Thursday, July 17, 2014

Thunder Mountain Falls II

Quite a long time ago, I posted a photo of the waterfalls by Big Thunder Mountain Railroad, at night, with silky streams cascading around purple and magenta lit rock.  That was at night, though.  The low light means a long exposure is required to get any sort of adequate brightness, and that naturally produces the cotton candy ribbons of water present in a nice, dreamy waterfall photo.

A close-up of the waterfalls by Big Thunder Mountain Railroad.
During the daytime, though, there's much more light abound, so exposing for a long period of time will simply result in a completely white photo.  One way to get around this (and the most commonly used method among professional or habitual photographers) is fit a neutral density filter over the lens.  An ND filter reduces the amount of light that crosses through the lens to the sensor (or film strip), which requires one to either open the aperture or increase the shutter speed to capture the same proper exposure.  In daytime shooting, this allows an exposure of several seconds to still retain the detail of a scene, rather than admit too much light and thus blow up the shot with whiteness.  ND filters come in different types, based on how much light they limit.  A 0.3 filter reduces incoming light be one stop, an 0.6 filter by two stops, 0.9 by three, and so on.  A "stop" is the equivalent of doubling or halving either the shutter speed or the f/stop (aperture).  Since exposure is simply the right combination of the two, you can start to see how the neutral density filter plays its part in affecting exposure.

Without much context, these falls could be from anywhere, really...
I, however, don't actually own an ND filter (it's on my list), so I did not use that method to take these photos. Instead, I set my ISO down to the base of 100 (as low as naturally possible), and cranked my aperture as narrowly as possible, down to f/22.  On a well lit day like this, that meant that my shutter speed could drop to 1/5sec or 1/6sec, more than enough to turn those streams of water into the wispy cotton candy effect.  For relatively rapidly moving water, 1/30sec is usually enough, so anything beyond that starts to get into creative intent.

But I assure you that they were taken at the bridge located next to the final turnaround of the "wildest ride in the wilderness!"
So that's a little lesson in daytime long exposure photography.  Those who take photos regularly probably already know this, but I figured it might be interesting to those who are not as experienced in picture taking!

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