Beware of uneven lighting on wide angle lenses
I'm just a novice photographer, with limited experience using filters. That being said, I know my way around exposure settings and fairly literate with the technical specs of my cameras.I wanted to take some smooth pictures of waterfalls and saw this variable ND filter with good reviews. On the item description page, there's plenty of warnings to make sure you buy the right filter thread size for your camera, which seems pretty obvious. However, they don't mention that this ND filter is poorly suited to wide angle lenses. For reference, I had paired this filter with a Zeiss Touit E 12mm f/2.8 mounted on a Sony a6500.After coming back from vacation, I realized that many shots I took with the filter mounted had pretty poor light uniformity. I did notice while taking the photos that rotating past a certain point produced noticeable unevenness, but the effect was less/not noticeable when I turned the ND down. However, upon checking the images on a computer monitor, it was obvious that the brightness is not uniform.I asked the seller about the issue and copied/pasted their response below:"Darkness is a common issue with wide angle lenses and variable ND filters. Physics limit the capabilities of variable ND filters on wide angle lenses. When you enter the edge of the max range,the darkness may appear on your image. Because you are using it beyond its capability according to the laws of optical physics,which will inevitably cause this phenomenon. could you try to turn down the degree until the black fade away?"So I guess I'll chalk this up to inexperience on my end. Still, I'm docking 2 stars because it's not documented anywhere on the item page which focal lengths are supported, which can lead to some mislead some buyers. Also, it's not really feasible to tell if there is a slight amount of uneven brightness while taking the shot or previewing in camera. Thus, you can end up with a bunch of bad shots that you wouldn't know about until you get back to a monitor.