By far the most important accessory you can buy for your professional camera lens is a high quality filter. B+W filters are valued by professional photographers for their exquisite optical quality and fine multicoatings. B+W is a must have for every pro quality lens.
By using this filter, it is possible to use relatively longer shutter speeds while retaining a wide aperture even in bright illumination. This allows for the emphasis of the subject by controlling depth of field or creating motion effect with subject blur. Filter factor is 4.