Instruct: Classify a given review into positive or negative sentiment.
Query: Great addition to my EF 70-200 L f/4 !!!

This high quality extender is a great addition to my Canon EF 70-200 L f/4 !! With a top-notch build quality and a tough, weather resistant design equal to that of their highly respected line of "L" lenses, Canon has produced a great product for its unbeatable zoom lens !! Although the 2X extender renders the A/F function useless on many Canon cameras, I found this to be a Very small drawback overall ( I prefer to manually focus under many of my shooting conditions). This extender is more suited for a low f/number lens due to the 2-stop change in brightness, but it is still VERY effective with my f/4 in normal lighting. A lightweight and fairly inexpensive way to double your focal length, while maintaining the incredible optical quality of the main lens...My backpack will always contain my 2X and 1.4X extenders !!