Slot at the rear of the shade is for 3x3 in. (75x75mm) gel filters in Gel Filter Holder 40495. Shade does not attach directly to the lens, lens mount adapter rings must be used. Adapter ring 40320 for use with 50mm front mount lenses. Adapter ring 40344 for use with 60mm front mount lenses. Adapter ring 40339 for use with 63mm front mount lenses. This shade can be used with a filter, Softar or Proxar on the lens.