ND filters are fantastic pieces of kit for a number of applications, but there is a powerful use for them that sometimes gets overlooked through misconceptions. In this video, see visual examples of exactly what an ND filter can do for you.
When I was first introduced to ND filters, I distinctly remember thinking they were for landscapes, or darker filters like the ND32 were for long exposures. In fact, I bought some for that very purpose, without truly understanding the value they can add elsewhere.
This changed on a fashion shoot some years back where I had a model in front of the ruins of a castle at golden hour. I liked the scene as a whole, but the sun was at the wrong angle for a shot I had in mind and the castle became a little overwhelming in the final frame. That is, it drew the eye away from my model, which is the last thing I wanted. So, I knew I could lower my aperture — perhaps even wide open — and get the best of both worlds. However, I had to overcome the age-old problem: if I lower my aperture, I will have to use High-Speed Sync (HSS) on my flash, which I didn't have the option of. If I used just the max sync speed, even at ISO 100, the image was blown out. So, I added an ND filter to take a couple of stops of light out of the image.
In this video, see visual examples of exactly that and how ND filters can be useful in your portraiture when you're battling against bright natural light and the balancing of your own equipment.