|Top image, with no ND Filter|
"Singh-Ray Mor-Slo filters are a great way to get really long exposures. What I like most about them is that they don’t produce images with the strong blue or magenta color casts that other very high-density filters do, and the filtration is completely uniform. The Mor-Slo filters come in two basic designs. The ring-mount versions screw onto the front of your lens, while the flat 4-inch square versions require a rectangular filter holder. Each of these filter types offers the serious field photographer certain advantages.
"For those who travel, the ring-mount filters are probably the easiest to deal with. Because they are ring-mounted, they are sturdy and you don’t need to carry any additional adapters in order to use them. They also permit the use of lens hoods in the field, which can be very important on sunny days. On the downside, the screw-in filters may sometimes vignette with very wide-angle lenses, and if you wear gloves in cool weather it can be cumbersome to put the filters on and off your lens. I point this out because with extreme filtration (10+ stops), you’ll need to compose, focus, and meter the scene with the filter removed.
"The square Mor-Slo filters are identical in composition to the ring-mounted ones, the only difference is that you use them with a filter holder. The 10-stop Mor-Slo has a foam rubber gasket to prevent light leaks. I personally use the square (4-inch) filters for my field work for several reasons. First, they are large enough to use with my widest lenses (16-35mm zoom) without vignetting. That’s great for getting those dramatic skies with moving clouds. Second, because I’m using a filter holder, I can quickly and easily remove the adapter from the lens in the field to compose and focus without having to unscrew anything. Lastly, because most filter holders let you use more than one filter, I can stack a 5-stop Mor-Slo or use a graduated ND filter when capturing my shots. The drawback of the square filters is that you can’t use your lens hood while shooting, and they are somewhat less sturdy than the ring-mounted variety.
"No matter what filter you choose for long exposures, however, there are a few tips to keep in mind to get photos with impact. First, keep in mind the whole point of a long exposure. We use long exposures to blur motion. Sometimes this is to smooth out a body of water, but other times it’s to create a sense of motion from moving objects. A long exposure of a static subject isn’t any different than a short exposure of it. Find what’s moving, and use different amounts of filtration to get the desired motion effect. For fast-moving subjects, you won’t need much, sometimes 5-stops is enough. For slow-moving subjects, or bright conditions, you’ll need at least 10-stops of ND, and maybe even more. That’s why I carry both 10 and 5-stop Mor-Slo filters.
"With a combined 15-stops of ND, you can quickly find yourself getting exposures of five or more minutes. That can be really long! But here’s the nice thing about having all those stops of ND: you get more degrees of creative freedom. With 15-stops of ND, you don’t need to use Lo-1 ISO on your camera. You can shoot at base ISO and get a cleaner result. You also aren’t forced to stop down to f/22 to get a long exposure. That’s really great for avoiding diffraction softness, or for using shallow depth of field as a creative tool. With my Nikon D800e, I prefer to shoot between f/8 and f/11 for maximum sharpness. The 15-stops of ND filtration lets me do that and still get reasonably long exposures." (Editor's note: Singh-Ray now offers 15-stop Mor-Slo filters.)
In 2004, Jason established Luminescence of Nature Photography, dedicated to outdoor photography and photographic education. In addition to writing, he conducts field photography workshops and software training classes for photographers around the world. He is also the author of numerous eBooks on digital photography which are available through his site.
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