I was torn between buying (used) an EF 70-200 L and a 70-300 L. The 70-200 could be used with an extender. The 70-300 could not. I reasoned that 200mm extended to 400 would be too much for me to hand-hold, involve carrying the extender around in case I wanted to use it. I'm glad I bought the 70-300. Maintains Metering, Autofocus, and IS. Dust and Water Resistant. Extend the reach of select Canon RF-mount lenses with the Extender RF 2x. This teleconverter magnifies the image by 2x and retains full communication between the lens and camera body, enabling metering, autofocus, and image stabilization as well as the transmission of Exif data. 05-19-2023 01:52 PM. I own a 2X gen II and I have tried a 2X gen III. I think the gen III is marginally better and either will provide acceptable photos with a very sharp prime IF you don't compare the sharpness and contrast of the bare lens to the 2X images. I have used 1.4X converters fairly often and now own an EF 200-400 f4 with the built Fotodiox EOS-2x-AF-Tele Black/Silver Pro Autofocus 2x Teleconverter Compatible with Canon EOS EF Full Frame Lenses and EF / EFs Cameras 3.5 out of 5 stars 309 $155.50 $ 155 . 50 The file is a manual (PDF file) for EXTENDER EF1.4X III / EF2X III. Download drivers, software, firmware and manuals for your Canon product and get access to online technical support resources and troubleshooting. The EF 100-400mm f/4.5-5.6L IS II USM is a lightweight solution for photographers who can only travel with one telephoto lens. Ideal for professionals shooting sports and wildlife, with the 100-400 mm zoom range you can get up close to distant subjects without needing to disturb the scene, and the Zoom Touch Adjustment ring sets the amount of resistance felt when zooming, ideal for working in Enthusiast. Options. 08-06-2023 06:36 AM. From Canon's product page for the RF 1.4X extender: Note: This extender is only compatible with the following RF lenses RF100-400mm F5.6-8 IS USM, RF100-500mm F4.5-7.1 L IS USM, RF400mm F2.8 L IS USM, RF600mm F4 L IS USM, RF600mm F11 IS STM, RF800 F5.6 L IS USM, RF800mm F11 IS STM, RF1200mm F8 L IS USM. Enjoy more zoom on your existing lenses by choosing a Canon extender lens to add to your kit. RF Extender 2x EF Extender 1.4x III While the Canon version of this teleconverter costs $449, Yongnuo is selling its clone for just $180 over on Amazon. Yongnuo YN-2.0X III Teleconverter [Amazon via CanonWatch ] Equipment , News If you used a 1.4x extender then the 100-400 f/4-5.6 becomes a 140-560mm f/5.6-8 lens and that WILL work becuase the wide-open apertures are f/8 or lower for every focal length available. The 2x extender must not be used with any with a focal ratio higher than f/4. XoqTzn.