The difference is clear.
The PROND1000 has a 10-stop light reduction equal to a ND optical density of 3.0.
The ACCU-ND technology in the Hoya PROND filters yields a truly neutral color balance that will not add any noticeable color-cast to your images. The Hoya PROND series is aimed at the still photography and HDSLR video markets. The series provides 9 filters from two stop to 10 stop light reduction.
The Metallic ACCU-ND coating on the PROND filters do not color shift as you move from one density to the next, a common problem with other series of neutral density filters. Now you can set your white balance once and have the same color balance even if you need to change filters due to changes in lighting, or for creative effect.
The PROND filters use Hoya’s exclusive clear optical glass that has a metallic ACCU-ND coating front and back to create the neutral density affect.
Neutral density filters are designed to reduce the amount of light entering your camera lens and should not have any other effect on the image. Reducing the amount of light allows for the use of wider apertures or slower shutter speeds for creative and dramatic effect in bright lighting conditions.
The HOYA PROND 1000 is an extremely dark neutral density filter with a filter factor 1000. This filter factor converts to a 10 stops reduction on the amount of light entering the lens. With this extreme filter motion is greatly blurred or depending on the speed some moving subjects will disappear altogether. With a ND filter as strong as the PROND 1000 shutter speeds as slow as 16 seconds or more are possible in daylight.