Thank you Gigatron. It helps a bit, the sprite it's not quite opaque but almost (If I increase the alpha value the blurred region looks messy).
I have another question. About a few default distorsion effects: Warp, Water, Water Background.
Can they be modify in such a way that when the camera moves, their speed is not affected ?
I mean, if the camera is fixed it animates properly. But if the camera is moving the property values are affected (increased).