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

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.

"from wikipedia" wrote:

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.

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.

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.:bs:

Although for a flatbed scanner, slowly moving would be enough to cause crazy images.

That's how he tried to explain those pictures of his butt??

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? ;)

Knight f3;524778 wrote:

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.

That would be Matthias Wandel. He amazes me with the stuff he invents.

Wasn't that footer?

Oh, maybe. But I was focusing on the weird digital time/motion capture aspect of it.

No, but I wanted to do that with an old scanner I had. Matthias and I are cut from the same cloth though.

Gravdigr;524781 wrote:

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.

Ooh, ooh! I want one of those, do you know where they sell them?

Gravdigr;524781 wrote:

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.:bs:

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:

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.

no, I have never tried this with my iphone, but I think I might try it now.

I'll see what I can do with my iPhone. Looks like a noble cause.

Wombat;525005 wrote:

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:

So it (the camera)manufactured parts of the prop that don't even exist?:3eye:

Gravdigr;525177 wrote:

So it (the camera)manufactured parts of the prop that don't even exist?:3eye:

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 :)

But how do you get a continuous blade, with two red tips, and no red nose cone in the middle?:confused:

Sundae Girl;524843 wrote:

Ooh, ooh! I want one of those, do you know where they sell them?

Actually...the last time I was camera shopping, they had cameras that claim to fix blotches on your face automatically (after auto finding your face in the frame of course) and other such craziness.

This one makes you skinnier:
http://www.reginalewis.com/2007/09/17/this-camera-makes-you-look-10-pounds-thinner/

lots more examples here and discussions of photon gating and Nyquist frequencies etc.

another example

Moving objects in the same speed/direction as the scanner on a copy machine makes the object look longer. :-)

xoxoxoBruce;525182 wrote:

But how do you get a continuous blade, with two red tips, and no red nose cone in the middle?:confused:

Good question, lets see if we can work it out.

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 :3_eyes:

I'll let you figure out what's happening on the left of the picture yourself :D

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.

But...if the plane was on a treadmill, and the iPhone was trying to take off, would the propeller blades appear at all?

Depends. Is the treadmill on a train approaching the speed of light?

No! But the train did leave the station going west.

Wombat;525180 wrote:

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 :)

I was talking more or less about the part of the prop that bolts to the hub. Where do the hub flanges disappear to, and where does the section of prop that magically appears to connect two seperate sections of prop where there should be hub flanges (for lack of the correct term) appear from?

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.:D

I believe you're seeing the reflection of the blades on the nose.

Anon E Mouse would have worked better


eta.....unless your 1st language es Espanol