Kenko Variable Neutral Density Filter

For my birthday this year I treated myself to the Kenko Variable Neutral Density filter (link here), not an inexpensive item, but quite useful. A variable ND filter is one with two layers of polarizing film and one rotates the  top layer to obtain the desired level of density for a shot. These variable NDF filers are quite handy as it allows one to carry just one filter rather than a stack of filters and can be used for a wide range of applications, as the Kenko link above demonstrates.  The Kenko filter advertises a range between 1 and 8.5 stops of adjustment.I have long recognized the value of carrying some neutral density filters beyond just the use for blurring the motion of flowing water. Because I have developed  a particular fondness for shooting lighthouses, I am quite often in their presence in bright sun light with the white of the lighthouse tower quite a bright spot. I have learned that one can use a ND filter to contract the light range and eliminate some of the highlight clipping that would otherwise occur in this type of scene as the Kenko's web site demonstrates.So, when Sing-Ray introduced their variable neutral density filter back in 2005, I jumped on the band wagon. Carrying one NDF was a lot easier than 3 or 4. Besides, one eliminates the need of stacking filters together to obtain the desired effect thus solving the problem of potential vignetting. However, I quickly became discouraged with Sing-Ray's variable NDF filter. I discovered it created a color shift that seemed to increase as one increased its density. As a result, it became a tool little used. To be fair, Sing-Ray now has a newer design and I have no experience with their present variable NDF filter nor do I know if they resolved the color shift I encountered in their initial version.While reading the January, 2012 issue of Outdoor Photographer, I noticed an ad for Kenko's Variable ND filter that promised no color shift. So I thought I would give it a try, purchasing it from a vendor where I knew I could return the filter if it proved to not meet Kenko's claims. I must say that Kenko's Variable ND filter met all of their claims and then some.

• First of all, the Kenko VNDF is about 1/2 the thickness of the old Sing-Ray filter. (and I suspect of the new one as well). It is about the same thickness of a regular polarizing  filter, a big deal for putting in on a wide angle lens.
• Secondly, it is nicely marked on the side so that one can tell where they are at. (Sing-Ray's new VNDF does have similar markings)
• Third, I like the range that Kenko provides. It has an effective range from ND2.5 to ND450. However, my experience is that at ND450 it is effectively not usable as cross-like color variations start to occur. The VNDF that Sing-Ray now sells goes from 2 to 8 stops, virtually the same range.
• In the full range of densities tested I could not detect and color shift.

In short, I highly recommend the Kenko Variable Neutral Density filter. It will greatly help one extend the light for blurring motion, it is small and easily stored in a camera bag. Because it has little to no effect on color, it can be used for a wide range of applications for images and video.Here are some of my test images:The first image is without any filter.Its settings are ISO 50, f/11 at 1/25.Second image is with the Kenko filter on at its minimum setting, which reduces the light 1 stop. One can notice a very slight color change in this image that remains constant.I have not adjusted the colors on these images at all. All of the images are with the same adjustments, exposure, sharpening, as well as black point and white point adjustments.This image is at the maximum point that Kenko recommends (the maximum point of their markings). This is 4 stops slower than the original; ISO 50, f/11 at 0.6 sec.The next image represents just about 7 stops slower and just about as far as one can go before encountering the effect of the cross-like color variation that is predominant in the next image.Pretty much the maximum adjustment that one can go is at 9 stopsHere is the first image from the "old" Sing-Ray VNDF filter. This is at its lowest setting. Notice the substantial color shift.Next image is with the "old" Sing-Ray filter at about 6 2/3 stops;and the last one is with the "old" Sing-Ray VNDF filter at about 7 1/2 stops.