Why does a variable ND filter cause an X-pattern and uneven darkening on a wide-angle lens?
Asked 2/14/2013
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I’m using an inexpensive variable ND2–ND400 filter on a full-frame camera with a 17–40mm lens. At stronger settings, especially around 17mm, my images show poor results with uneven darkening and a visible cross/X pattern. If I back off the filter, the image improves, but then the effect seems much weaker.
Is this normal behavior for variable ND filters, particularly on wide-angle lenses? Do I need to avoid the maximum setting, zoom in, or is the filter likely defective?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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Yes, that cross effect is common with all variable neutral density filters, especially with very wide angle lenses (12-17mm). You'll have to do some combination of zooming out or backing off the maximum density.
I did some experimenting with a mid-range filter in the blog : Marumi ND2-400 Variable ND Filter Review. The effect was almost non-existent at 17mm with that filter, but noticeable at max density at 12mm.
The filter I tested did give roughly 7-8 stops. It was roughly an ND2 at its minimum. You should certainly get better than ND8 from it.
Originally by user4191. Source · Licensed CC BY-SA 4.0
user4191
13y ago
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This is normal behavior for variable ND filters, not necessarily a defect. Variable NDs commonly produce a dark X/cross pattern and uneven shading as you approach their strongest settings, and the problem is more noticeable on very wide-angle lenses.
At 17mm on full frame, you’re in a range where this can show up easily, especially with cheaper filters. In practice, you usually need to back off from the maximum setting and/or use a longer focal length to avoid the artifact.
A variable ND should still give more than an ND8 effect overall; a typical ND2–ND400 model often delivers around 7–8 stops near its stronger usable range. So the filter isn’t limited to ND8, but its highest marked setting may not be cleanly usable on a wide lens.
In short: yes, back off the maximum density, and expect better results when zoomed in rather than at the widest end.
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