The Sandmarc Motion Pro Variable filter can be used for both filming and photography. For me, it excels at one more than the other, not because of quality, but because of ease of use.
If you haven't heard of Sandmarc before, they make various types of filters including hybrid and anamorphic for iPhones, drones, and GoPro action cameras. They are easily portable filters in a variety of formats that produce quality images for the content creator or budding filmmaker. They also produce the Hybrid Pro (a polarizer and ND system) and the Motion Pro Variable ND.
The Motion Pro variable filter is a screw-on filter that produces great results for both your photography and your filmmaking. Available in various thread sizes 58mm, 67mm, 77mm, 82mm and with an ultra-slim profile of just 7.2mm, the filter makes a great addition to your kit bag, not simply because of the size but because of the quality of image you get when using such a versatile filter.
Filming on the Go
I tried the filter for both filmmaking and photography, but it really excelled for me in the filmmaking department, and that's quite simply due to the smoothness of the glide through the stops. It works great for long-exposure stills photography, so if you want to just use it for that, you'll get the images you expect from a variable ND8-ND64 (3-6 stops). For filming, though, it works a treat, and I've been using it on the Z 6II to get exactly what I need filming in ever-changing lighting conditions.
I can't overemphasize the smoothness of the glide through the ND's range. For me, that makes it so very useful when filming moving shots that require you to adjust the exposure throughout. The smoothness means you don't notice the change in the final shot, unlike some I have tried. I'm not a filmmaker by any means, so I cannot say if there are better options out there. For me, however, this has been a great addition to the gear and accessories I currently use when creating videos.
The Build Quality
The filter is made from industrial-grade aluminum and weighs a mere 28 g at the largest size of 82mm. The outer adjusting ring has knurling to allow for grip when adjusting. The multicoated cinema-grade glass is resilient. I've had two mishaps and the glass is still scratch-free, so that's a bonus. There's also no x-bar cross vignetting when adjusting the ND. The filter comes in a compact pouch to keep it clean and safe when not in use.
What I Liked
For myself, the quality of the images didn't depreciate when using the filter as it can with some cheaper filters. There is no tightness or looseness when you rotate the filter, just a smooth flow. The glass is resilient. I've dropped the filter twice now, and it landed face down on rocks the first time and received no scratches whatsoever. The second time, it landed on the aluminum edge and received only the slightest of indentations that don't affect the use in any way at all.
What I Didn't Like
This seems like a small point, as I use it for filmmaking and not photography, but the knurling on the filter should be just slightly more pronounced. I found that when filming in colder climates and with my hands being cold, my fingers would now and again slip off the knurled area when adjusting on the move. That's no problem at all when just doing a static shoot, and it's set to whatever ND I wanted, but I thought this was worth mentioning.
As previously mentioned, if you are a filmmaker, I don't think you would go wrong with this filter at all. Great quality of glass produces images that you would expect from a variable ND filter. I've found it handy when filming in ever-changing lighting conditions; that's the main use for me. But it works as expected for stills shooting. It's a very compact size that easily slips into your pocket if you just want a carry about variable ND when out walking with your camera. You can purchase yours here.