82mm Ultra-Low Reflection Variable ND Lens Filter, ND2-400 (1-9 Stop) HD Adjustable Neutral Density Filter with 28 Multi-Layer Coatings for Camera Lenses - Nano-X Series

SKU: KF01.3157

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The reflectivity is 0.15%. 
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Yes, but if you want to stack a larger filter (e.g. 52mm to 55mm), you will also need to stack a larger lens cap. 
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No, this model is infinitely adjustable. 
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This filter frame is 7.4mm thick. The picture is suitable for 19mm filter frame; the video is suitable for 17mm filter frame. 
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It is not suitable for lens hoods because the front end of this filter is one diameter larger.