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Old Oct 28, 2007, 2:12 PM   #1
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Last weekend I took some photos at a local Dressage show that my wife was competing in. This was not a nationally recognized show, so some of the rules don't apply. For instance, at recognized shows, the horses' manes must be braided, but not at local shows.

Another rule for recognized shows is that the riders must wear formal riding attire. That is, they must wear black helmets, white shirts or blouses, black riding jackets, white breeches, and black boots. At local shows, they can wear formal riding attire, and even braid their horse's mane, but they don't have to.

I took thousands of photos with my KM5D/Beercan, Continuous AF / Spot AF Area / Continuous Advance, and they all turned out well, except for the photos of one competitor, the only one wearing proper riding attire. Every single photo of her was out of focus. Every photo of every other competitor was perfectly focused.

I expect that I'll be taking photos at recognized shows at sometimein the future, and I'd like to find out what caused this, and fix it, before that time rolls around. Is it possible that the combination of the proper riding attire and the black saddle and white saddle pad under the bright sunlight created too much contrast for the autofocus system?



A100% crop from the approximate center of the frame.



Might aCircular Polarizing Filter reduce the glare and improve the accuracy of the AF System?
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Old Oct 28, 2007, 3:00 PM   #2
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My best guess, and it's only a guess, is that the little bit of CA visible in the cropped photo, was enough to fool the phase detection of the auto focus, and it picked the fence rail in the b/g. The white areas being too hot probably contributed some as well. Likely you would need a little negative EV for these conditions. Polarizer might help, but you will lose light, and your SS could drop lower than you want.

A less bright day would probably not have given you any problem at all. Order some clouds for the next shoot.:-)

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Old Oct 28, 2007, 5:41 PM   #3
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Actually, the above shot has these exposure values:

Exposure Time = 1/640"
F Number = F5.6
ISO Speed Ratings = 200

I think I can afford to lose a stop or two.

And my wife is competing in another local Dressage show next Sunday. I'll see what I can do about getting some clouds. :-)
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Old Oct 28, 2007, 9:05 PM   #4
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I'm sure your wife will appreciate that!

From the other post you mentioned that you were using spot focus. Is it possible that you consistently place the focus point in the bright white area? I wonder if wide area focus mode mightwork better.
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Old Oct 28, 2007, 9:21 PM   #5
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FrankD wrote:
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From the other post you mentioned that you were using spot focus. Is it possible that you consistently place the focus point in the bright white area? I wonder if wide area focus mode mightwork better.
You may be right (though that would probably be extraordinarily accurate framing on my part.) I've already ordered a CP filter for my Beercan, but I'll try the Wide AF area too.
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