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Photonerd Question.

Discussion in 'Channel Zero' started by imported_Tesseract, Oct 6, 2003.

  1. Help me out dawggs,

    My digi has a manual focus setting. Since its a sony, it doesnt follow the conventional photo terms and rules...when you twist the focus ring, the indication is in meters, from 0,20m to apeiron.
    I'm trying to find the focus setting on some older pictures throught the exif tags that are embeded on the flick. The closest terms i get is focal lenght and the value is on mm. However, im pretty sure that the focal lenght has to do with the aperture, and states the ammount of focus throughout all focal zones in the picture.

    aperture: 2/ High speed = focus at one point/blurry rest

    aperture 12/lower speed = focus everywhere.

    Do i stand correct?

    can someone study that shit and give me a hint on where i can find the fuckin focus value?

    EXIF tag
    ImageDescription -                
    Make - SONY
    Model - CYBERSHOT
    Orientation - 1 (top left)
    XResolution - 72
    YResolution - 72
    ResolutionUnit - 2 (inch)
    DateTime - 2003:10:06 19:32:11
    YCbCrPositioning - 2 (datum point)
    ExifOffset - 232
    ExposureTime - 10/100 seconds
    FNumber - 2.4000
    ExposureProgram - 1 (manual control)
    ISOSpeedRatings - 200
    ExifVersion - 220
    DateTimeOriginal - 2003:10:06 19:32:11
    DateTimeDigitized - 2003:10:06 19:32:11
    ComponentsConfiguration - 1 2 3 (YCbCr)
    CompressedBitsPerPixel - 2 (average)
    ExposureBiasValue - 0.0000
    MaxApertureValue - F 2.04
    MeteringMode - 3 (spot)
    LightSource - 3 (tungsten)
    Flash - 0 (no flash)
    FocalLength - 48.5000 mm
    FlashPixVersion - 100
    ColorSpace - 1 (sRGB)
    ExifImageWidth - 2560
    ExifImageHeight - 1920
    InteroperabilityOffset - 650
    FileSource - 3 (digital still camera)
    SceneType - 1 (directly photographed)
  2. --zeSto--

    --zeSto-- Veteran Member

    Joined: Jul 12, 2000 Messages: 6,979 Likes Received: 2

    sorry... zzzzzzesto can't help you out.
  3. Focal Length
    By Phil Askey

    Focal length is measured in millimetres, it is defined as the distance from the lens to a point where parallel rays are focused to a point (diverge), traditionally measured in millimetres (mm). The lens on a consumer digital camera is marked with its focal length (or range of focal lengths if it's a zoom lens). This is typically a very small number such as 6 - 15mm, in traditional 35mm photography everyone is "used to" the common focal lengths of 28mm, 50mm, 200mm etc.

    Because the sensor in a digital camera is much smaller than a 35mm negative the lenses can be made smaller (because of this they have to be of a much higher quality), to get the true focal length you need to multiply this small size by a value called the "focal length multiplier" (this is especially important for digital SLR's which take normal 35mm lenses).

    For example, the lens on the Canon PowerShot Pro 70 is marked 6 - 15mm, however the "zoom" of the lens is always quoted as 28mm - 72mm, therefore to make the focal lengths more understandable we are actually multiplying the lenses focal length by 42/3.

    35mm Equivalent
    All digital camera manufacturers publish this "35mm equivalent" focal length simply because people are used to hearing it and knowing what kind of image a 28mm lens produces compared to a 50mm lens, some common lens sizes (focal lengths):

    <20mm = Super Wide angle
    24mm - 35mm = Wide angle
    50 mm = Normal, the same picture angle as your eye (46o).
    80mm - 300mm = Telephoto
    >300mm = Super Telephoto
    Please note also that focal length has a direct effect on perspective.

    Ok, i nailed that one...focal lenght seems to be the zoom value on the lens.

    I cant believe theres no data in the EXIF tag that tells me where it was focused....
  4. The Big Lebowski

    The Big Lebowski New Jack

    Joined: Oct 9, 2004 Messages: 53 Likes Received: 0
    The focus zones have nothing to do with the aperature. It depends on the camera how many focus zones the camera has, a standard camera would have only one whereas a canon 300d has 7 and you can set the focus with any one of them or all of them. As far as I know Exif tags dont register focus zones. But depending on the picture you can perhaps sopt where the image was focused just by looking at it. Aperature is the amount of light the camera lets in, the lower the number the more light. More light gives a softer focus though so it will not be as sharp an image.
  5. Kr430n5_666

    Kr430n5_666 Banned

    Joined: Oct 6, 2004 Messages: 19,229 Likes Received: 30
  6. Hermdog

    Hermdog Elite Member

    Joined: Nov 6, 2003 Messages: 4,504 Likes Received: 9
  7. GnomeToys

    GnomeToys Elite Member

    Joined: Jun 24, 2003 Messages: 2,616 Likes Received: 4
    What you're seeing in the EXIF is the true focal length of the lens at time of picture. That is, how far you were zoomed in and out. I'm assuming that sony didn't see it necessary to record that distance of the object the camera was focused on, and thus you probably won't have this information. I don't see anything resembling it in any of the fields there.

    If you're dealing with a camera with a non-optical viewfinder, manual focus is going to be turbo useless anyway. I'd suggest not using it.

    Here is a sample EXIF from my camera, as you can see no focal distance information on it, either. Probably not a common thing to include.

    Make - SIGMA
    Model - SIGMA SD9
    Orientation - Top left
    XResolution - 180
    YResolution - 180
    ResolutionUnit - Inch
    Software - Adobe Photoshop 7.0
    DateTime - 2004:10:24 15:42:16
    YCbCrPositioning - Co-Sited
    ExifOffset - 208
    ExposureTime - 1/350 seconds
    FNumber - 8.00
    ExposureProgram - Normal program
    ISOSpeedRatings - 100
    ExifVersion - 0220
    DateTimeOriginal - 2004:10:22 15:58:56
    DateTimeDigitized - 2004:10:24 15:29:40
    ComponentsConfiguration - YCbCr
    ExposureBiasValue - 0.00
    MaxApertureValue - F 5.66
    MeteringMode - Multi-segment
    Flash - Not fired
    FocalLength - 200 mm
    FlashPixVersion - 0100
    ColorSpace - sRGB
    ExifImageWidth - 912
    ExifImageHeight - 243
    SensingMethod - One-chip color area sensor
    FileSource - DSC - Digital still camera
    CustomRendered - Custom process
    ExposureMode - Auto
    WhiteBalance - Manual
    FocalLengthIn35mmFilm - 340 mm
    SceneCaptureType - Standard