67mm ND2-32 Filters Brass Frame Adjustable HD Ultra-Thin 36-Layer Anti-Reflection Green Film Nano-Xcel Pro Series

SKU: KF01.1996

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Answer: 7.4mm 
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Brass, CNC molded for both hardness and flexibility, smooth and durable installation. 
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It has 36 Multi-layers which is K&F Concept's exclusive coating technology. 
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Lens caps can be installed, but you need to add 1 size of lens cap. For example, if you purchase the filter 67mm, you will need to install a 72mm lens cap. 
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No hood can be installed. This filter has a larger aperture and larger frame diameter to avoid dark corners. 
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All adjustable ND filters will have this problem, the larger the focal length used the less the impact of the cross dark shadow. There will be obvious cross-hatching and vignetting in the large stop of light reduction, and the dark shadow will disappear naturally if you continue to rotate, which is a physical phenomenon, not a product problem. 
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By design we can avoid the use of the filter in non-wide angle lens will not have dark corners, if your focal length is less than 24mm may still return to produce.