First test
PRICE: FROM£39.99
SWAINS.CO.UK
K&F Concept Variable NDX 2-32 adjustable ND filter
A variable ND filter lets you easily control how much light gets to the sensor, so has huge potential for both still photography and video
How much light reaches the sensor (or film) fundamentally impacts on what camera settings are available to you and therefore the final result, which is why neutral density filters are so important. With them you can set the right aperture and/or shutter speed to achieve the effect you want without altering the light’s colour. Most ND filters have a preset value, thus absorbing specific amounts of light, but the downside of this is that you might need a selection of NDs in the bag to help get the result you’ve imagined. Enter the variable ND filter, one which lets you fine-tune the amount of light entering the lens within its working range. K&F’s filter tested here has a 2x to 32x filter factor, which means a 1EV to 5EV working range – an unfiltered shutter speed of 1/125sec becomes 1/4sec with this filter used at its strongest setting. Variable ND filters comprise two circular polarisers, one in front of the other in a rotating frame. Rotate the frame and one polariser moves, while the other stays put and the
amount of light blocked alters. A potential problem of some variable NDs is that an X pattern is visible as the filter nears its maximum strength. So in this test I wanted to see if this was an issue, as well as the filter’s performance in terms of optical quality, colour performance and light absorption. The filter frame is made from aircraft-grade aluminium and the rotating mount is smooth and fluid but with good resistance, so it stays put once adjusted. A simple scale, with the smallest dot marked by MIN, represents a filter factor of 2x, and the largest dot is 32x or 5EV. In my test, this basic scale proved perfectly accurate. I took test shots indoors and out. Indoors, I used a test chart with a constant light source, a Rotolight Neo 2, with a colour temperature output of 5560K. Outdoors, I shot mid-afternoon on a bright day at the coast and inland on an overcast day too. Indoors and out I used a Nikon D810 in manual exposure mode and took shots using auto white-balance and the camera’s Kelvin presets
SPECS
› Prices and availability Tested here: 77mm at £53.99. Other sizes available 52mm£39.99, 58mm£42.99, 62mm£44.59, 67mm£47.99 and 72mm£51.99 › ND range 2-32x, 1EV to 5EV › Material Optical glass › Features Scratch resistant, Nanotec multi layer anti- reflective coating, Nano-X coating for waterproof, scratch- resistant and oil resistant qualities. Ultra-slim rim and rotating mount made from aviation-quality aluminium. › Contact swains.co.uk
ABOVE Filter density is marked on the rotating section of the filter – MIN is for 2x, and the largest dot represents 5EV. Handily, the filter only rotates between these two limits
– 4550K through to 6250K. I also bracketed exposures +/-0.3EV. My tests demonstrated that K&F’s filter is an impressive and very capable performer. The 2-32x range was exactly as advertised and the basic scale on the filter rim was spot on; colour accuracy using the camera’s auto white-balance was good too. There was a minor colour shift towards warm at the higher filter factors, Optical and physical performance were first rate too. Viewing pictures shot with and without the filter, I couldn't see the filter having any impact on detail or sharpness, and resistance to flare was good too. And as for the previously mentioned dreaded X that can afflict variable NDs, no sign of that at all - probably because it was only 5EV. The filter is slim, about 8mm deep not including the screw thread, and the filter’s generous diameter means I didn’t see any vignetting with the 20mm and 24mm wide- angles I used. As for its physical qualities, the Nano coating made it easy to clean finger grease off the filter with no smearing, and no permanent residue resulted from water droplets left to evaporate. WC
Verdict The K&FVariable NDX 2-32 adjustable ND filter is a top-quality product. It does exactly what it says it will do – reduce light by 1EV to 5EV without any unevenness – and it does so with no discernible impact on the lens’s optical performance.With the 77mm version tested here available at £53.99, it is very good value for money too. PROS Build quality, optical performance, colour quality, no serious white-balance variance in the ND2- 32 range, no cross polarising issues CONS Nothing
No filter, AWB
5EV, AWB
5EV, 4760K
5EV, 5560K
ABOVE This variable ND produced a slight warm cast at its stronger settings but this wasn't a problem and easily corrected in editing.With preset Kelvin settings, 4760K gave slightly cool shots and 5560K was slightly warm but both were perfectly good
Issue 74 | Photography News 45
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