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Wednesday, August 1, 2007

Extreme Neutral Density


Taking super-long exposures with ND filters can add an artistic component to your photography



Portland Head Light, Maine

Portland Head Light, Maine
Three filters were used to balance and lengthen this morning exposure and give the incoming surf its misty appearance: a Singh-Ray 5-stop solid ND filter, a Singh-Ray Gold-N-Blue color polarizer and a 3-stop continuous grad filter. This continuous filter has no visible edge; it slowly gains in density from clear at the bottom to 3 stops at the filter's top. It works well in situations like this where there's no clean horizon line in which to blend a traditional grad filter. Pentax 645N, Pentax 45mm ƒ/2.8 lens at ƒ/22, Fujichrome Velvia 50 ISO overexposed 1 stop for reciprocity

Practical Considerations

There are several things to consider when trying this extreme exposure technique. If you’re using film, reciprocity failure has to be considered. Film becomes less sensitive to light and colors will shift during exposures of a second or more—the longer the exposure, the more pronounced this effect could be (this isn’t a problem with digital photography). Whatever your calculated exposure time, add 1 to 11/2 stops longer if you’re using film.

With so much ND in front of the lens, composing (or even seeing through the viewfinder) may become difficult. It’s often best to compose the image first, then attach the filters. The ND filter usually goes on first and sits flush to the front of the lens. If using a color polarizer with the ND filter, I’ll thread the polarizer onto the lens first, orient it to the color or polarization I want and then thread the ND filter on (being careful not to let the polarizer rotate). If also using a graduated filter, I’ll attach it last and, because of possible light leakage, I actually tape it flush to the front of the filter stack by its sides. If the front of the filter is getting any direct sunlight, shade it, even if you have to stand there for a half-hour exposure! If the sun is hitting the front of the filters, even at an oblique angle, it still will accumulate and cause flare with such long exposures.

Vignetting can be a problem, especially when you’re using wider-angle lenses. The Singh-Ray Vari-ND and polarizers are available in thin mounts for wide-angle use. This helps, but you’ll probably still get some vignetting if you shoot with more than one filter. Photoshop offers techniques to fix vignetting.

Determining exposure can be tricky, although most D-SLRs do a good job of metering through all the filters and density. The most important thing is to block light from coming in through the rear viewfinder while metering, which skews the reading. Some cameras have a built-in viewfinder curtain for this purpose.

If your camera’s meter will only calculate exposure times below 15 seconds (for many models, that's the low end cutoff), try opening the aperture until you get a correct exposure reading, then calculate the remaining stops to get the maximum exposure length. For example, if you had to open the aperture to ƒ/5.6 before getting a correct exposure reading for a 15-second exposure, you’ll have to count down the remaining stops and exposure times. If, in this example, the minimum aperture your lens had was ƒ/32, that’s five stops from ƒ/5.6 (ƒ/8, ƒ/11, ƒ/16, ƒ/22, ƒ/32). Your exposure time would be eight minutes at ƒ/32 (15 sec. at ƒ/5.6; 30 sec. at ƒ/8; one minute at ƒ/11; two minutes at ƒ/16; four minutes at ƒ/22; and finally, eight minutes at ƒ/32). Set the camera to Bulb and use a cable release. All these long exposures will be running your batteries down very quickly. Be aware of that and have plenty of backup if you’re attempting this technique a lot through the day.

Digital noise also can be a problem with long exposures. Some cameras have built-in noise-reduction features. Use them, even if it takes longer for the file to be written to the card. Or use noise-reduction software, post-shoot, in your RAW converter or Photoshop.

Compositionally, blurred motion is best appreciated when it’s in contrast with something steady and sharp. Whatever your subject in motion is, try to compose it with something that won’t be moving during the exposure. Having a solid stone or tree trunk surrounded by blurred movement can create beautiful visual contrast.

See more of Daryl Benson’s photography at www.darylbenson.com.

Mersey River, Kejimkujik National Park, Nova Scotia, Canada
Clyde Inlet, Baffin Island, Canada
White Point Beach, Nova Scotia, Canada
Mersey River, Kejimkujik National Park, Nova Scotia, Canada
Downstream from a small waterfall as natural foam floats by on the spring current. Canon EOS-1Ds Mark II, Canon EF 24-70mm ƒ/2.8L lens at 60mm, ƒ/22, 10-second exposure, Singh-Ray Vari-ND filter at about 4 stops. The nice thing about shooting digitally with a Vari-ND filter is you can adjust the ND as you shoot until you get the right exposure length to best show motion of the subject. Digitally cropped square
Clyde Inlet, Baffin Island, Canada
Pack ice slowly adrift on the incoming tide, fog and clouds at sunset. Canon EOS-1Ds Mark II, Canon EF 24-70mm ƒ/2.8L lens at 45mm, ƒ/22, 15-minute exposure, Singh-Ray Vari-ND at maximum ND, -8 stops, Singh-Ray Gold-N-Blue color polari
White Point Beach, Nova Scotia, Canada
Incoming surf and cloud pattern. Canon EOS-1Ds Mark II, Canon EF 24-70mm ƒ/2.8L lens at 24mm, ƒ/22, six-second midday exposure, Singh-Ray Vari-ND at about -3 stops, regular polarizing filter. The image was cropped square digitally. It looked better this way, and the cropping got rid of some vignett

Digital noise also can be a problem with long exposures. Some cameras have built-in noise-reduction features. Use them, even if it takes longer for the file to be written to the card. Or use noise-reduction software, post-shoot, in your RAW converter or Photoshop.

Compositionally, blurred motion is best appreciated when it’s in contrast with something steady and sharp. Whatever your subject in motion is, try to compose it with something that won’t be moving during the exposure. Having a solid stone or tree trunk surrounded by blurred movement can create beautiful visual contrast.

See more of Daryl Benson’s photography at www.darylbenson.com.

Resources
B+W (Schneider Optics)
(631) 761-5000
www.schneideroptics.com
Lee Filters
(800) 576-5055
www.leefiltersusa.com
Cokin (OmegaSatter)
(410) 374-3250
www.cokinusa.com
Singh-Ray
(800) 486-5501
www.singh-ray.com

Hoya (THK Photo Products)
(800) 421-1141
www.thkphoto.com

Tiffen
(800) 645-2522
www.tiffen.com




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