Aperture and shutter speed in Digital cameras + general discussion

Discussion in 'Digital Photography' started by SS, Mar 30, 2006.

  1. SS

    SS Guest

    In a conventional camera an iris controls the aperture and a mechanical
    shutter is altered to control the shutter speed - is this the same in a
    digital camera? I have not 'seen' anything that looks like an iris and
    presumably shutter speed is controlled by how long the CCD is powered up or
    sampled, not a mechanical device. Of course ISO is a function of
    amplification of the signal (hence noise problems at high ISO) and focus has
    got to be by movement of the lens - or could this be done better by movement
    of the CCD? Since the lens retracts anyway i assume this function is used
    also for focus. Speaking of which how does auto focus work? i assumed that
    the camera 'sees' a small area of high contrast and then focusses until the
    change between the 'gradient' of change between the 2 areas of contrast is
    steepest (or more sudden = sharpest focus). What is the best method - do
    some cameras do a better job and why? presumably as aperture gets smaller
    focus becomes less critical as the characteristics of the lens reduce and
    the 'pinhole' effect takes over.

    Final question/tipic for discussion - as a larger CCD is supposedly much
    better re. noise why don't we see larger CCDs on (all) cameras? Surely if
    mass produced the cost increase would be negligible? Or is in camera
    software/processing going to take the lead in picture enhancement? Would
    this have to be done in camera or could the same effects be produced
    (better?) post capture?
    SS, Mar 30, 2006
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  2. SS

    Fred Guest

    On a Canon DSLR (20D) you can see the aperture opening/closing through the
    lens. Not a CCD power scenario, it is mechanical.

    I personally think that the lack of large CCD's (or the CMOS sensors with
    Canon) are due to idiotic marketing staff. I.E. The marketing/sales
    department not knowing their arse from their elbow. They could have easily
    provided full frame sensors with not that much of a cost increase to the
    consumers, but they choose not to because they can make more money by having
    APS-* sensors and also full/semi-full frame sensors.

    However, it has bitten Canon in the arse, because they have lost a huge
    amount of sales of wider 'L' lenses as a result of producing the lack of non
    full frame bodies. For example, the 24-70 2.8 is a great lens, but on a
    APS-* body, it is a crap focal range, as are the 16-35 and the 17-40 lenses.
    Also remember, crop factor makes no difference when it comes to depth of
    field. A 55mm 2.8 lens, is a 55mm 2.8 whatever.

    All DSLR's should have had a minimum of 35mm sensor size! Of course, if the
    20D had a full frame sensor, then the majority of pros would have bought one
    instead of a pro body, but the short sighted marketing staff didn't
    anticipate the huge amount of sales they would have got from 'L' lens sales
    as a result. But hell, what do I know?!? Honestly, I am tempted to go back
    to film until things settle down a bit.
    Fred, Mar 30, 2006
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  3. Where were you with this invaluable information a year or two ago? You
    could have saved all of us from the marketing geniuses/idiots of
    rich/failing Canon so we'd all have better DSLRs now for cheap. And poor
    Nikon- how come they are not "easily" producing full frame sensors?
    (Oh, Lord, please don't turn this into N v C, now, please.)

    And, have you a single credible source on costs to produce sensors?
    Figures on how much Canon has been ass-bitten over wide L lenses?
    John McWilliams, Mar 30, 2006
  4. SS

    Bill Funk Guest

    First, you lack a basic understanding of how digital cameras work. I
    suggest buying a book on digital camera use to gain that knowledge.
    This would be far better than trying to get us here to write a book in
    the group.

    The size of the sensor used will have a very large effect on other
    parts of the camera. A larger sensor requires a larger lens, which
    requires a larger body. So, compact cameras can't have a large sensor
    and remain compact.
    Bill Funk, Mar 30, 2006
  5. SS

    Bill Funk Guest

    Cost is a large factor here.
    Do you *really* think the marketing people for all the digital camera
    makers are stupid? Have you submitted your resume?
    So this hasn't bitten Nikon, or all the other DSLR makers?
    Again, you really think you know better?
    If that's true, start your own company. Or buy Sigma's DSLR operation.
    if your business plan is really as good as you seem to think it is,
    it'll be a snap to get financing, because you'll take over the DSLR
    market within 4 or 5 years!
    Good Luck!
    Bill Funk, Mar 30, 2006
  6. SS

    EO Guest

    The Point and Shoot and some others (acutally most of those that have a
    real time CCD Monitor, the new Olympus C330 being and exception) use the
    CCD and computer to set aperture (iris close down) and exposure (normal
    operation - iris fully open, 1/2 press shutter to get focus and compute
    exposure Time/WB/Aperture/etc, final press and lens closes down and
    computer and then reopens for next exposure.

    All DSLR (that I am aware of) use conventional focal plane shutters. The
    lens iris is max open, 1/2 press gets focus and determines exposure
    Time/WB/Aperture/etc (from auxiliary chip behind mirror or off to the
    side just like in film camera), full press, iris sets, mirror moves up,
    exposure by focal plane shutter, mirror drops, iris opens to max.

    Question about CCD size and direction they will go - remains to be seen
    as both equations are constantly at play - cost of 35mm size are coming
    down (very slowly), APS and smaller are getting better and cheaper.
    With RAW (as opposed to JPEG) becoming more the norm (at least in DSLR)
    more and more of the processing is being done by post processing
    software. This is especially noticeable in the profession and advanced
    amateur segment of the market.
    EO, Mar 30, 2006
  7. Cost of a sensor goes up in relation to the size of the chip.
    Sensors are made on 12-inch diameter wafers. There are a
    certain number of random defects per square centimeter.
    As the sensor size goes up, the number of chips per wafer
    goes down and the probability of a defective chip goes
    up. So, you get a high number of 1 cm square sensors from
    a 12-inch wafer, even throwing out a few defective ones.

    Draw a circle and see how many 35mm sized sensors you
    can fit in a 12-inch circle. Then pin it up on a dart
    board and throw 15 darts into the circle. How many
    chips left without holes? Now try it with 1 sq cm chips.
    If each wafer run cost $10,000, see what the cost per
    chip is.

    Roger N. Clark (change username to rnclark), Mar 31, 2006
  8. See:
    Digital Cameras: Does Pixel Size Matter?
    Factors in Choosing a Digital Camera



    Roger N. Clark (change username to rnclark), Mar 31, 2006
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