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08-10-2010, 05:51 PM   #1
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Blur issues at fast shutter speeds

Hi All-

I've been doing some photography shooting from the hip as I walk around in urban areas--when shooting from the hip I tend to get blur at any speed less than 1/200 of a second. My lens is a 21mm so going by the inverse rule I should be able to shoot down to almost 1/20 of a second. I get blur at much higher speeds as mentioned above. I depress the shutter release button to autofocus and then shoot. The AF is set to continuous and the AF point selector dial is set to Auto. Any advice? Am I perhaps just not steady enough? I don't get blur when I pull the camera up and frame the image looking through the viewfinder at the same speeds--I've shot down to 1/60th reliably and sometimes lower.

08-10-2010, 06:43 PM   #2
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My guess would be that when shooting from the hip your AF is not locking in on what you think it is. Especially if you have a shallow depth of field from a lower f stop. When you bring it up to your eye you point it exactly where you want it to be sharp and lock in.
08-10-2010, 07:18 PM   #3
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1) The "inverse rule" applies to FF/135 cams, for 'tolerable' sharpness when you're standing still. In Ansel Adams' THE CAMERA he reports shooting by the rule, a 50mm lens at 1/50 sec handheld, but didn't get a SHARP picture until he got to 1/250 sec. That's a 2+ f-stop change. SR on a Pentax dSLR gives an estimated 2-stop advantage... sometimes. IF YOU'RE STANDING STILL. I'd take another stop, to be safe.

2) DOF ain't the same with FF/135 and HF/135 or APS-C frame sizes. Figure on losing 1+ f-stop over what you'd expect by reading the DOF scale on a FF prime lens. So if the aperture is f/11, you'll get the DOF you'd expect just wide of f/8. I try to fudge by 1.5 stops, to be safe.

3) Let's combine (1) and (2). To get any specific DOF on a Pentax dSLR, go a bit more than 1 stop beyond the scale. To get a sharp picture, boost the shutter speed by at least 2 stops, more if you are in motion (shooting from the hip). For street shooting with my manual Tokina 21/3.8, I'll prefocus to 10 feet at f/8, which (reading off the f/5.6 scale) puts my DOF at ~4.5 feet to infinity. And my shutter is at 1/200, faster if there's much motion. Better would be f/11 at 1/320, prefocus to 2m for DOF of 1m to infinity. And ISO is gonna float...

Last edited by RioRico; 08-10-2010 at 07:51 PM.
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