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Author Topic: q question of accidental selective focus  (Read 905 times)
Michael West
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« on: January 30, 2010, 09:25:14 PM »
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unaturally selective focus draws fire... [ pun intended ]

I posted this photograph on another  forum in a depth of field  "assignment".

I did not make any notes nor annotations as to how it was taken nor what I might have been aiming for in making it.

The first comment on the photograph was quite unusual in that the poster appeared certain that I had done the "blurring" of the automobile.

The odd fact of the matter is that other than adjusting a few curves and doing some output sharpening  I didnt  "do" anything to the image.

How it happened that one rather tiny area in an image captured form a fair distance ended up in fairly sharp focus while the remainder along the same plane, blurred is beyond my ability to understand.

Its my hope that  there  would be someone "here" who might lend  thier understanding of optical physics so I can understand how such a thing was possible.

Let me add that this was taken at 1/1000 of a second at f1.8, with a 50 mm lens.
Thanks



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Robert Roaldi
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« Reply #1 on: January 30, 2010, 10:16:25 PM »
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If the question is about the rather clear rendering of the reflections in the car's window, it makes to me this way. The car was moving with respect to you, so it is blurred. The tree (or bush) was not moving with respect to you, and neither is its reflection, so it is not blurred.
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Michael West
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« Reply #2 on: January 30, 2010, 11:24:06 PM »
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Quote from: Robert Roaldi
If the question is about the rather clear rendering of the reflections in the car's window, it makes to me this way. The car was moving with respect to you, so it is blurred. The tree (or bush) was not moving with respect to you, and neither is its reflection, so it is not blurred.

Thank you. I sense I had over complicated the "situation".
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Dick Roadnight
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« Reply #3 on: January 31, 2010, 06:23:03 AM »
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Quote from: Robert Roaldi
If the question is about the rather clear rendering of the reflections in the car's window, it makes to me this way. The car was moving with respect to you, so it is blurred. The tree (or bush) was not moving with respect to you, and neither is its reflection, so it is not blurred.
The lamp post is also somewhere near sharp, so the effective distance to the in-focus foliage (via the window) would be similar to the distance from the camera to the lamppost.

If your lens had been miss-mounted, or the body bent, or you used a camera with movements, you could have had the back of the car OOF, the lamppost sharp and the front of the car sharp.
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Colorwave
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« Reply #4 on: January 31, 2010, 11:25:16 AM »
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I was wondering along with you until Robert posted his explanation, but it all makes sense.  Imagine a mirror traveling parallel to the plane of focus.  If it's speed is great enough, relative to the shutter speed, the object reflected in it would be sharp, but the edges of the frame would be blurred.  Nice effect.  Understanding increases your odds of capturing it again without as much luck involved.
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DarkPenguin
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« Reply #5 on: January 31, 2010, 11:37:15 AM »
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Quote from: Colorwave
I was wondering along with you until Robert posted his explanation, but it all makes sense.  Imagine a mirror traveling parallel to the plane of focus.  If it's speed is great enough, relative to the shutter speed, the object reflected in it would be sharp, but the edges of the frame would be blurred.  Nice effect.  Understanding increases your odds of capturing it again without as much luck involved.

If I knew anyone with a cool car I'd be trying this right now.  (Well, probably not right now.)
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