This is the variable ND filter from Fotasy.
It's difficult to find such filters at 46mm, which is a common filter size for Micro Four Thirds lens, such as the Olympus 12mm f/2, Panasonic 14mm f/2.5 lens, 20mm f/1.7 lens, 25mm f/1.4 lens and the 45mm f/2.8 lens.
It should be more useful for the Panasonic 20mm and 25mm since they are quite fast to begin with.
This is multi-coated to reduce lens flare and reflection.
The ND filter can rotate from ND2 to ND400. That's 8 stops which is good enough for long exposure shots, i.e for waterfalls, rivers, waves. Typically for normal still shots, ND4 or ND8 is sufficient.
The manufacturer states that the ND filter works best for lens under 200mm.
The main advantage of this filter is you can keep it on all the time. When you don't need it, you can just rotate it down to ND2.
The price is really attractive compared to other brands. But the main draw is the 46mm filter size.
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The Fotasy 46mm Adjustable Fader ND Filter Neutral Density (ND2 - ND400) Multi-Coated is available at: