This teleconverter provides 1.4x image magnification at the cost of 1 f-stop of aperture. Very little image degradation occurs when used with telephoto prime lenses, and it is useable with Canon’s L-series telephoto zooms (however, you may lose the ability to autofocus.).
Please Note: The Canon 1.4x will not fit on wide angle or standard zooms, wide angle primes or third party lenses.