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Thread: Photo imperfections

  1. #1 Photo imperfections 
    Forum Senior Yash's Avatar
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    I wanted to know that why does the objects snapped while moving fast nearer to camera appear to be irregular as compared to the objects far behind.
    As, you can see in this picture, the small pillars far away from camera appear to be regular as compared to one in front of the camera. Is there some kind of Lorentz transformations like length contraction or time dilation, etc ??



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  3. #2  
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    Firstly, the nearer objects are moving faster from your point of view. When the camera is recording it writes the image from the top to the bottom, picture the camera writting lines down the page from top to bottom.

    So if the camera takes the pic in 1/30 of a second it is recording the top of the object first, but at the 30/30 of a second it has moved, so the recording is now done on the bottom of the photo.

    Hope that helps. I presume you aren't moving at relativistic speeds so nothing like that would happen :-)

    *Edit* this is presuming you are using a digital camera, a normal camera might just produce an evenly blurred image - or none at all.


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  4. #3  
    Forum Senior Yash's Avatar
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    Thanks for reply !! So, you mean to say that in the beginning of that irregular/inclined to right small pillar, the time is 1/30 of a second i guess that is .2 sec or 2 millisecond and as the inclination moves downwards the inclination, the recording is taking place at 30/30 of a second or 1 second or 60 milliseconds. All this seems relative to speed of car i guess.
    So, that's the reason of that inclination ??

    Well.. this had even happened with a normal conventional camera too
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    Ok so say you have a solid verticle line and you are passing it rather quickly.

    At time 1/30 you record it at the top, at time 2/30 you record it slightly further down and see that the camera in that 1/30 of a sec has now moved slightly, so it will be recording the light coming from this new position.

    This happens for each 1/30 sec. which then gives it at an angle.

    I know for a standard CCD lens (digital camera) that it is written as an array of pixels very quickly, each line is drawn from left to right and then starts on a second and third line etc all the way down, rather like reading a book!

    I am at odds to explain this for a conventional disposable camera, I would like to have a look at a picture with that if you have it?

    Just to reiterate;

    Time 0 the pillar is at position X (in your window)
    Time 1 the pillar is now at X + 1cm (for example)
    Time 2 the pillar is now at X + 2cm

    During this time your camera is very quickly absorbing information line by line.

    Time 0 the camera is recording lines 1-5, where the pillar is at X
    Time 1 the camera is recording lines 6-10, where the pillar is now at X + 1cm
    and so on, this is kind of an exaggeration but you get the idea.

    This is the only thing I can think of it being, I used to record impacts on the moon and sometimes I would see half an impact if it happened halfway through the image scan in a frame :-). This is to say, lines up to 350 would have been recorded and then an impact flash would occur covering an area between 340-360, so only the latter half would register.
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  6. #5  
    Forum Senior Yash's Avatar
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    All, your assumptions seems to be quite satisfying !! So, i would understand in that case. By, now it seems that i have got the answer to my question.
    Thanks !!
    I'll look for those conventional cameras snapped pictures, because i remember i had one.

    :-D
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  7. #6  
    Forum Professor jrmonroe's Avatar
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    This phenomenon seems due to different effective rotational speeds ... applicable only for the same linear displacement perceived as different rotational speeds due to their different distances.

    Rotational speeds (eg, photos taken from a merry-go-round) would affect all *stationary* objects equally (ie, they'd all appear to lean at the same angle) due to their same *rotational* speeds.

    The slit cameras used for "photo finishes" use a similar technique to produce those funny-looking photos.
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  8. #7  
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    Quote Originally Posted by jrmonroe
    This phenomenon seems due to different effective rotational speeds ... applicable only for the same linear displacement perceived as different rotational speeds due to their different distances.

    Rotational speeds (eg, photos taken from a merry-go-round) would affect all *stationary* objects equally (ie, they'd all appear to lean at the same angle) due to their same *rotational* speeds.
    Good explanation for the apparent velocity differences.

    Also a digital camera on a merry-go-round would curve the foreground in this shape quite a lot: / or \, depending on the direction of travel. Worth noting that even the background would bend at normal speeds in this example. Although I'm not sure what classes as a standard merry-go-round speed :-)
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