Why are DSLRs faster?

Discussion in 'Digital Photography' started by Charlie, Feb 26, 2005.

  1. Charlie

    Charlie Guest

    X-No-Archive: yes

    One of the reasons I bought my D70 nwas because of the lack of "shutter
    lag" and the very rapid response after turning the beast on.

    I've been enjoying those features and many others.

    A recent comparitive review of 8 MP cameras in the New York Times
    Circuits page included one DSLR, and the article described it as having
    a faster response time than the non-interchangeable lens SLR-style

    Is there something intrinsic to the basic design of DSLR cameras that
    enable their more responsive behavior, or is just that these features
    were given priority by the designers?
    Charlie, Feb 26, 2005
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  2. Charlie

    bwoag Guest

    No: many P&S cameras have fast response now.
    bwoag, Feb 26, 2005
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  3. Well, film SLRs have always had better AF and a shutter response. This
    is because the market demanded it. When DSLRs came along, the same
    response was expected, so that's why you have it.

    In all fairness, a lot of the film point and shoots are really slow to
    focus/respond. So it's more a matter of market segment than anything
    Brian C. Baird, Feb 26, 2005
  4. Charlie

    Ron Hunter Guest

    Basically, because they cost more, the manufacturer can afford to
    install a faster processor, and more ram along with a larger sensor.
    Then there is also more room for additional specialized chips which can
    do some of the work done by the CPU in other, cheaper and smaller, cameras.
    Ron Hunter, Feb 26, 2005
  5. Charlie

    Matt Ion Guest

    You get what you pay for.
    Matt Ion, Feb 26, 2005
  6. Charlie

    jean Guest

    Even a DSLR in idiot mode will be slow because it has to take care of
    everything, a nice P+S with manual controls can be fast too. Nothing
    electronic was as fast as my old film SLR, once I set everything to what I
    wanted (f stop, speed, focus) all i had to do was push the button, no lag no
    boot up, instant picture taking.

    jean, Feb 26, 2005
  7. Charlie

    Alan Meyer Guest

    I suspect that's all true. But I wonder if the larger sensor
    also helps?

    Maybe with a larger sensor that gathers more light per pixel,
    the focusing times and exposure calculation times can be reduced.
    Maybe also the post processing time needed to reduce noise can be
    less because there's less inherent noise. Maybe sharpening can
    also be a bit faster because the distinctions between adjacent
    pixels are clearer.

    That's all just speculation though. I have no idea if any of it
    is true.

    Alan Meyer, Feb 26, 2005
  8. Charlie

    Ron Hunter Guest

    Yes, but how long did it take you to set all that stuff up. I would bet
    that my $400 P&S can do all that better, and faster, than you can do it
    manually. Once I have pushed the button half-way down (the functional
    equivalent of your presetting above), there is no perceptible delay on
    it either. This wasn't the case with my older digital, however.
    Much progress has been made in this respect, both with DSLR and P&S
    cameras sold today.
    Ron Hunter, Feb 26, 2005
  9. Charlie

    Justin Thyme Guest

    Yes, their intrinsic design makes them go faster - conventional P&S digicams
    use the main sensor as their AF sensor. The circuitry analyses the image to
    determine if it is sharp (in focus) or blurry (out of focus). It then
    readjusts the lens to get focus. Because there is no way of determining if
    the object is blurry because it is closer than the focus point or further
    away, they have to try adjusting focus in both directions until they get it
    right. There is no way of telling if the image is perfectly clear - instead
    what it has to do is keep adjusting the lens until it starts becoming blurry
    again (overshot the focus point), then pull it back to the point where it
    was at it's clearest. This system is quite slow. Because this main sensor is
    a video sensor rather than a dedicated still image sensor, when the user
    presses the shutter button, the sensor needs to be cleared and charged ready
    to take the photo. Modern cameras can do this much faster than the cameras
    of only a couple of years ago. After the photo has been taken, most compact
    digi's only have one processor to take care of all the functions of the
    camera, so while it is processing the image, converting it to JPG, and
    saving it on the card, it can't simultaneously be analysing focus and
    exposure for the next image, so you can't do anything until the camera
    finishes processing the photo you just took.
    A DSLR like a film SLR has a separate AF sensor that uses phase detection
    techniques to determine focus. This system not only tells the camera how
    accurate it is focused, but tells the camera how far and in which direction
    it is out of focus. The camera can then start moving the focus motor, and
    knows exactly which direction it needs to turn. While the lens is doing
    this, the AF sensor continues to monitor how accurate the focus is, and can
    slow down the lens motor as it is nearing focus point, so that it stops
    right on focus. Because there is no trial-and-error involved, this system is
    very fast. Because the main sensor is dedicated to taking the still image
    (it's not also trying to do live preview and focussing), the camera can have
    it already pre-charged, so that as soon as the shutter button is pressed it
    can start recording. Once you have taken the photo, most DSLR's have
    multiple processing streams, that allows them to simultaneously convert to
    JPG, save the image to the card, and be analysing the data from the AF &
    exposure sensors to be ready for the next photo.
    If digi compacts used some of the techniques that film compacts use, then
    they would be faster. For example most film compacts use infrared or
    ultrasonic autofocus systems. While not as fast and accurate as the
    phase-detection system used by SLR's, these systems are faster than using
    the imaging sensor. Film compacts usually also use light sensors on the body
    to judge exposure, whereas most digi's use the imaging sensor for that as
    well. If a digi compact was made using an IR or ultrasonic focus system,
    and with a separate light sensor on the body, and if the user wasn't using
    live preview (or EVF), then then it would be possible for the sensor to be
    precharged so that the camera is ready to take the photo as soon as you
    press the button. Doing this would of course add to the cost, and since it
    is a very price sensitive market, that is usually only compared on
    megapixels and zoom, manufacturers would be reluctant to add a feature like
    this to the camera, unless it is a premium model.
    Actually, my 5 year old Kodak DC3400 has these very features, and when used
    with the viewfinder off it is much quicker than the more modern CX7430. The
    DC3400 is only a 2MP, 2x zoom camera, and when I bought it cost more than 5
    times the price of the current 4MP, 3x Zoom CX7430.
    Justin Thyme, Feb 26, 2005
  10. Thank you, at least there is one out of seven who have knowledge in addition
    to typing skills.
    Frode P. Bergsager, Feb 26, 2005
  11. PLONK
    Hap Shaughnessy, Feb 26, 2005
  12. Nope. The sensor isn't use for focus or exposure on a DSLR. There's
    a mirror and a shutter in the way.

