After I had with a blocking filter another brand sharpness problems, I have this replaced by the Canon Protect filter and lo and behold, the sharpness problem was gone. I am very happy with it.
Because a filter in front of the lens at least makes me a peace of mind when I think of the contamination of the lens from dust grains and flying particles that need to remove it. So I think it's imperative before my lenses to wear protective filter
