It will depend upon the lens (only compatible with certain fixed focal length lenses). See the specifications HERE. And also do look here: EOS 90D Supplimental Information (search that PDF for 2x). It will show all the compatible lenses along with what group the camera will clasify things (A, B, The 2x extender lost 6 f-stops with this configuration, the camera wouldn't go wider than f11 vs. f5.6 normally. Check other reviews and tech specs - I thought it wouldn't be as many f-stops so maybe this was something to do with the body I was using. Extender EF 1.4x III – 72 x 27.2 225 Extender Cap E II – LP811 – – – – – – Extender EF –2x III 72 x 52.7 325 Extender Cap E II – LP811 – – – – – – EF ZOOM LENSES EF 8–15mm f/4L Fisheye USM Filter Holder 78.5 x 83 540 Lens Cap 8‐15 EW‐77 (15mm only LP1219 – – – ‐ – wrote: The Canon EF 70-300mm DO USM manual says it will not work with the EF 2X II extender. Will it work (particularly the IS) with the newer EF 2X III extender? thanks Jerry No, it will most likely not be fully compatible with that lens. Check the compatibility chart. PB0wo5.