Greetings, With the addition of a FD to EF adapter + a canon R adapter, you might get the lens on the front of an R series camera, but there will be zero communication. So everything would be manual. The R10 is an extremely capable entry level MILC camera, you would be doing yourself no justice trying to use 50 yr old lenses with it. Compatible with most telephoto and zoom lenses within Canon's flagship professional L-series, the Canon Extender EF 2x III is a great kit addition. Outstanding image quality at double the distance This extender's smart design ensures no loss of lens performance or image quality whilst doubling your focal length. TS-E 17mm and Extender EF 1.4x not working on EOS R in EF & RF Lenses 12-19-2023; Lens Extender compatibility with EOS 5D Mark IV and EF 70-200 f/2.8L IS II USM lens in EOS DSLR & Mirrorless Cameras 12-19-2023; Extender EF 1.4x III compatible with EF mount? in Camera Accessories 12-18-2023; EOS Rebel T6 Extender and Lens Recommendations in EF This Smugmug gallery has 5 shots I took of the moon last May using an EF 800 f5.6 bare, with a 1.4x, a couple with a 2X, and the last with a Celestron CPC 1100 (equivalent to a 2800mm f10 lens) using a 1DX III. The lens data for each image is available in the information button, the telescope shows Anyone got the R6 + EF 70-200/4 IS II + EF 2x III? Since this combination is also absent from the 20fps compatibility list I wonder if that is really true. Even the old version of this lens without IS supports both 1.4x III and 2x III with 20fps. 600/800MM lenses vs RF 2x Extender for Kenya Safari in EF & RF Lenses 12-06-2023; Extender EF 1.4x compatibility with Mount Adapter EF-EOS R in Camera Accessories 12-05-2023; EOS Rebel T3 RF lens compatibility in EF & RF Lenses 12-04-2023; R7 auto-iso on viewfinder display with flash in EOS DSLR & Mirrorless Cameras 12-03-2023 1. 2X III works really well and maintain a reasonable sharpness only on Superteles, 100-400 II and on on 70-200 II and unfortunately not included the 100-400 I. It's a waste of money. kingfishers are one of the skittish creatures, it posts a challenge even with 600mm + 2x. If you use a 2x with 400, you may find the distance not usable as you Again, IMHO. BTW, Sigma makes a 1.4x converter, the Sigma TC-1401 1.4x Teleconverter for Canon EF. It would be a better choice than the Canon which is designed bascially for Canon lenses and not Sigma's. EB. EOS 1DX and 1D Mk IV and several lenses! I was using them with the 70-200 f/2.8 IS USM MkII and the 100-400 IS USM MkII zooms and found that the 2.0 extender degraded the results unacceptably - I was using them with Cano 5D IV, DsR, 7DII and 90D bodies. While I have had no issues using the same lenses on the R5 and R6 bodies I have, I have not considered using them with extenders. A user with something like a EF 70-200mm f/4L IS USM can add a 2x III TC and get a 140-400mm f/8 lens that will have most or all of the AF points available on their camera (depending on model). Caveats (Supported Lenses and Stacking) Canon’s extenders, both the 1.4x III and the 2x III, have front elements that project into the rear of the g81RMk.