Neutral Density Filter Test

When I decided to purchase neutral density filters, I first looked at variable neutral density filters. However reviews on the web indicated that they are prone to color issues as well as various distortions under certain circumstances. Therefore I decided to acquire fixed neutral density filters instead. Reviewed here are fixed 3-stop and 6-stop X4 82 mm ND filters that I bought which are manufactured by Breakthrough Photography. Their claim to fame is the use of Schott glass that is multicoated on each side with 16 layers of a color neutral Nano-coating claimed to increase transmission while reducing reflections and making them easier to clean. Their other claim to fame is the use of machined brass for their frame. This results in less jamming than filters using aluminum frames.

The filter’s performance was tested by photographing a Macbeth Color Checker using a Canon 5D Mark IV camera fitted with a Canon EF 24-70 mm F- 2.8 LII USM lens set to 50 mm at F/5.6. An initial frame was exposed with no filter on the lens. Then, in turn, both the 3-stop and 6-stop filters were mounted and the exposure time increased by 3 stops in 6 stops accordingly. The resulting images were opened in camera raw in Photoshop CC 2018 and measured in the L*ab color mode using the Eyedropper tool.

For those not familiar with the L*ab color mode, L* is the luminance channel which runs from 0 (Black) to 100 (Luminous White), while the “a” channel is the Green-Magenta axis, and “b” is the Blue-Yellow axis. Both the “a” and “b” run from -128 to + 128 with “0” being neutral. Thus a negative a-channel reading indicates green while a positive a-channel reading indicates magenta. The further away you go from zero towards either extreme indicates a higher degree of color saturation. Similarly, a negative “b” indicates blue, while a positive “b” indicates yellow. So for our purposes here, the ideal filter should have both the “a” and “b” values as close to zero as possible for both the unfiltered and filtered values, while the L* values should match each other as closely as possible. The results show below, for the 6 patches measured, that while the color balance of the tested ND filters did not appear to be totally neutral, it was virtually identical to the unfiltered values. The L values are similarly virtually identical. Thus these two filters perform as precisely claimed providing 3 and 6 stops of attenuation with no significantly measurable or perceptible affect on color balance.

Neutral Density Filter Test Results:

ND Filter Test Results

 

RGB Visual Comparison:

Comparison of ND Filters

So these filters do indeed appear to function as advertised. And not to be dismissed is their 25 year guarantee, provided that you register them.

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