How do you focus HD broadcast camcorders?

Discussion in 'Professional Video Production' started by Mxsmanic, Mar 22, 2011.

  1. Mxsmanic

    Mxsmanic Guest

    In the old days (I haven't used broadcast equipment in ages), an analog
    broadcast camcorder had a small but very high-quality CRT in the viewfinder,
    and you focused the image on the CRT to focus the camera. But with digital
    camcorders and high definition, how do you focus the camera to make sure that
    the image is as sharp as possible? Does the viewfinder display contain all
    2,000,000+ pixels so that you can get the sharpest possible focus, or what?
    You can't get exact focus unless the viewfinder has at least as good a
    resolution as the final image is supposed to have. So what is the current
    method?
     
    Mxsmanic, Mar 22, 2011
    #1
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  2. Mxsmanic

    Frank Guest

    Right, and CRT viewfinders are still available for some higher end
    camcorders ($20K to $60K range), usually black-and-white but also
    color sometimes. Such viewfinder options are usually about $5000.
    If it's a consumer-grade camcorder, autofocus. If it's a
    professional-grade camcorder, operator skill and experience,
    especially in run-and-gun situations such as much ENG work.

    Note that the EVFs (electronic view finders) that are built in to
    contemporary model camcorders consist of either an LCD (Liquid Crystal
    Display) panel or an LCOS (Liquid Crystal On Silicon) display.
    You're as welcome as I am to download manufacturer's PDF product
    brochures and spec sheets and manuals and study them (and you'll find
    many of them in my Documentation Index, URL in sig), but if you look,
    I'm not sure that you'll find a single camcorder, at almost any price
    level, that actually has a 1920 by 1080 pixel viewfinder.
    If everyone truly believed that, then I suspect that few to no
    camcorders would be sold.

    Note that shooting conditions permitting, it's not uncommon to mount
    an accessory display panel, typically up to about 7-inches in size, on
    the rig so as to get a larger image at which to look, not just for
    focusing purposes, but also for more accurate framing.

    In higher-end studio shooting situations, it's not unusual to find one
    or more larger (say, 17-inch or 25-inch) displays on the set.
    Color-accurate displays of this sort are costly, however, usually well
    over $10K each. A much lower-cost alternative is the HP LP2480ZX
    "DreamColor" display, often used in post production suites.

    It's my understanding that it's either impossible or very costly to
    put a 1920 by 1080 matrix of pixels on an LCD or LCOS panel that's the
    physical size of a typical EVF, at least at the present time. This may
    change in the future, of course, as manufacturing technology advances,
    but a camcorder design engineer must also consider heat-generation and
    power-consumption related issues, not just functionality.

    There's also the question of whether 2.01 million pixels, crammed into
    the under 0.5-inch size of an EVF, would really provide any real world
    benefit to the operator.
    Pray that everything is in correct focus, given that HD footage will
    sometimes be viewed, even by ordinary consumers, on screens up to 70
    inches in size, where out-of-focus conditions will tend to become
    quite obvious to even the casual viewer.

    Note that consumer-grade camcorders employ two different types of
    autofocus techniques: EIS, or electronic image stabilization, usually
    found only in the lower-priced models, and OIS, or optical image
    stabilization, usually found only in the higher-priced models.
    Professional-grade camcorders, just like film-based motion picture
    cameras, typically offer no autofocus capability, instead relying upon
    the camera operator, or an assistant, to pull focus.
     
    Frank, Mar 22, 2011
    #2
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  3. Mxsmanic

    J. Clarke Guest

    If focus was really that difficult then still photographers would be
    having huge amounts of trouble. Still cameras today have anywhere from
    maybe 8 megapixels for a super cheap consumer model to 18 or so for an
    entry-level SLR to 80+ for a large-format.
     
    J. Clarke, Mar 22, 2011
    #3
  4. Mxsmanic

    Mxsmanic Guest

    I guess that sounds practical. It would be interesting to try. As I recall, on
    analog camcorders, if your vision was good, the resolution on the CRT matched
    what the camcorder could produce, so the best focus you could get in the
    viewfinder was also the best focus the camera could produce, so no problem.

    Of course the CRT had to be in perfect adjustment.
     
    Mxsmanic, Mar 22, 2011
    #4
  5. Mxsmanic

    Mxsmanic Guest

    Are they available because they allow more precise focusing, or simply because
    some operators prefer CRTs?
    I did look at some specs for a couple of Sony HD broadcast camcorders, but
    there was no mention of the resolution of the viewfinders.
    It's not a matter of belief, it's a matter of mathematical fact. You can't
    determine if 1920 pixels are sharp if you only have 1000 pixels to look at.
    That has long been the problem with all types of electronic viewfinders:
    unless they have at least as much resolution as the original image they are
    displaying, they cannot allow for maximum precision in focusing.
    Well, hopefully it will eventually be fixed. Do standard-resolution camcorders
    have the full broadcast resolution in the viewfinders yet?
    Since it nearly fills the visual field, it should be at least as easy to
    benefit from the resolution as it would be sitting in a room with a wall-sized
    HD television set.
    Sounds like a step backwards from older camcorders.
    Image stabilization and autofocus are different. I don't know how camcorders
    handle autofocus, but good still cameras use parallax measurement to adjust
    focus, which is very accurate (provided that you point the focus spot in the
    right direction).
    I suppose a focus puller would be feasible in studio work, but in ENG, I don't
    know. I guess you can just zoom out to the widest possible angle and fudge
    things with depth of field. It works for street photography.
     
