Variable ND Filter

[erniethemilk]

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I shoot quite a bit outdoors and have a couple of different standard ND filters I use occasionally. 
 

I was wondering if a variable ND filter would be useful to tame some of the brighter cloud and sky when shooting. 
 

Anyone have hood or bad experience using a variable ND filter? 

[Leica28]

What you need is a graduated ND filter.

[darylgo]

Variable ND are two filters stacked. The convenience is offset with a slight degradation of image quality.  The better quality brand names don’t assure improved image quality, my best variable ND is a Tiffen, a filter brand that is second rate except for their exceptionally good cinema filters.  As a general rule when two filters are stacked there will be a loss of sharpness.  

[jimofnyc]

two polarizers stacked.  Twist one and watch the density change.