Long exposure landscape photography is very popular nowadays. To do it, you need to fit a strong neutral density (ND) filter in front of your lens to reduce the light level and extend the shutter speed.
My first attempts at long exposure photography were made using a screw-in 10 stop ND filter. I quickly found it inconvenient having to unscrew the filter between each shot to recompose the scene. You could see almost nothing in the viewfinder or in Live View with the filter in place. The exposure was calculated without the filter in place, and then 10 stops were added by counting down the shutter speeds on my fingers! Fortunately, we are all equipped with just the right number of fingers to do this.
The next thing I tried was a variable ND filter which is made up of 2 polarising filters in a single mount. The front one can be...