Soft Grad –These filters are typically for scenes with a very dynamic horizon, like landscapes with trees or high mountains. Soft grads are the most forgiving and easiest for beginners to use.
Hard Grad - These filters are typically for scenes with a straight and uniform horizon, like the sea. If a hard grad is not positioned perfectly, it will be clearly noticeable in the image as a dark line below the horizon or a bright line above it. We advise that beginners stick to soft and medium grads.
Medium Grad – Medium grads are a newer product that most manufacturers only released in 2016/2017. Many photographers often found hard grads too hard and soft grads too soft and thus it was obvious that something in between was necessary. It is also the perfect solution for photographers that don’t want to commit to a hard or soft grad. Not everyone can afford to buy the full range of these filters and the medium grads are an excellent new compromise.
Reverse Grad – These filters serve a very niche, but useful purpose. When shooting into a bright sunset/sunrise, the brightest area is right on the horizon and then the sky darkens towards the top. When using a normal graduated ND, it will result in a correctly exposed horizon, but the top part of the sky will be far too dark. A Reverse Grad also has a clear lower half, but it is darkest in the middle and then gets lighter towards the top. This allows one to more accurately balance those exposures that are brightest on the horizon.
Focal Length Factor - A longer focal length softens the graduation as the image is captured through a smaller portion of the filter. If you shoot a lot of landscapes with your 24-70 or 70-200, then you'll need hard grads.