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Thread: shallow focus

  1. #1

    Default shallow focus

    I have a question about shallow focus. In order to achieve this affect (sharp subject, blurred background) using my Cannon HV20 (61mm lens), I zoom in all the way onto my subject (10x) and then get as far away as necessary in order to obtain the correct framing. Unfortunately, this usually results in me having to stand at a ridiculous distance from the subject, which is often impossible when filming inside. Additionally, the most of a person I can frame using this technique is head and shoulders.

    So I am wondering: in a Hollywood movie production, using professional cameras, are the cameramen forced to stand so far away from their subjects to achieve shallow focus?

  2. #2
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    No.

    Shallow depth of focus is a combination of three things.

    1. The size of the chip/film frame
    2. The aperture
    3. The focal length of the lens.

    They are using film or a full-frame chip which is 24mm wide. Your chip is a quarter of that width (or a sixteenth of the area)
    Their lenses can open up to F1.1, yours has a maximum of F1.9
    A "standard" focal length for a film camera is between 35mm and 50mm, that would be a telephoto on your camcorder.

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    At the risk of spouting opinion as fact...

    Shallow DOF is not the holy grail of film making, rahter it's just another hollywood thing that we all seem to feel we have to ape to be ' professional' and look like film.

    When colour film, technicolour, became popular in hollywood the film stock had an ISO of about 6 - yes 6. Average sensitivity film is 200 to 400.

    This meant that they had to shoot with wide open apertures under lights that were 10Kw so they didnt often have the choice to get a deeper dof by shutting the aperture.

    I think it is a habit that became a rule that became a dogma.

    Shallow dof says hollywood to me.

    Deep dof says European cinema.

    Hitchcock is a glaring exception as he liked to ues huge dof with ultra close foreground in focus as well as the actors in the middle ground. ( i read that in a book so it must be true ).

    You can make good films without all that nose in focus ears blurry fiddle.

    You can also fake it in post on many shots - I occasionaly do this.

  4. #4

    Default

    So could I help my situation by buying a telephoto lens attachment for my camera? I have heard that telephoto lenses cause distortion of the image, making the foreground and background appear to be on the same plane.

    Also, Mark, I realize that Shallow DOF is not something to be used on every shot, and that it is not the only way to achieve a good look. However, it certainly makes it easier to do so. When the background is blurred, you don't need to worry about whats in it. It may seem lazy but sometimes you just cant change an ugly background.

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    Point taken about blurred backgrounds - bokeh is the cool term.

    A tele adaptor will allow you to get a shallower look but it will laso soften the image. Cheap adaptors are rubbish.

    It's a struggle to get use and control tiny dof with a consumer c corder. Most have tiny chips, as small as .16 inches. To use dof at sane zooms you really need 0.5 inch chips or greater, or ideally a 35mm adaptor but thay are expensive and have thier own problems dpending on type.

    http://en.wikipedia.org/wiki/Bokeh

  6. #6

    Default

    Thanks mark, thats exactly the info i needed. i will try to make a 35mm adapter, since i dont have $1000 to buy one. Maybe you can help me understand this though. I looked around at some instructions for making this adapter, and all the different measurements are confusing me. I am making a 35mm adapter, but the lenses i have seen used for this range from 28 to 50mm. What are each of these sizes a measurment of? is a higher mm lens better than a lower mm lens for achieving shallow dof? Also what does it mean when a single lense has a range of measurment, for example: a 35-80mm lens
    Last edited by mbrown3391; 02-06-2009 at 01:56 AM.

  7. #7

    Default

    Ok ive done some more research, but it has only added to my confusion. As far as i can tell, you have the size of the film/ccd, the physical radius of the lens, the focal length of the lens, and the zoom of the lens...all measured in miliimeters. Can anyone point me to the specifications of a lens that would be ideal for a 35mm adaptor, to achieve very shallow depth of field? also, do i need zoom?

  8. #8
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    In essence a "35mm adapter" works in two halves.

    The first bit (the bit you want to make) consists of a lens, a mount and a ground-glass (or plastic) screen. You use the lens from a photo camera to focus the image on a translucent screen. You then use your camcorder, on the macro setting, to film this screen. The theory's simple. That is a very condensed explanation. In practice most commercial adapters have a means of vibrating the ground-screen very quickly to avoid the camcorder seeing the detail of the ground glass.

    So, what you need is a camera lens. (Some adapters use movie camera lenses, the PL mount, but these are very expensive). Lenses have different focal lengths, the longer the focal length, the more like a telephoto it is, the bigger the number. On stills cameras a 50mm focal length lens is seen as "normal". In other words it's roughly equal to the human eye. Smaller numbers (35mm, 28mm etc) give a wide angle effect, longer focal lengths (135mm 210mm) give a telephoto effect. A zoom lens has a variable focal length.

    People talk about 35mm adapters because that is the width of movie film, which is also used in still cameras. What they really mean is "an adapter to use lenses intended for 35mm film, on video camcorders".
    Last edited by Rembrandt Rob; 02-06-2009 at 07:43 AM.

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    That's a really great succinct explanation Guru. I've begun in the past to read a few articles about making DIY shallow DOF adapters, but lost interest as none of those I read gave a simple explanation of the principle of the objective (how the adapter works, not what shallow DOF is).
    "Stick a spinning clear CD between 35mm lens and camcorder lens" is all I'd read before and made no sense whatsoever.
    Thanks
    Tim

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    ^^^ one 35mm adaptor uses a spinning glass disc to project the image onto. I think it is this one that works like that - a variation on that principle I guess.

    http://www.duallcamera.com/mini35-JVC-7-05.jpg

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