I invested in a decent ND1000 filter, and found that a little mental arithmetic solved the problem. Thinking in terms of 'stops' can be confusing. The light reduction factor is the critical figure - 4, 8, 16, 32 , 1000, etc. With a digital camera this process is so simple because you can take a picture without the filter first, at your chosen aperture, and note the shutter speed when the image is correctly exposed. So if you used 1/125, with an ND4 filter you will need 4 times the exposure, 1/30. Simple mental arithmetic examples, starting from shutter speed without filter: 1/125, with ND4 = 4/125 = 1/30 (the only mental arithmetic is dividing 125 by 4 to get 30, which is easier that diving 4 by 125 to get 0.03...) 1/125, with ND8 = 8/125 = 1/15 1/125, with ND16 = 16/125 = 1/8 1/125, with ND1000 = 1000/125 = 8 whole seconds 1/60, with ND1000 = 1000/60 = 17 whole seconds (see below) The 2 attached images were taken a few minutes apart with the same F11 aperture and ISO 200 setting. One was taken at 1/60, and one was 17 seconds with my ND1000 filter I used a tripod and cable release, being very careful not to move the camera when attaching the filter. Once the filter is in place the viewfinder is useless. Check you camera's user manual to find out how to ensure that the camera shutter stays open - which may depend on menu settings and the cable release used. The longer the exposure, the less difference 1 or 2 seconds make to the result. I used my wristwatch. A warning - the longer the exposure, the greater the risk of something arriving in shot. In this case my first 2 attempts at 17 seconds were ruined by curious ducks. With a digital camera experimenting, and making mistakes, won't cost you anything but your time. Imagine the fun and expense I had when I tried this 30 years ago with Kodachrome.