    Mxsmanic, Mar 22, 2011
    #5
  6. Mxsmanic

    Mxsmanic Guest

    They do, if they are stuck with an EVF. That's why the best still cameras have
    optical viewfinders, which allow you to see exactly what the lens sees. I
    suppose you could put an optical viewfinder on a video camera, which would
    allow for very precise focus, but it would deprive you of a lot of information
    about the video signal the camera is generating.
    Or an optical viewfinder for pro cameras. Some have prism focusing aids, too,
    which can help a lot. But optical viewfinders wouldn't work for video, as
    explained above.

    I like the idea of a button that instantly zooms in so that you can check
    focus, although I guess it would limit you to checking focus in the center of
    the frame (but you could focus, then reframe).
     
    Mxsmanic, Mar 22, 2011
    #6
  7. Mxsmanic

    mike Guest


    And that's why you pay the extra money for a good hi-res viewfinder.
    The CRTs on my (almost) 10 yr. old JVCs (DV-550) are still crisp.
    My new JVCs (HM-700) use a 4.3" flip-out LCD panel as well as an 0.45"
    LCD viewfinder.
    The camera has a feature called "focus assist" which turns the display
    from colour to black and white and all objects which are in focus take
    on a (user selectable) colored edge.
    It sounded too strange to work effectively but, to my surprise, it
    really does its job.

    Mike
     
    mike, Mar 22, 2011
    #7
  8. Mxsmanic

    ushere Guest

    like mike i use 'peaking' more than anything else. it's proved very
    efficient.
     
    ushere, Mar 22, 2011
    #8
  9. Mxsmanic

    Frank Guest

    A bit of both I expect. Some traditions die hard.
    I don't have time right now to look up any, but I would expect that
    you'll see this specified more often on pro grade camcorders than on
    consumer grade camcorders, so I'm a little bit surprised that you
    didn't see it mentioned.
    People make do each day though, although some do use external
    displays. But it should be noted that almost none, if any, of these
    (usually around 7-inch) display panels have a 1920 by 1080 size.

    Also, as far as I know, none of the expensive pro-grade CRT
    viewfinders have particularly high res. In fact, some have what I
    would describe as low res, despite the high price being asked.
    I'm surprised that you said "yet". I mean, what manufacturer is
    working on a new SD product in 2011?
    I don't mean to be argumentative, but each pixel would have to be so
    small, and so physically close to its adjacent pixels, that I'm not
    sure there would be much benefit.

    And for what it's worth, I haven't yet seen a camcorder at any price
    point that has a flip-out LCD panel that has a full 1920 by 1080
    matrix.
    Well, as long as outlets such as CNN continue to use UGC (user
    generated content), often shot by amateurs on cell phones, it's not
    really an issue. :)
    Well of course they are! Any idiot knows that! I was having a
    conversation with someone about EIS versus OIS when I wrote that, and
    was still on my first cup of coffee to boot! Mea culpa.
     
    Frank, Mar 23, 2011
    #9
  10. Mxsmanic

    Mxsmanic Guest

    How does the camera know what's in focus and what isn't?
     
    Mxsmanic, Mar 23, 2011
    #10
  11. Mxsmanic

    Mxsmanic Guest

    So am I. In fact, even the type of viewfinder is not mentioned, and from the
    photos, it looks an awful lot like the older CRT viewfinders. Are these
    high-end HD camcorders still using CRT viewfinders?
    Then I don't see how precise manual focus could be possible without some
    special gadget to assist (like a quick zoom function).
    I suppose that's true.
    It's okay if the pixels are small. In fact, if they are too small to see
    individually, that's ideal. That would allow you to focus as best as your eyes
    can manage (within the limits of the camera resolution).

    The smallest a pixel can become and still be individually distinguishable is
    about 1/6872 of the viewing distance. So if you are looking at a screen that
    is six feet away, the smallest pixel you can see would be 6/6872 = 0.3 mm in
    size. For a viewfinder, it depends on the visual distance of the image after
    manipulation by the optics in the viewfinder.

    Anyway, 1920x1080 is far below the resolving power of normal human vision.
    It's about 1/3 the resolution that the eye can see at normal viewing distance
    ("normal" meaning a distance equal to the diagonal of the image, roughly). So
    lots of pixels can help with focusing--but there need not be more than the
    image actually contains, since focus more precise than that will only provide
    details that will be lost, anyway.
    The iReporter stuff? That's an amazing scam. CNN gets all sorts of useful
    footage for free, taking advantage of the naivete of viewers. But I've
    uploaded stuff to their iReport scam, too--stuff that wouldn't be worth paying
    for, anyway.
     
    Mxsmanic, Mar 23, 2011
    #11
  12. Mxsmanic

    Mike Kujbida Guest


    The camera has no idea.
    It's showing the operator (by using a peaking circuit) what is in focus
    by the use of the green (or red or blue) outline.

    Mike
     
    Mike Kujbida, Mar 23, 2011
    #12
  13. Mxsmanic

    Mxsmanic Guest

    What sort of peak is it looking at?
     
    Mxsmanic, Mar 24, 2011
    #13
  14. Mxsmanic

    meagain Guest

    Modern camcorders use computers to check for line and edge
    definition the same way you do. Fancy viewfinders can
    highlight where it thinks the focus problems are/arenot.
     
    meagain, May 26, 2012
    #14
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