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Thread: How does the "uncovering" of the photosites work?

  1. #1

    How does the "uncovering" of the photosites work?

    In the tutorial on sensors it states something like this:

    When you press your digital camera's shutter button and the exposure begins, each tiny light cavity or "photosite" is uncovered to collect and store photons.

    Can anyone shed some light on how the "uncovering" of the photosites works? There are no moving parts and surely light is streaming in continuously?

    /Mack

  2. #2
    Moderator Manfred M's Avatar
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    Manfred Mueller

    Re: How does the "uncovering" of the photosites work?

    All but the cheapest cameras are equipped with a mechanical shutter, just like with film cameras. So this statement is correct. The curtains of the mechanical shutter uncover and then recover the photo sites to make the exposure.

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    Black Pearl's Avatar
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    Re: How does the "uncovering" of the photosites work?

    This might help you visualise how a typical SLR works:

    How does the "uncovering" of the photosites work?

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    dje's Avatar
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    Re: How does the "uncovering" of the photosites work?

    Quote Originally Posted by mpalomaki View Post
    In the tutorial on sensors it states something like this:

    When you press your digital camera's shutter button and the exposure begins, each tiny light cavity or "photosite" is uncovered to collect and store photons.

    Can anyone shed some light on how the "uncovering" of the photosites works? There are no moving parts and surely light is streaming in continuously?

    /Mack
    Hi Mack

    It depends on the type of camera. For an SLR, there is a mechanical shutter in front of the sensor and it operates as described by Manfred and Robin. In some DSLR's, an electronic front curtain can be used and this involves a controlled electronic reset of the pixels which simulates a moving mechanical first curtain.

    For a fixed lens camera, there is also usually a mechanical shutter in the form of leaves in the lens that open and close. With these cameras, the light is streaming in continuously in standby mode (hence live view on the back screen of the camera). When the shutter button is pressed, a global electronic reset of the sensor pixels is made (ie all pixels at the same time) and then after the required exposure time, the mechanical shutter closes for a while to allow read-out of the sensor data.

    Dave

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