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Thread: Query about mirror vibration

  1. #1
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    Default Query about mirror vibration

    Hi folks,

    I came across the below statement from a book & don't fully understand about the pixels saturation.

    "The mirror lock-up feature is best used at shuttle speeds of around 1/15 second or faster. The long shutter speeds don't really require mirror lock up, as the mirror vibrations are long gone before pixels begin to saturate".

    Appreciate your views on this for me to better understand this statement.

    Cheers,
    Ben
    Last edited by UncleBen; 21st January 2010 at 01:36 PM.

  2. #2
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    Default Re: Query about mirror vibration

    Quote Originally Posted by UncleBen View Post
    Hi folks,

    I came across the below statement from a book & don't fully understand about the pixels saturation.

    "The mirror lock-up feature is best used at shuttle speeds of around 1/15 second or faster. The long shutter speeds don't really require mirror lock up, as the mirror vibrations are long gone before pixels begin to saturate".

    Appreciate your views on this for me to better understand this statement.

    Cheers,
    Ben
    First it's shutter, not shuttle. A shuttle is something that moves back and forward between two locations.

    Pixel saturation is a simple term for "pixel well saturation" which is the amount of time it takes a pixel to receive enough light photons to produce a specified voltage which is then read and interpreted as part of the R-G-B value of the colour.

    You can use the analogy of a water well to represent a single pixel. Each colour requires 3 pixels one with a red green one blue filter on top of it. Each of these sub units is like a water well, it has a "depth" that is measured in electron volts. As light (photons) strike the pixel the 'well' fills with captured photon energy and thus the voltage increases. After the correct amount of time (shutter open time) the capture of photons ceases and the individual values for each pixel are read on the sensor and by combining the RGB values a single colour value is found, this is then stored in the correct sequence as the digital image.

    I hope you understand this.

    Now to the mirror.

    As the reflex mirror moves up and down through an arc it causes vibration (mirror slap) at each end of it's movement. This is because the mirror is moved violently and very quickly. Camera companies use a variety of methods to reduce this slap including some very expensive techniques such as dampers and titanium components to reduce the moving mass and also to reduce the vibration.

    Using a mirror lock up technique is quite common in some of the cheaper bodies (not to be confused with the very expensive manual mirror lockup used in professional grade DSLR's) where the mirror is quickly flipped up just before the shutter opens and held open by electromechanical means until the image is taken and then released. This results in less in camera vibration and hopefully better quality images. Doing it this way is cheaper than building in proper anti-mirror slap methods. However this type of mirror lock comes at a price and that is a reduced frame rate (frames per second) that the camera can take.

    Hope this helps.
    The Ang Moh from Hell
    Professional Photography - many are called, few are chosen!

  3. #3

    Default Re: Query about mirror vibration

    at long shutter speeds, the effect of the miror slap will be reduced because the sensor will not be sensitive enough to pick up the effect from the vibration which happesn in a split second and that normally doesn't contribute to the final exposure which can last more than 30 secs.

  4. #4
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    Default Re: Query about mirror vibration

    Crystal clear! Thanks a lot! Not forgetting to thanks Ian for correcting my grammar .

    Cheers,
    Ben

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