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Thread: 7D can Catch a Bullet

  1. #31
    Senior Member
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    Jan 2009
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    327

    Re: 7D can Catch a Bullet



    Something that needs to be pointed out here is that imaging a fired bullet is not intrinsically difficult--but imaging one so that it can be seen as a sharp, clearly defined object, is much more challenging, and NOT possible without the use of strobes.


    For any shutter speed faster than the sync speed, there is no point in time during the curtain travel in which the entire sensor is fully exposed to light. A 1/8000s shutter speed, for example, does not mean the shutter curtains are traveling any faster than at any other shutter speed. For all shutter speeds, the curtain travels at the same velocity across the sensor. The speed of the curtains imposes an upper bound on the sync speed.


    A fast exposure is attained by simply narrowing the gap between the first and second curtains so that only a small fraction of the sensor is exposed at any given time during the curtain travel. The consequence of this with respect to imaging a bullet is that:
    1. It is not possible to predict where the bullet might show up in the frame, or depending on the scene geometry, it may not appear at all.
    2. The bullet may be blurred due to the fact that it is still traveling too fast.
    3. The bullet's shape is likely to be distorted (example: http://en.wikipedia.org/wiki/File:Fo...istortions.jpg)



    The only way to actually completely freeze a very fast-moving object is to light it with a strobe. This is how Harold "Doc" Edgerton did his high-speed photography (e.g. the iconic milk drop and bullet through an apple photos). The shutter is left open and a single precisely timed strobe is the sole light source. The effective exposure is then determined by the strobe duration and lens aperture.

  2. #32
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    Re: 7D can Catch a Bullet



    Wickerprints.....you're correct.....to "freeze" a fast moving object you must use a short duration pulse of light as the sole light source at which point shutter speed is almost irrelevant. For a bullet you probably need a flash duration of 1/20,000 sec. orless to"freeze it"


    Commonly used camera flashes in manual mode will shorten the flash duration as you dial the power down but of course the light output gets lower as well. That is why many who photograph things like hummingbirds will use severalflash units synchronized together.


    The point of this postis merely that you can actuallyhand hold a camera and be ableto captureeven a blurred image of such a fast moving object. The timing is a guess and I had to shoot about 100 frames to get 2 that showed the projectiles in flight.


    It CAN be done but requires some lucky timing or many repeated attempts.


    Joel

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