Buying an ND filter

10Jul08

I’ve always liked to capture motion in my photos. Like the motion of people in my Vatican museum spiral staircase photo, or long exposure of waterfall, I like them all.

Vatican spiral staircase Rapids IIb

There’s something special about capturing perceived movement in still images — a sense of dynamism.

Now to achieve the blur associated with the motion, I need a slow shutter speed, which means that either natural light is low and hence less light is getting to the sensors, or I artificially limit the amount of light getting through. There’s not much I can do with the former, but I can control the latter.

One way to limit light is with the use of a neutral density (ND) filter. I already have a circular polarizer in my arsenal, which can act as an ND filter as well since it limits light transmission due to the way it works. On checking, I found that it’s cutting the light by 1.7 stops. That means that if I normally shoot at a shutter speed of 1/100s, with the polarizer, the speed increases to about 1/30s or so. Not bad, but still not slow enough for a variety of subjects. So to get even slower speeds, I need an ND filter.

If I could swing it, I’d get a Vario-ND filter by Singh-Ray. But at about $350 for a 77mm filter, I don’t think so! There are instructions online to build it yourself with a circular and a linear polarizer, but that’s not what I want to do. To give myself the widest range of light reduction, I’m thinking of an ND filter that reduces light transmission by 4 stops. So basically, between my polarizer and the ND filter, I’ll have 1.7 stops, 4 stops, or 5.7 stops (if I stack the filters) reduction in light. With the filters stacked, that 1/100s can be increased to about a 1/2s exposure. This will come in handy with beach and wave shots when I visit Newport, Oregon shortly.

Currently, I’m looking at the Tiffen High Transmission ND 1.2 filter, which gives the 4 stop light reduction I’m seeking.

If there are some other filters I should consider, or if there’s a better way to do this, drop me a note.

Happy Friday, folks!

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