    In fact, that's why they're so fast.

    On a P&S that uses the CCD for everything, it has to close the
    shutter and clear the CCD before it can begin the exposure.
    David Dyer-Bennet, Feb 26, 2005
  13. What were you thinking of betting? In general, I find automatic
    exposures to be quite unsatisfactory.
    David Dyer-Bennet, Feb 26, 2005
  14. Charlie

    Justin Thyme Guest

    One of my film SLR's is quite an old fully manual body. I admit that it is
    slower to set up a shot than even the slowest of todays digicams. However
    for many circumstances I don't find this limiting. For example if I'm taking
    photos of my kids playing, or of a sporting event, the lighting doesn't
    change within the space of several minutes, so I can set my exposure once
    and then I don't have to worry about it. Most of my lenses can be focussed
    by hand just as quick as most AF systems. I can then worry about pressing
    the shutter button at the best time, without fear of having to wait for the
    AF system to kick in, or for the sensor to precharge etc. Even when I'm
    using an AF body, if I'm doing any form of time critical shooting, I will
    usually turn AF off, because fast as it is, I can't afford to miss a shot
    because I happen to be pointing at a low contrast area that causes the AF to
    hunt. Even though this camera is manual wind, everything sits so comfortable
    that I can quite comfortably shoot at around 2 frames/second - for an entire
    36 exposure film if I wish. None of the digi compacts are capable of coming
    even close to that frame-rate for that number of exposures. Even most DSLR's
    can't maintain those sorts of framerates for that length of time. Admittedly
    it is very rare that I shoot more than a few frames at a time.
    So yes, my fully manual SLR is slower to set up a shot than a compact digi,
    but not significantly so. I found the compact digi would miss the shot a lot
    more often than the SLR would.
    Justin Thyme, Feb 27, 2005
  15. Charlie

    Bill Guest

    Actually, the CCD/CMOS sensor has nothing to do with focusing or
    automatic exposure in a DSLR camera.

    The sensors for those functions are reflected by the mirror up to the
    pentaprism chamber where those sensors reside. The main light capturing
    sensor is not exposed to light until the mirror moves up and the shutter
    curtains open.

    In a small digicam, the process is somewhat different and the main
    sensor is often used for many of the functions. That's why P&S cameras
    often have movie modes while DSLR cameras don't, since the sensor can be
    exposed directly.
    Bill, Feb 27, 2005
  16. Charlie

    Ron Hunter Guest

    I find them to be quite good, IF the camera is properly designed, and
    set. I find light meters, and calculations for exposure, then setting
    them, and then focusing, only to find the opportunity for a picture is
    long since past to be quite unsatisfactory.

    If you have the time to do all that, fine, but that isn't the type of
    photography I do. Try doing that on a cruise up a fiord on a partly
    cloudy day. See how many pictures you manage to get.
    Ron Hunter, Feb 27, 2005
  17. Charlie

    Ron Hunter Guest

    If you want to shoot that many shots in rapid succession, I suggest you
    buy a good movie camera. My P&S will shoot 6 shots in only about 3
    seconds. That will do for me. BTW, if you shoot a whole roll in under
    20 seconds often, your film costs must be akin to the national debt (US)!
    Ron Hunter, Feb 27, 2005
  18. Charlie

    Ron Hunter Guest

    I believe some cameras do operate that way, but mine seems to have a
    different type of focus system as it has an autofocus sensor on the
    front of the camera, just like most moderately inexpensive film cameras.
    It also has several focus modes. I find that it focuses MUCH faster
    than my older camera.
    Ron Hunter, Feb 27, 2005
  19. snipped
    A movie camera won't have the shutter speed and lenses. I suggest you
    learn what a serious older motordrive 35mm with bulk film would do.



    "History is a vast early warning system"

    Norman Cousins
    John A. Stovall, Feb 27, 2005
  20. Charlie

    jean Guest

    My sister had a 35mm Nikon SLR (I don't know the model) and on idiot mode it
    would miss pics about 50% of the time while it was hunting for the right
    conditions, not to mention the batteries which were always run down. While
    the Nikon was fumbling, I could set my FTb many times over.

    You are right, it does take time, but once it's done, click and the shutter
    releases. Don't get me wrong, I love my digital cameras, I work around the
    idiosyncracies (sp??) but sometimes you have to RTFM to get it to do what
    you want, hey, that's part of the game ;-)

    jean, Feb 27, 2005
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