Canon calls this the RF135mm f/1.8 L IS USM: RF: Works only on Canon's EOS-R Mirrorless cameras. L: Expensive as L. IS: Image Stabilization. USM: UltraSonic (autofocus) Motor. Optics specifications top. Canon RF 135mm f/1.8 L IS USM Internal Optical Construction. UD elements. IS section. 17 elements in 12 groups.