Machine direction line film inspection

A method comprising:

• transmitting light from a point light source through a film product, the light refracted at an angle of refraction when passing through and then exiting the film product;
• directing the refracted light to an edge of an opening of an aperture, and blocking, by the edge, a portion of the refracted light from passing through the opening while allowing the remaining portion of the refracted light to pass though the opening of the aperture and be received at an image sensing array when the angle of refraction of the light received at the focal point is an expected angle of refraction;
• capturing, by an image sensing array, an electronic signal corresponding to a variation of a level of light intensity received by the image sensing array for each of a plurality of image areas of the film product, each of the plurality of image areas corresponding to an imaged line on the film product having a direction that is perpendicular to a direction of manufacturing used to manufacture the film product, the variations in level of light intensity received by the image sensing array resulting from variations in the angle of refraction of the light exiting the film product in the plurality of image areas of the film product;
• and
• analyzing the image to detect the presence of one or more machine direction lines in the film product.

A method of calibrating a film product inspection system comprising:

• transmitting, from a point light source, without passing the light through a film product, the light to a reflective surface at an angle that corresponds to an expected angle of refraction, the light reflected at an angle of refraction equal to an expected angle of refraction the light would be refracted at if the light passed through and then exited a film product to generate a refracted light exiting the film at the expected angle of refraction;
• directing, by a reflective surface and without passing the reflected light through a film product, the light to a focal point behind a lens;
• positioning an edge at the focal point so that a predetermined portion of the reflected light is blocked by the edge, and a remaining portion of the reflected light passes the edge through an opening adjacent to the edge;
• and
• adjusting the position of the edge so that the remaining portion of the reflected light passing the edge through the opening in the aperture is received at an image sensing array in a level that generates an electronic signal in image sensing array corresponding to a predetermined level of light intensity.