The Marumi Macro Achro 330 + 3 Filter DHG 49 mm is an achromatic close-up lens made from extra strong glass. The lens features a multi-coating that makes it water, scratch, and dirt resistant. It shortens the focal length, allowing you to get closer to the subject. Ideal for close-up shots and product photography. The specially designed ring prevents unwanted reflections. Compared to non-achromatic lenses (standard macro filters), this DHG lens increases sharpness and reveals more details in challenging subjects like glass and jewelry. No extension of exposure time is necessary. The filter on the front has a screw profile for mounting lens or filter accessories. The strength of an achromatic lens is measured in diopters, in this case +3. You can calculate how to reduce the minimum focal length with a specific macro or close-up filter using the following formula: X: (D * X + 1). X is the minimum focal length of the lens in meters and D is the diopter.