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Thread: Auto modes. What is automatic?

  1. #1

    Default Auto modes. What is automatic?

    Am hoping this is not too daft a question, but it has me puzzled.

    I read useful posts by TimStannard and MidnightBlue about HD filters.

    It has affected my expectations of what video cameras do. And I am now confused.
    I remember SLR cameras in the 1980s with 'automatic' and 'manual' modes for iris control and shutter speed. In addition, it was sometimes possible to confuse the automatic mode by changing the ASA (film speed).

    I had assumed that modern cams would offer even better automated systems.
    For example, to select whether to automate the iris or the shutter speed; and also to have adjust the final sensitivity (similar to changing the ASA of film).

    But, the need for an HD filter to force an iris more open (or to have to select a shutter speed manually) suggests that the automation in our cams is less than I expected.

    I have looked at some manuals, but can't get a clear idea of state of the market. Whilst I am sure all those features exist in the most expensive cams, are they provided in the cheap (sub 1,000 UKP) range?

  2. #2
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    To dispel any confusion, I was referring to an ND filter (Neutral Density).
    Better cameras often have one or two built in (of different densities).

    The automation you talk about would not have the same effect as using an ND filter.

    Increasing the shutter speed would reduce the amount of light hitting the sensor and could be used to compensate for an increased iris - however, you may not want to increase the shutter speed.

    Now you know it's Neutral Density (and not HD) you'll find loads about this if you Google.
    Tim

  3. #3

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    (oops! Sorry, yes - I meant ND.)
    Thanks again. I see the error in my logic.
    I assumed that a final 'gain' control would negate any need for ND filters; but in fact the camera's existing auto systems are set to get the best out of the electronics which collects the photons. Any additional light would over expose the image.
    My confusion arose from distant memories of setting a higher ASA value on an SLR; and then increasing the chemical processing time of the film to compensate. But it has been a while since I sat in a dark cupboard winding 35mm film onto a processing spool.

    Thank again. Sorry if the question was a bit dumb.

  4. Default

    The question's not at all dumb.

    As you've sussed, ND filters are selected manually to achieve certain effects. The camcorder sensor (unlike film) tends to have a fixed sensitivity and the exposure is controlled by the aperture. Once that reaches the end of its range (and on camcorders with small chips, that could mean that it can't shut down to less than f8 ) it adjusts the "shutter speed" which can result in a "Shaving Ryan's Privates" effect when movement's present.

    By bunging in an ND filter you can open the lens more to get a shallow Depth of Field or avoid the pin-sharp-shutter effect.

    In fact, even when using auto-exposure on some camcorders, it will suggest "ND Filter" when things get too bright.

  5. #5

    Default

    The best use for ND filters I have found is to help the camera not to burn out the sky when you are setting the exposure of something darker. I used it most of the time in my Holy Island video. What would have been even better of me would have been a graduated ND filter. Like the Cokin range that my wife uses on her Nikon DSLR camera. HERE is an interesting article about it's use.

    You can get colour ones as well but that would be going off topic a little. I'm sure, TimA, if you come from a stills background you will be familiar with there uses to enhance sun sets etc.

  6. #6

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    Quote Originally Posted by paulears View Post
    once you get to better cameras. You have manual control of the lens aperture, manual control of shutter speed, and a manual electronic gain setting - the equivalent of the film ISO/ASA rating.
    May I plead for some more information.

    Do cams with "auto" modes tend to offer to give priority to each of these 4 settings? I appreciate that Aperture priority is probably most common; but wondered whether there were often modes for Shutter speed or gain priority.

    (I have been extremely grateful to all posters in this thread. I have tried reading cam specs and manuals, but it is hard to getting a full understanding of the state of this technology. All that coupled with my decades old fuzzy recollections of 35mm SLRs.)

  7. #7

    Default

    Quote Originally Posted by paulears View Post
    once you get to better cameras. You have manual control of the lens aperture, manual control of shutter speed, and a manual electronic gain setting - the equivalent of the film ISO/ASA rating.
    May I plead for some more information:
    Do cams with "auto" modes tend to offer to give priority to each of these 4 settings? I appreciate that Aperture priority is probably most common; but wondered whether there were often modes for Shutter speed or gain priority.

    (I have been extremely grateful to all posters in this thread. I have tried reading cam specs and manuals, but it is hard to getting a full understanding of the state of this technology. All that coupled with my decades old fuzzy recollections of 35mm SLRs.)

  8. #8

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    I've never used a camera that offers auto shutter speed or gain mode. The only auto functions I know of are focus, iris, white balance some times, There are some new fancy things like follow focus or facial recognition but thats it as far as I know.

    The camera, as far as I know, when it's in auto mode will only open and close the iris depending on the amount of light on the object you are pointing at and focus on the thing you are pointing at or the fancy facial recognition gizmo. Everything else is manual control.

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