An image sensor includes a plurality of light detecting elements. The removable panels can zip up into place to divide the bag into a central space and end spaces, or can be unzipped and rolled up to create one large space or two sections. As a result, the amount of control by the aperture is determined so that the amount of control by the aperture does not exceed the controllable range, and an ND filter, which corresponds to or is approximate to the amount of control of reduced light which was obtained by subtracting the amount of control by the aperture from the total amount of control, is placed on an optical path. The first interpolymer and the second interpolymer can be polymerized in a single reactor or they can be polymerized in separate reactors operated in parallel or series.