Canon 400mm 2.8L II w/ 2x III extender on 1DX. Aug 19, 2014. Just some samples in case someone else is looking for them (as I was before I made the purchase) since I realize the price point makes this an understandably rarer lens combination to find images of. I just got the 2x extender yesterday and took some pictures around the yard. There are few lenses that work as well with extenders as the Canon EF 300mm f/2.8 L IS II USM Lens. This shot was taken with a Canon EF Extender 2x III mounted for a 600mm focal length. The results are remarkable. 600mm f/5.6 1/2000s ISO 320 Horse Jumping. For some, this is the ultimate thrill. MSRP Price: $429. Made in: Japan. Production Status: In Production. Lens Description: Designed to extend a lenses focal length by a factor of 2x, the redesigned Canon Extender EF 2X III delivers optical performance on par with the finest Canon super telephoto lenses. It features a built-in microcomputer for seamless communication among camera Canon EOS 7D Mark II Canon EOS 5D Mark IV Canon EF 50mm f/1.4 USM Canon EF 100mm F2.8L Macro IS USM Canon Extender EF 1.4x III +4 more Reply Reply with quote Reply to thread Complain The 300 f/2.8 IS performs better with the Canon EF 1.4x II Extender and the Canon EF 2x II Extender than most if not all other Canon lenses. Adding the 1.4x creates a 420mm f/4.0 IS lens - a very nice focal length and max aperture - and yes, IS still functions with the extenders installed. You are 3.5 years too late and the good advice given at the time contradicts yours. An EF 300/2.8 L gains IQ through either teleconverter. The EF 2x does reduce effectiveness of AF, but it can still deliver keepers. The big superzooms can't deliver competitive IQ and the f6.3 aperture will affect AF as much as the 2x does on the 300/2.8. The Image Stabilizer function cannot be used with the cameras *2 listed below. EF 1.4x III and EF2x III extenders are recommended for use with EOS Digital Cameras. *1: EOS-1D Mark II, EOS-1Ds Mark II, EOS-1D Mark II N, EOS-1D, EOS-1Ds In reply to birdbrain • Mar 8, 2021. For zooms like the 100-500, no. I have owned every version of the EF 100-400 & 70-200 f2.8 and I was near happy with the results of the 2x extenders. The 2x extender can add value on the EF Big Whites, you will loose some IQ but the results are acceptable (and at f8 in most cases). 7IOHE.