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Old December 11th, 2007, 09:12 AM   #31
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Quote:
Originally Posted by Mooho Bae View Post
But, still, I can't imagine the geometric distortion explained by your small aperture, ray tracing model. IMO, the diffraction will be the key in this issue.
Without a diagram I can't explain it any further, but diffraction effects tend to get worse as the aperture gets smaller, whereas what I'm talking about should get more pronounced as the iris gets larger - and being a night scene I'd expect the iris to be wide open.

If you're still curious, PM me an address I can e-mail a sketch to.
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Old December 11th, 2007, 09:27 AM   #32
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Quote:
Originally Posted by David Heath View Post
Without a diagram I can't explain it any further, but diffraction effects tend to get worse as the aperture gets smaller, whereas what I'm talking about should get more pronounced as the iris gets larger - and being a night scene I'd expect the iris to be wide open.

If you're still curious, PM me an address I can e-mail a sketch to.
David, My point is somewhat different.. Kaku's clip clearly shows (and I can reproduce with my XH A1 any time,) that the pixels very near the obstacle in the image actually moves.(That made the distortion.) The ray theory can not explain this phenominon IMO.
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Old December 11th, 2007, 10:00 AM   #33
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Originally Posted by Mooho Bae View Post
The ray theory can not explain this phenominon IMO.
I think it can if you think of half the lens being blocked off, so it's effective centre is shifted a quarter diameter, with consequent effects on the image.

Another way of thinking of it is to think of what happens to the circle of confusion of an out of focus point source as you obstruct half the lens. One half goes away, so the nett result is the remainder is smaller and it's AVERAGE position is shifted relative to the unobstructed image.
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Old December 11th, 2007, 10:10 AM   #34
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I think the effect is not totally dissimilar to crescent shadows during a solar eclipse, in which case the edge of the moon causes a lensing effect on sunlight.
http://www.astrospace.co.uk/gallery/...-crescents.jpg

The bokeh is essentially distorted back in to (or towards) focus as it bends around the edge of the foreground object, atleast thats how I like to think about it.

Particles... Waves... magic?

;0)
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Old December 11th, 2007, 10:22 AM   #35
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What effect exactly are you all looking at? The only thing I see is a brief flash which could be attributed to the taxi turning slightly and having something reflect off its side - a few frames later it's clear the taxi is moving.
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Old December 11th, 2007, 10:24 AM   #36
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Originally Posted by David Heath View Post
I think it can if you think of half the lens being blocked off, so it's effective centre is shifted a quarter diameter, with consequent effects on the image.

Another way of thinking of it is to think of what happens to the circle of confusion of an out of focus point source as you obstruct half the lens. One half goes away, so the nett result is the remainder is smaller and it's AVERAGE position is shifted relative to the unobstructed image.
David, if you do not consider the diffraction, even if a half(or any amount ) of the aperture blocked, the traced ray falls at the same position in the imaging plaine. And, IMO, The 'circle of confusion' can be explained by the diffraction.

I guess you and I have both very similar concept, but I also guess that you and me are trying to explain the same thing in a different way.

One more thing I wan't to say is that the DOF and the aperture relationship is also based on the diffraction. The 'ray tracing theory' has nothing to say to this relationship.
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Old December 11th, 2007, 10:48 AM   #37
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Originally Posted by Kevin Shaw View Post
What effect exactly are you all looking at?
Although one frame doesn't fully demonstrate the distortion, atleast it helps pin point the mid-point about which you need to scrub the play head to see the warping in action. It looks a bit odd out of context but plays fine as part of the whole scene, the EX1 is doing nothing 'wrong' here.

Hope you don't mind me posting the grab Kaku !?
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What do you think this is?  Rolling shutter issue?-taxi-plate.jpg  
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Old December 11th, 2007, 11:06 AM   #38
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Thanks Dave - yes, it's the difference between this frame and the one before that best demonstrates what's being referred to. Going back a frame, the unobscured "89" is still out of focus, but the now partly obscured "39" is sharper and darker.
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Old December 11th, 2007, 11:15 AM   #39
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The sharpening effect on the 39 (partial bokeh) seems to me to be caused by the foreground 'man with bag' object as it moves past, almost as a halo effect. I'd call this diffraction = light bending around the edge of an object.
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Old December 11th, 2007, 05:56 PM   #40
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My bad!

David and Serena, I'm sorry, I was wrong.

I re-tested it with my cams, and I realized that the image at the focus does not move. Only the images out-of-focus moves with the obstacle moving.

Maybe the 'diffraction model' can precisely describe these, but now I agree with the David's explanation. It's enough to explain all these. Thanks.
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Old December 11th, 2007, 08:15 PM   #41
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Posted this on another thread but applicable here. imho

I used to use an A1U and it had "Rolling Shutter"

I looked for the footage but was not able to find it.

Simulate the footage by selecting the highest shutter speed, 1/10,000 for A1U. Drive down the interstate in the fast lane at or just above the speed limit, 75MPH or so. Frame the oncoming traffic fast lane perpendicular to the flow of traffic. A box truck or semi-trailer would be noticeably slanted. I found it disturbing.

Would be nice to see someone with an EX1 do this trick. Maybe shooting out the window of the driver's side backseat would be wise.
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