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B Frame as time (30 fps camera)

  1. Feb 29, 2016 #1
    So if i take a picture (for example) 30 fps camera. So my question is that: is the time in the picture 1 s \ 30 fps or is it just 0? (May be very stupid question)
     
  2. jcsd
  3. Feb 29, 2016 #2

    berkeman

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    With film motion picture cameras, the film has to be advanced between frames. The shutter is closed while the film advances. It them opens for a time to expose the frame, and then closes to advance the film again. (EDIT -- Source = wikipedia)

    The simplest cameras would open the shutter for about half of the frame time, and close it for the other half to advance the film. More advanced cameras may have more control over the shutter opening time.

    Are you asking more about film cameras, or solid-state cameras? :smile:
     
  4. Feb 29, 2016 #3
    Well i got this idea just 30 minutes ago when i got my gopro back. so film camera
     
  5. Feb 29, 2016 #4
    Sorry forgot the quote^^
     
  6. Feb 29, 2016 #5

    A.T.

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    That's a solid state digital camera. It doesn't use a film. The exposure time can vary, for example depend on the amount of available light.
     
  7. Feb 29, 2016 #6

    davenn

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    Lets go back to the start
    you said take a picture ... then say 30fps
    that's a contradiction ... did you take a single pic with some arbitrary setting or a bit of video @ 30fps ?

    the exposure time of a single image will be whatever you set it to be
    the exposure time for the video is fixed, each frame is 1/30 th of a sec


    Dave
     
  8. Feb 29, 2016 #7

    davenn

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    indeed

    if used for taking still frames, not for video mode


    Dave
     
  9. Feb 29, 2016 #8

    A.T.

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  10. Feb 29, 2016 #9

    davenn

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  11. Feb 29, 2016 #10

    russ_watters

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    The frame rate does, however, set the maximum possible shutter speed.

    For my astrophotos, I often set a frame rate based on the shutter speed. For Jupiter, I can set 30fps or even 60fps, with very short exposures. For Saturn (dimmer, further away), I'll set it lower (perhaps 7.5 or 15 fps) and set somewhat longer shutter speeds.
     
  12. Mar 1, 2016 #11

    A.T.

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    Note that not every camera gives you direct control of shutter speed in video mode. But you can easily see, that the full frame duration is not always used for exposure: Film a very fast object (which smears out) and overlay two subsequent frames: The combined smear of two frames usually has a gap, indicating the time of non exposure.
     
  13. Mar 1, 2016 #12
    I took a video with 30 fps and thank you
     
  14. Mar 1, 2016 #13

    sophiecentaur

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    The blurring of your personal movement perception acts on top of the effects of blurring with long camera exposure times.
    The maximum exposure time will be 1/30s but you will get better motion portrayal if a shutter is used, to reduce the exposure time of each frame. Ideal time samples are short impulses and not a blurred frame image, which is why low light sequences may not look so good as well lit sequences. Frame rate conversion is also much better if a shutter is used to get short frame samples. A shutter shutter time is also essential if you want to use a wide lens aperture (for shallow focussing effects) in bright conditions.
    Modern sensors perform much better than film and short shutter times are, I believe, more available to digital filming than for chemical filming because ISO numbers can be extremely high in modern sensors.
     
  15. Mar 1, 2016 #14

    A.T.

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    Here is what a fast spinning propeller can look like in two consecutive frames of a video overlaid. Note that the smeared green & red markings are on one blade only, so the two green arcs represent the same object, in two consecutive frames:

    ?temp_hash=5c703719998c514746463077beda4f22.png

    As you see the exposure time (time captured in each picture) is not the full frame duration (1/30s), but only about 75% of it. This fraction can vary, depending on what the camera chooses based on available light or your manual settings.
     

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    Last edited: Mar 2, 2016
  16. Mar 1, 2016 #15
    I see thanks for the pictures for clearification! (Im visual person) and i think my gopro doesnt use any kind of flashes etc.
     
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