The marumi dhg achromatic macro 330 +3 filter is of the same quality as a professional ‘top filter’ for a fraction of the price. the dhg series filters are made up of a special coating to counteract unwanted reflections, a matte black metal rim and black glass edges to minimize internal reflections. the filter has at the front a screw profile to mount lens/filter accessories. Marumi dhg achromatic macro 330 +3 filter possibilities The marumi dhg achromatic macro 330 +3 filter is an achromatic conversion lens and is ideal for close up photography. the achromatic macro lens shortens the focal length, enabling you to capture an object/subject close up while maintaining a sharp focus on the object. by using a close up filter, you will be able to photograph an object from a shorter distance than your lens is normally able to. The minimum focal distance of the marumi dhg achromatic macro 330 +3 filter differs depending on the camera lens. the general formula and an application thereof is as follows: X: (d* x + 1) Where x equals the minimal focal point of your camera lens and d equals the diopter (or strength) of your close up filter. The diopter of your close up filter is multiplied by the minimal focal point of your camera lens. one is added to this number and the minimal focal point of your lens is divided by this final number. for example: 0.55: (3* 0.55 + 1) = 0.55: (1.65 + 1) = 0.55: 2.65 = 0.21cm Thus, a lens with a minimal focal point of 55cm used in conjunction with a close up filter of +3 would increase the minimal focal point to 21cm.