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12-04-2010, 03:21 PM   #1
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K-5: behavior with flash in Av

Bit the bullet and got my K-5 this week. Amazing camera, coming from a k200d it's a whole new world to me.

I noticed one thing I haven't seen on the k200d: with flash mounted and a zoom lens (notably the Sigma 17-70) in Av mode, the camera automatically increases the shutter speed as the lens is zoomed to a greater focal length, and decreases it as the lens is zoomed out.

As if it somehow tries to compensate for camera shake - somewhat odd with flash and SR in place, though.

Yet so far, the camera simply leaves me in awe, and such little details only improve on the general picture

12-04-2010, 11:28 PM   #2
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What shutter speed is it choosing? I can't be sure, but it seems like the K-5 tries to keep the shutter speed no slower than 1/2 the focal length. That would require the shake reduction to "handle" about 1.5 stops. Even with flash, this is a pretty good practice, since ambient light can still contribute to the exposure at slow shutter speeds.
12-05-2010, 12:34 PM   #3
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On 17mm, it's 1/50. On 70mm, it's 1/125.
12-07-2010, 03:03 AM   #4
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The Sigma 17-70 opens at f:2.8 at 17mm and at f:4 at 70mm that's why the shutter speed changes...

12-07-2010, 06:12 AM   #5
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indeed it chooses a shutter speed according to the 1/focal length rule of thumb to avoid camera shake, since flash is being used anyway. The k7 does the same thing. To turn that feature off, you need to set the camera flash setting to slow sync.
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