The 4 x 4" ProStop IRND Long Exposure Kit with Holder from Formatt Hitech is a Joel Tjintjelaar Signature Edition ND filter kit. It includes everything you need to shoot long exposures: three solid neutral density filters, two lens adapters, and a filter holder.
The included filters offer three different degrees of density: 3, 6, and 10 stops. This allows you to control both the exposure time and depth of field in your photos. Without an ND filter, most cameras do not have a shutter speed fast enough to allow you to shoot wide open in bright conditions. By adding an ND filter, you can blur your background and isolate your subject, even under direct sunlight. You can also shoot very long exposures which is useful for landscape and architecture photography. Exposing your shot for a long period can make people, clouds, cars, and other moving objects seemingly disappear from your images.
The filter kit comes with two lens adapters, one 77mm and one 82mm, which fit onto the front of your lens. A filter holder fits onto the front of the adapter and holds up to 3 filters. Also included with this kit is a long exposure technique booklet written by Joel Tjintjelaar, and a long exposure conversion chart, both of which will help you get the most out of your kit.