After doing my homework, I found that the Canon 77 mm circular polarizing filter offered the best value - good quality at a reasonable price. However, I was somewhat chagrined when I attempted to afix a Canon 77 mm lens cap to the filter. I would not fit. It seems that there are not enough screw threads on the outside of the filter to allow the lens cap to seat properly. Literally, the lens cap hangs by a thread. Now, when I uses the lens, I must be very careful that the lens cap doesn't pop off. Very frustrating and a clear example of poor engineering. Canon, what were you thinking?