The A Series filter holder and filters fit all 35mm SLR camera lenses with 36 thru 62mm diameter filter threads and Hasselblad (R) mount. A Series Filters require the use of the A Series Filter Holder. Cokin Graduated filters: The dense (color) area covers less than half of the filter but can be adjusted vertically and by rotation. These filters allow for variable effects depending on the distance of the filter from the lens, its position in the holder and the density of the filter used. (123) darker blue.