Physics/optics question of the day. (Challenger-related)

[Recharger]

Ok, rather than a blatant hijack, I thought I'd start a new thread regarding the pics posted about the new Challenger.  [regardless of whether or not anyone else finds this interesting.]  We see in these pictures that the wheels are blurry, relative to the car.



Typical of automobile photography right?  Right.  But look at the spokes on the wheels.  The spacing of the spokes seems irregular, and two of the spokes seem to be blurred/distorted more than the other spokes on the SAME wheel.



So the question of the day is....Why would that be?  Why are some spokes blurred differently than the others on the same wheel?   A free web-beer  to whoever offers up the most correct answer first....  Or to whoever offers up a better theory than the (quite possibly incorrect) one in my mind....

[68chrgrwife]

I believe it is just the angle of the spokes in the wheel.  I am probably wrong...I get a kick out of watching the commericials and watching the wheels "go backwards". 

[Brock Samson]

  it's the wind blowing them..... of course... 

[my73charger]

Those are a new test wheel that when up to speed actually "flex" thus causing better performance and in the end better gas mileage.......

[runningman]

Physics and Optics...my favorite topics....

My theory: I would guess that it is an optical illusion brought about by the speed of the spokes interacting with the shutter of the camera.
The forward spokes are dropping down, relative to the shutter of the camera, which is also dropping down at likely the same speed.
Therefore the spokes travel with the shutter. They're not captured in any particular position. In photo-terminology, it's called "panning".
As you can see, the background is slightly blurry, and it is also an overcast day. This means in order to get the shot, a compromise was made with regards to shutter speed. I would guess it was shot at 1/60th of a second, at possibly an ISO of 100.
The rear spokes of the wheel are seen as going upwards, against the movement of the shutter, so they are closer to their actual respective positions.

Make any sense?

That's exactly what I was going to say 

[Charger_Fan]

Physics and Optics...my favorite topics....

My theory: I would guess that it is an optical illusion brought about by the speed of the spokes interacting with the shutter of the camera.
The forward spokes are dropping down, relative to the shutter of the camera, which is also dropping down at likely the same speed.
Therefore the spokes travel with the shutter. They're not captured in any particular position. In photo-terminology, it's called "panning".
As you can see, the background is slightly blurry, and it is also an overcast day. This means in order to get the shot, a compromise was made with regards to shutter speed. I would guess it was shot at 1/60th of a second, at possibly an ISO of 100.
The rear spokes of the wheel are seen as going upwards, against the movement of the shutter, so they are closer to their actual respective positions.

Make any sense?

That's exactly what I was going to say 

Me too, but I was gonna word it more like..."cameras on 'ludes should not take pics".

[PocketThunder]

Physics and Optics...my favorite topics....

My theory: I would guess that it is an optical illusion brought about by the speed of the spokes interacting with the shutter of the camera.
The forward spokes are dropping down, relative to the shutter of the camera, which is also dropping down at likely the same speed.
Therefore the spokes travel with the shutter. They're not captured in any particular position. In photo-terminology, it's called "panning".
As you can see, the background is slightly blurry, and it is also an overcast day. This means in order to get the shot, a compromise was made with regards to shutter speed. I would guess it was shot at 1/60th of a second, at possibly an ISO of 100.
The rear spokes of the wheel are seen as going upwards, against the movement of the shutter, so they are closer to their actual respective positions.

Make any sense?

That's exactly what I was going to say 

       

[Charger1973]

Those are a new test wheel that when up to speed actually "flex" thus causing better performance and in the end better gas mileage.......

Elastomeric wheels!!! 

[Rocky]

Nah, they left bigger spaces on the front of the wheels so they could get more air to cool the brakes.  "Better living through engineering". 

[Recharger]

Actually, Musicman, I was just about to award the    to Magnumcharger for getting the answer.  What's your theory, or at least, the other half of it that 68chargrwife missed?   

[Recharger]

   I had a long reply written up and lost the whole thing when my internet went out.     Here's a shorter version, I'm not sure how much I left out so hopefully it makes some sense...


  Good answer Musicman!  Though, referring to your previous quote, I'd have to say Magnumcharger had the closest answer.  (no offense chrgrwife)

Your answer is pretty much exactly the theory I came up with last night after looking at the pictures.   As you said, from the point of the view of the camera, the lower spokes are moving "back", against the motion of the car while the upper spokes are moving "forward" with the motion of the car.  As a result, the lower spokes have a higher relative velocity as compared to the body of the car.  Therefore, they would be tougher for the camera to focus on and they seem blurrier than the other spokes.

However, something still didn't seem quite right with the picture, which is why I posted the question here for more input & theories.     This relative speed theory would suggest that the distortion would be split top to bottom along the horizontal axis of the wheels, being more pronounced in the lower spokes than the top spokes.  But the picture seems to show that the distortion is split more along the vertical axis, with the spokes on the front half of each wheel looking blurrier than the rear half.   

That's why, after reading Magnumcharger's answer, I'm starting to think he's closer to the actual cause of what we're seeing.  I was trying relate the speed & direction of the spokes to the body of the car, the main focus of the picture.  I hadn't considered the speed and direction of the shutter itself which, if it does operate vertically, explains the front-to-back split in distortion.  The front spokes move down 'with' the motion of the shutter, and the rear spokes move 'up' against it.  Therefore the front spokes move with a slower velocity relative to the shutter.   In effect, it's like the rear spokes are being photographed with a higher shutter speed.  Higher shutter speed = less blurring.

The other aspect to take into consideration is the angular motion of the spokes.  With each rotation of the wheel, the outer edge of the spoke (near the rim) is covering more distance than the inner portion of the spoke in the same amount of time.  This means the linear velocity of the spokes is constantly increasing as you move away from the axle.  As a result the outer edges of the spokes are moving at a faster speed and the resulting blurring & distortion is more pronounced near the rim.  Isn't physics fun!


So, it looks like Magnumcharger gets the    (your choice)
And Musicman gets a runner up                (domestic only)

[Charger1973]

Those are a new test wheel that when up to speed actually "flex" thus causing better performance and in the end better gas mileage.......

Elastomeric wheels!!! 

I still like my answer the best.   

[RD]

My theory is that I dont give a shit and the car looks F%%$#% cool driving on the road finally!  Physics, shutter speed, cameras.. hell, what I wanna know is:

WHERE IS THE DAMN BURNOUT PICTURE!







hehe

[Brock Samson]

o.k.   that was yestidday,..

  today i wanna know why the grill is all 1970 mod lookin?.. 

thanks for the weirded out photo 500...   

[Brock Samson]

Sorry guys... you asked...
By the way, it's not the wheel spoke movement in relation to the car body, it's the wheel spokes radial movement in relation to horizontal image blurr. The wheel is turning at a much faster rate than the forward movement of the vehicle. Also... Camera shutters do not operate up or down, or side to side... this would result in one side of the image receiving more exposure than the other. Most camera shutters are complex, multisegmented devices, which expose the image area in a series of instances. I know the earth looks flat, and it can easily be argued that it is flat, but the bottom line is, the earth is sort of roundish... that's all folks.

     WTF did he just say?. 

[Recharger]

o.k.   that was yestidday,..

  today i wanna know why the grill is all 1970 mod lookin?.. 

thanks for the weirded out photo 500...   

All I know is that it's called moire effect.  It results when photographing tight grid patterns, or a series of tight parallel lines like in house siding or charger grille teeth.  Why?  no idea....