Electronic shutters?

Discussion in 'Mirrorless Digital Cameras' started by tibz, Jan 2, 2009.

  1. I understand that some digital SLRs have electronic shutters, like my D50, which allows essentially unlimited sync with flashes clear up to 1/4000 of a second. I have tried this with a cheap holga flash and it worked just fine. Why, then, does the camera limit dedicated flashes to 1/500 of a second?
    Also, I've heard that others have actual shutters. Why would you bother with a digital camera? Doesn't this merely limit the sync of flashes to lower shutter speeds and take up more power? It's another thing to break.
     
  2. Your camera also has "actual shutter", that is a sometimes called a mechanical shutter.
    "Why would you bother with a digital camera? " - the sensor must stay protected behind physical shutter at all time. With removable lenses, multiplicity of problems would be invited in that was not done. Point & shoot cameras that do not remove lenses and stay sealed all the time, can efford not to use mechanical sensor protection.
    The 1/500 sec max sync limitaion is for Nikon brand flashes that are recognized by the camera. We can only guess why Nikon implemented this artificial limitation, and some guesses are:
    1. Flash duration is at 1/1000 sec or so at full power, so they need to avoid the risk of not utilizing all of the determined flash energy, that could possibly lead to underexposed or unreliable lighting, espectially since a little delay of actuation could already reduce the power. The 1/500 is a safety net for 1/1000 sec flash duration.
    2. With faster shutter sync, there are possible side effects, especially with back-lighting or high contrast harsh environments. That has been demonstrated by some, even though I did not encounter any - by avoiding taking pictures in "crazy" situations.
    3. ... other guesses..
     
  3. Nicholas, Nikon made six DSLRs with electronic shutter that you describe. D1, D1X, D1H, D70, D50, and D40. The reason these cameras still have a mechanical shutter is that the electronic shutter designs have a few quirks that make a mechanical shutter necessary:
    1. "Read out", the transfer of data from the sensor to the camera's processor, has to happen in darkness. The sensor transfers data by "shifting" it from one pixel to another, like a "bucket brigade". If there's light on it at this time, that light will add to the moving image, resulting in a "smear".
    2. If there were no mechanical shutter, the sensor would be exposed to lots of light for an extended interval before the exposure. This would overload cells, and as the overload spreads across the sensor, you get a phenomenon called "blooming". So, the sensor is kept in the dark, and the light that does fall on it in the time the mechanical curtains open is "cleared" by added circuitry that drains charge from the sensor. This draining process is not good enough to cope with the massive overload you'd get without a physical shutter.
    Right now, no camera on the market has this system. The reason it is not more popular is that it requires extra circuitry (protected charge shifting, clearing, etc) that takes silicon area away from the "light sensing" parts of the sensor, and from other useful circuitry such as blooming protection. So, sensors without electronic shutter circuitry simply have better image quality: better dynamic range, better low light sensitivity, and less blooming.
    We can only guess why Nikon implemented this artificial limitation​
    Some of us can "only guess", while others "know"...
    Nikon's max limit of 1/500 second is because older Nikon flashes had a 1/830 sec duration at full power. Since they have to allow for the camera being in full stop settings mode, 1/500 sec is the max safe setting.
    And there are no "side effects", sorry Frank.
     
  4. So wait, does my D50 also have a mechanical shutter? I wouldn't think most point and shoot cameras have shutters. How do video cameras work then? There is always light on the sensor, right, or do they have really fast shutters?
    So, the mirror flips up and there is instantly light on the sensor. Does the electronic shutter turn on sensitivity and then turn it off before read out?
     
  5. [[I wouldn't think most point and shoot cameras have shutters. How do video cameras work then? There is always light on the sensor, right, or do they have really fast shutters?]]
    Point and shoot cameras have shutters. You can see them yourself if you look down the barrel and take a picture. The shutters are open until you press the shutter button, and then they close and open again.
     
  6. "And there are no "side effects", sorry Frank." - if there are no side effects, than I should be happy and not sorry, right?. Joseph what do you have in mind ?
    The only reason I could possibly be sorry is seeing Joseph either loosing his memory, or not following closely the subject in the past.
    When D200 came in to the market, and lack of electronic shutter was discovered, D70 flash all shutter speed flash sync feature were heralded as superior to D200 camera flash features. That was abviously "politically incorrect" and even Shun provided some examples of problems (or side effects) with D70 fast flash sync.
    To counter act that some of you presented D70 pictures taken with a flash and D70 at very high sync, taken against strong back lighting, and a lot of disturbing color and other distortion was present. Those shooting conditions I called "crazy" situations.
     
  7. Nicholas,
    In video, the shutter is just opening and closing constantly, something like taking 60 exposures of 1/60th of a second to get a minute of video. Even with digital video, you have individual frames, and with the right software you can extract the frames as individual photos. So the difference between digital video and digital still is in some sense the digital file format.
     
  8. But even cheap video cameras have shutters moving that fast? I always thought the humming was the tape head...
     
  9. Video cameras have no mechanical shutter for each image. The technology used is fully electronic.
    <p>

    CMOS sensors have something called a 'rolling shutter'. Which means one row of pixels is digitized at a time,
    and one (other) row of pixels is cleared at the same instant.
    http://en.wikipedia.org/wiki/Rolling_shutter
    <p>
    This readout of one row, while other rows still collect light, leads to artifacts when the camera or objects in
    the image move. Those artifacts are frequently called 'jello' effect in discussions about the Canon 5D Mark II
    and Nikon D90.
    <p>

    CCD sensors in video cameras have light insensitive regions to store the image information ('interline'
    or 'frame transfer' architectures). The transfer of charge from the light sensitive regions to the storage
    regions is fast. Therefore CCD cameras can have real electronic shutters.
    http://en.wikipedia.org/wiki/Charge-coupled_device#Architecture
     

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