Review on Enhance and Extend Image Quality with Canon EXT. RF1.4X(N) (4113C002) by Jay Sterns

The RF 1.4x extender is a great product in every way, except that it's quite expensive. I've attached it to a Canon RF 100-500mm lens and everything works fine, so I can't complain about its performance, including IQ, focus, etc. Note that when either of the two extenders (1, 4x and 2x ) is used With the RF 100-500mm or similar zoom lens, the lens can only be enlarged from 300mm to 500mm. If you then want to zoom back, retract the lens to eg 100mm, this is not possible as the lens cannot be retracted more than 300mm (can only be extended/retracted between 300 and 500mm). That 1.4x (or 2x) extension should be nearly perfect for use with prime lenses, not zooms like the RF 100-500mm, unless you're shooting in broad daylight. With this 500mm lens, the aperture without an extender is around f/7.1. You should lose about 1 stop "f" just adding the 1.4x extender. But with Prime RF it should be perfect.