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 Post subject: Fast Action Photography
PostPosted: Thu Apr 25, 2013 1:52 pm 
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Joined: Sat Apr 13, 2013 2:28 am
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Location: Richmond Hill, Ontario
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Fast Action Photography

Last summer, I was photographing a whitewater kayak race. I used a 70-300mm zoom lens across its entire range, shooting at F8 in single frame mode. From my vantage point, I was able to follow the racers, set the continuous autofocus, and fire off one or multiple shots in each gate. Except one tricky spot on the river with a fast short drop followed by a haystack. I took a number of shots in that spot, some better than others. When I examined images on my computer screen, I came across the following shot:

Image

I like this image, and it was a sheer luck capturing it. Surely, I wasn't composing and focusing for the hand with paddle. Most likely, I noticed the racer just coming down the chute, focused on him and pressed the shutter. Let's assume that in that particular drop the water moves at 15mph (24km/h), kayak moves relatively to the water at 5 mph (8km/h), so the resulting speed is 20mph (33km/h). If the distance from the top of the drop to the bottom is 5 ft (1.5m), moving at that speed, the kayak can cover 9m in a second, or 5 ft (1.5m) in 165 ms. This corresponds roughly with 100 ms required for a transmission of the image from the retina to the visual cortex, plus another 50 ms to press the shutter. And that explains the confluence of kayak being in the hole just with the hand and paddle visible behind the standing wave and click of the shutter in that very fortunate moment.

As the kayaker cleared the haystack, he was slowed down sufficiently, that I could easily focus on him in that position and make another exposure. If his speed in that moment was around 3-4 mph, he would cover in 165 ms only 1 ft (30cm) which didn't pose any problem for locking the focus or sufficient depth of field at that distance.

Image

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This post is an excerpt from another article, dealing also with some neuroscience information and grizzly bears. The full article can be found at:
http://www.advantica.wordpress.com


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