don't use ND filters a lot, so I found the idea of a single screw-on filter that could substitute for several fixed ND filters to be appealing. I had read other reviews of this filter, with mixed opinions, so I did my own evaluation in which I was looking primarily at three things: 1. Color cast 2. Artifacts 3. Sharpness I added the last one (sharpness) because of some comments another reviewer had made. I tested the variable ND filter in a studio setting with the camera on a tripod and fixed settings for ISO, white balance, f/stop, and focus. I took images at 6 settings spaced across the range (MIN to MAX) and have included the images here. Here's a summary of my opinion of the performance on these three criteria: 1. Color cast - GOOD. The color balance remained quite uniform over the majority of the range of the filter (see photo). The color cast took a giant step in hue (to blue) at the MAX setting. This would be entirely correctable in any image processing software, but in combination with the other considerations, I don't plan on operating close to the MAX setting. 2. Artifacts - VERY GOOD. I did not encounter any artifacts that resembled color clouds or the dreaded "x". However I didn't push it past its MAX setting, which is where some other reviewer encountered these problems. Didn't expect to use it outside its intended range so I didn't test it there. 3. Sharpness - OK. This was my biggest surprise. I wasn't even intending to check for this, but the degradation in sharpness and contrast over much of the range (with the exception of the lowest values of ND) was notable in the sequence of images I took. (See photo). It was serious enough that I'd be careful using this much higher than the 50% point between MIN and MAX. Perhaps this is just a by-product of using higher ND filters -- I don't know for sure. I don't have any high-end ND filters to compare. The build quality and packaging are good. I particularly like the filter cases that K&F provides, they are easy to use. CONCLUSION: This will be a useful filter for me, but because I know of the limitations and their effect on image quality, I can make some informed decisions about how where to operate this filter and what to expect. Post-processing will certainly improve the image quality and might be needed.