A light blocking sheet having a central axis includes a central hole and a plurality of inner extended portions. The central axis passes through the central hole, which is enclosed by a hole inner surface. The hole inner surface has a first corresponding circle and a second corresponding circle, wherein a diameter of the first corresponding circle is greater than a diameter of the second corresponding circle. The inner extended portions are adjacent to and surround the central hole, wherein each of the inner extended portions is extended and tapered from the first corresponding circle towards the second corresponding circle and includes an inner surface, and the inner surface includes a line pair. The line pair includes two line sections, wherein one end of one line section thereof and one end of the other line section thereof are towards the second corresponding circle and approach to each other.