A Coastal Wake-Up Call: Variable ND Filters vs Real-World Light
What I Loved in the Studio, and What Caught Me Out on the Coast
After spending time with the K&F CONCEPT Ultra-Low Reflection Variable ND Filter in the studio, I was genuinely impressed. Long exposures behaved beautifully, reflections were well controlled, and image quality held up exactly as promised.
So naturally, it came with me on holiday. Coastal light, big skies, moving water… the perfect playground for a variable ND, right?
Well. Mostly.
When Reality Hits, Literally Full Sun
Out on the coast, shooting in harsh midday light, I started noticing something I hadn’t seen in the studio at all. At higher ND strengths, especially when working wider, parts of the frame would darken unevenly. In some situations, an unfamiliar “dark cross” or X-pattern started creeping in across the sky.
At first, I assumed something was wrong. A bad copy? A coating issue? User error?
Turns out, it was none of those.
The Important Bit Most of Us Learn the Hard Way
This isn’t a fault with this filter, or with K&F CONCEPT specifically. Apparently, it’s a known physical limitation of variable ND filters, apparently ALL variable ND Filters.
Variable NDs work by stacking two polarising filters and rotating them against each other. At stronger density settings, especially in bright sunlight and with wide or ultra-wide lenses, light enters the filter from multiple angles. Those angles don’t play nicely together, and you end up with uneven polarisation across the frame, which shows up as that dreaded X-pattern.
Subtle X-pattern appearing on images
In the studio, with controlled light and longer focal lengths, this never showed up. Outside, with open skies and brutal contrast, it absolutely did.
Lesson learned.
What Helped (and What Didn’t)
Once I understood what was happening, I could work around it fairly easily.
Things that helped:
Keeping the ND strength just below the maximum range
Avoiding ultra-wide focal lengths when stacking heavy ND
Rotating the filter slowly to find the most even position
Being more selective about when a variable ND was actually the right tool
Things that didn’t:
Pushing it to the absolute ND400 end in full sun
Shooting wide seascapes with big skies and expecting perfect uniformity
This is not unique to this filter. You’ll see the same behaviour with most variable NDs, regardless of brand, once you push them hard enough.
Variable ND vs Fixed ND, Choose Your Weapon
This shoot reminded me why many landscape photographers still swear by fixed ND filters for coastal and seascape work. Fixed NDs don’t rely on polarisation stacking, so they deliver far more consistent exposure across the frame, especially in skies and water.
That doesn’t mean the variable ND suddenly becomes useless. Far from it.
For:
Portraits outdoors
Video work where exposure needs quick adjustment
Controlled compositions without massive skies
Travel and lightweight kits
A variable ND is still incredibly practical.
For:
Bright midday seascapes
Ultra-wide landscapes
Critical long exposures with clean skies
A fixed ND will usually win. I really like the Magnetic Filter kits for this reason
The below images are SOOC
Final Thoughts
I’m still glad I took the K&F CONCEPT Variable ND Filter with me. It performed exactly as physics allows it to perform, which is an important distinction. The issue wasn’t the filter; it was my expectations of what a variable ND can realistically do in extreme outdoor conditions.
If anything, this shoot was a good reminder that no single filter does everything perfectly. Knowing the strengths and limitations of your tools matters just as much as owning them.
And yes, next coastal trip, a fixed ND will be in the bag as well. Consider this experience-earned wisdom, with a side of salty sea air.
