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Jan 21, 2009: Digital Weird
The guy that took this picture says;
| The cheap CMOS sensor of an iPhone does not expose the whole thing at once, it scans from left to right. If you take a picture of something that moves very fast (like an airplane prop) you can get some crazy pictures out of it since each column represents a slightly different time. |
Anybody with an iPhone seen this happen?
Link
Scriveyn Wednesday Jan 21 02:09 AM
There are classic (non-digital) SLR cameras which have a slit moving across the film (focal plane shutter) rather than a central shutter. I dimly remember reading about strange effects that can be produced by these, so I looked it up on wikipedia (see quote below). - So this not an effect new or restricted to digi-cams.
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Originally Posted by from wikipedia
Distortion of fast-moving objects: although no part of the film is exposed for longer than the time set on the dial, one edge of the film is exposed an appreciable time after the other, so that a horizontally moving shutter will, for example, elongate or shorten the image of a car speeding in the same or the opposite direction to the shutter movement. For an example of such distortions see this image taken with a vertically traveling focal-plane shutter, showing extreme distortion of fast-moving helicopter rotor blades.
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Knight f3 Wednesday Jan 21 03:24 AM
Seen it
The cellar had already documented this phenomenon. As I recall, a guy had modified a flatbed scanner to work as a digital camera and he would get similar weirdness in his photos of moving objects.
Although for a flatbed scanner, slowly moving would be enough to cause crazy images.
Still looks cool though.
Gravdigr Wednesday Jan 21 04:52 AM
Cool how the camera even manufactured the parts of the prop that wouldn't be visible, at all. You know, covered by the nose cone. Yeah, that's cool, a camera that automatically photoshops your pics for ya. Awesome.
SPUCK Wednesday Jan 21 05:55 AM
| Although for a flatbed scanner, slowly moving would be enough to cause crazy images. |
sweetwater Wednesday Jan 21 07:39 AM
It's new to me and now I want to borrow someone's iPhone to see if I can replicate the effect. Let me borrow yours, OK? 
glatt Wednesday Jan 21 08:33 AM
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Originally Posted by Knight f3
a guy had modified a flatbed scanner to work as a digital camera and he would get similar weirdness in his photos of moving objects.
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Undertoad Wednesday Jan 21 08:53 AM
Wasn't that footer?
glatt Wednesday Jan 21 09:56 AM
Oh, maybe. But I was focusing on the weird digital time/motion capture aspect of it.
footfootfoot Wednesday Jan 21 10:21 AM
No, but I wanted to do that with an old scanner I had. Matthias and I are cut from the same cloth though.
Sundae Wednesday Jan 21 10:40 AM
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Originally Posted by Gravdigr
Cool how the camera even manufactured the parts of the prop that wouldn't be visible, at all. You know, covered by the nose cone. Yeah, that's cool, a camera that automatically photoshops your pics for ya. Awesome.
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Wombat Wednesday Jan 21 05:15 PM
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Originally Posted by Gravdigr
Cool how the camera even manufactured the parts of the prop that wouldn't be visible, at all. You know, covered by the nose cone. Yeah, that's cool, a camera that automatically photoshops your pics for ya. Awesome.
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Here are some pics of stationary propellers so you can see how the blades come out the side of the nose cone:
newtimer Wednesday Jan 21 07:07 PM
You stood a few feet in front of a spinning propeller just to take a photo? And the wheels aren't chocked, either. Sounds like a Darwin award waiting to happen.
By the way, where is Bruce now? He hasn't said anything since he posted the picture.
Bruce? Hello? Let us know you're alright.
Agent-G Wednesday Jan 21 07:31 PM
no, I have never tried this with my iphone, but I think I might try it now.
Elspode Wednesday Jan 21 10:53 PM
I'll see what I can do with my iPhone. Looks like a noble cause.
Gravdigr Wednesday Jan 21 11:43 PM
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Originally Posted by Wombat
Nose cones don't cover the propeller blades. The blades come out the side of the nose cone. Which makes the photo plausibly real, not photoshopped.
Here are some pics of stationary propellers so you can see how the blades come out the side of the nose cone: |
Wombat Thursday Jan 22 12:36 AM
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Originally Posted by Gravdigr
So it (the camera)manufactured parts of the prop that don't even exist?
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xoxoxoBruce Thursday Jan 22 12:58 AM
But how do you get a continuous blade, with two red tips, and no red nose cone in the middle?
Razzmatazz13 Thursday Jan 22 01:44 AM
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Originally Posted by Sundae Girl
Ooh, ooh! I want one of those, do you know where they sell them?
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This one makes you skinnier:
http://www.reginalewis.com/2007/09/1...ounds-thinner/
barefoot serpent Thursday Jan 22 01:17 PM
lots more examples here and discussions of photon gating and Nyquist frequencies etc.
barefoot serpent Thursday Jan 22 01:23 PM
another example
spudcon Thursday Jan 22 04:45 PM
Moving objects in the same speed/direction as the scanner on a copy machine makes the object look longer. :-)
Wombat Thursday Jan 22 04:59 PM
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Originally Posted by xoxoxoBruce
But how do you get a continuous blade, with two red tips, and no red nose cone in the middle?
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Looking at the pitch of the blades at the top-center of the picture (where there is least distortion), I think the propeller must be spinning clockwise as we look at it. That way the blades are pushing air towards the back of the plane.
If the shutter is a vertical slit that moves from right to left as we look at the picture, I think that explains the effect we see....
In the top-center of the picture, the blades and shutter pass in opposite directions when both are close to vertical, so we see straightish blades.
On the right of the picture, the tip of the blade passes the shutter first, then as the blade swings down through horizontal the shutter has moved slightly further left so we see the middle of the blade slightly further left than we saw the tip, and finally as the blade approaches the bottom of its swing the fast-moving blade tip overtakes the slower-moving shutter, and so we see the tip again slightly further to the left. The result: it looks like a double-tipped blade floating unattached in the air
I'll let you figure out what's happening on the left of the picture yourself
HungLikeJesus Thursday Jan 22 07:17 PM
I agree. If the shutter is moving left to right, the propeller has to be spinning clockwise (from our POV). Because you can see the root of the propeller in the top but not the bottom, the smallest relative velocity between the shutter and propeller must occur there - so they're moving in the same direction at the top and the opposite direction at the bottom.
Elspode Thursday Jan 22 07:29 PM
But...if the plane was on a treadmill, and the iPhone was trying to take off, would the propeller blades appear at all?
Griff Thursday Jan 22 08:06 PM
Depends. Is the treadmill on a train approaching the speed of light?
SPUCK Friday Jan 23 04:19 AM
No! But the train did leave the station going west.
Gravdigr Thursday Jan 29 07:33 AM
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Originally Posted by Wombat
I can't see any parts of the prop that don't exist, so I'm not sure what you are referring to. To me, every part of the picture looks consistent with a focal-plane shutter exposure of a moving object. Yes it is weird, but I think it's genuine
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And, to clarify, I'm not saying the pix are actually photoshopped. (I just thought the bs flag was cool) Just perpetuating the oft repeated cellar mantra. I've seen these type pix before, I just can't wrap my fragile little mind around the idea.
Anon. Y. Mouse Saturday Oct 3 04:42 PM
I believe you're seeing the reflection of the blades on the nose.
lumberjim Saturday Oct 3 10:00 PM
Anon E Mouse would have worked better
eta.....unless your 1st language es Espanol
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