Canon Extenders only fit a limited range of EF lenses – essentially L-series primes with a focal length of 135mm or more and L-series zooms with a minimum focal length of 70mm. Because extender-compatible lenses vary in their native optical capabilities, the suitability of the results captured with extenders differs significantly. That said, when you can't get any closer and can't use a lens with a longer native focal length, using the 2x extender makes sense. Canon RF extenders are relatively expensive. The Canon FE 2x extender is a small and light addition to your kit, a moderate hit on your wallet, and in terms of versatility and capability increase, it is worth having in the gear bag. Canon's very serious about the optics; look at the huge curved rear element: Canon RF 2× extender. AF performance and image quality and sharpness have been superb with the TC in place. With lens elements protruding from the front of the primary lens barrel, Canon and most other brand extenders do not fit behind a non-compatible lens. With an extender mounted behind it, a lens's native minimum focus distance remains the same, and the maximum magnification spec is increased by the extender's magnification factor. The difference in framing (angle of view) is quite noticeable. Canon provides a 1-year limited warranty. Top Rated Gear: Canon Extender EF 2x III (Tele Extender) - U.S.A. MFR: 4410B002. From a functionality standpoint, extenders change little. Low light levels increase the autofocus challenge, and with the narrower aperture presented by the 2x extender, increased focus hunting in such conditions should be expected. The Extender EF 2X III from Canon is designed for select Canon EF mount L-series telephoto lenses. Autofocus performance can be reduced with an extender in use, but the with and without 2x difference is generally not big under good light conditions. The mounted measurements are 2.8 x 1.6" (71.2 x 39.3mm), shorter than Canon EF 2x III Extender's 2.83 x 2.07" (72 x 52.7mm) dimensions. TC2a.src = 'https://media.the-digital-picture.com/Images/Other/Canon-RF-600mm-F11-IS-STM-Lens/Focal-Lengths/840mm.jpg' TC3 = new Image(700,276) Canon shares: Renting is fast and easy. Decreased sharpness (resolution and contrast) is, historically, especially noticeable with a 2x mounted, and the RF 2x degradation is I'll bullet the list for quick reading and then will discuss the points. TC1a = new Image(656, 439) TC2a = new Image(656, 439) The Canon extenders have a protective rubber surface around the front element to protect the extender and the lens from misalignment while mounting. There’s no such thing as a free lunch though! However, Canon recommends that the New FD 300mm f/2.8L to be used with the Extender FD 2X-B instead. It has had very little use and there are no marks, scratches or fungus on it or in it. The RF 2x Extender comes with the Canon Lens Case LP811, a reasonable quality drawstring pouch that is only padded on the bottom. //End comment tag.-->, Bringing you this site is my full-time job (typically 60-80 hours per week). The RF 2x minimally increases the blur size of the native lens's lateral CA and increases barrel distortion slightly (slightly more than the RF 1.4x), nicely offsetting the pincushion distortion common at long telephoto focal lengths.