70-200 f/2.8L IS or get a used EF 70-200 for a lot less. I would also look for a third party EF f/1.4 or f/1.8 fast prime to serve as a portrait lens and adapt it onto the R.

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canon ef 24 70mm f 2.8 l is usm lens