KF Concept and PolarPro both make screw-on variable ND filters that let you darken a scene by turning a ring, so you can use slower shutter speeds or wider apertures in bright light. The two brands differ mainly in range, build details and how they are positioned, so check the exact stop range and thread sizes on each maker’s page. We have not used these filters ourselves, so this guide focuses on stable traits and how to choose.
How a Variable ND Works
A variable ND filter combines two polarizing layers. Rotating the front ring changes how much light passes through, which gives you a smooth range of darkness instead of fixed steps. This is convenient for video, where you want to hold a shutter speed near twice the frame rate and still use a wide aperture outdoors.
What to Compare
- Stop range: some variable NDs cover a lighter range, others go much darker. Match it to your use, such as moving water in daylight versus general video.
- Thread size: choose the size that matches your lens front, or buy a larger filter with step-up rings.
- Frame and ring: look for a low-profile frame if you shoot wide, and a ring that turns smoothly with clear markings.
- Stops of color shift: variable NDs can add a slight color cast. Ask whether the maker describes its color neutrality.
- Hard stops: a built-in stop at the end of the range helps you avoid dark cross-shaped patterns.
Common Problems and Fixes
- Dark X pattern: this can appear when a variable ND is turned toward its maximum, especially on wide lenses. Back the ring off until it disappears.
- Uneven sky: polarizing effects can vary across the frame at certain angles. Reframe or reduce the density.
- Soft corners: thicker filters can vignette on very wide lenses. Test at your widest focal length.
- Color cast: set a custom white balance or correct it in editing.
| Use case | What matters most |
|---|---|
| Video outdoors | Smooth ring, stop range, neutral color |
| Waterfalls and streams | Strong maximum density |
| Wide landscapes | Slim frame, lack of dark pattern |
FAQ
Is a variable ND better than fixed ND filters?
It is more flexible and faster to adjust, while fixed filters are often more consistent in color and have no pattern risk. Many photographers who shoot long exposures prefer fixed filters, and many video shooters prefer variable.
Should I buy one big filter for all my lenses?
You can, using step-up rings. Buy for your largest lens thread. Be aware that a large filter on a small lens can add bulk.
The Short Version
Both brands offer screw-on variable ND filters, so decide on stop range, thread size, frame depth and color behavior. Confirm those details on each maker’s page, and keep the ring away from its darkest end to avoid unwanted patterns.
