EXIF and focus distance

Discussion in 'Digital SLR' started by John O'Flaherty, May 4, 2008.

  1. Using exiftool on a raw .cr2 file from a Canon 40D shows quite a lot
    of data about the camera, the lens, and their current settings, as
    well as data about the picture. There is information about the focus
    mode (one-shot, AIservo, etc.). One thing notably missing is the focus
    distance the lens was set to at the instant of shooting. Maybe the
    lens is not equipped to measure and report this, but it seems as if it
    might sometimes be useful information.
    Understood that temperature and current focal length setting on a
    zoom lens might make the mapping from the focus ring to actual
    distance vary, still, wouldn't it sometimes be a useful datum?
    Do any other cameras report this?
     
    John O'Flaherty, May 4, 2008
    #1
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  2. John O'Flaherty

    Paul Furman Guest

    Nikon DSLRs don't report it either. As I recall the data isn't very
    accurate, just like 3 ranges or so and it's only use is for calculating
    flash exposure.
     
    Paul Furman, May 4, 2008
    #2
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  3. John O'Flaherty

    Guest Guest

    yes they do.
    i don't know how many ranges there are, but it's much more than 3.
    however, it's not an exact distance measurement.
     
    Guest, May 4, 2008
    #3
  4. Just for another datapoint I checked some Fuji shots, and found (not
    necessarly inclusive) macro, close, distant, unknown.
     
    Blinky the Shark, May 4, 2008
    #4
  5. John O'Flaherty

    Paul Furman Guest

    Hmm, OK I see this line in my D200's exif:
    AF Focus Position - 262160
    -for a shot focused at about 75 feet away so I don't know what the
    number means.


    File: -
    C:\Users\paul\Desktop\_paul\_Pictures\2008\2008-03-25-views\orig\_PBF7291.JPG

    Make - NIKON CORPORATION
    Model - NIKON D200
    Orientation - Top left
    XResolution - 300
    YResolution - 300
    ResolutionUnit - Inch
    Software - Ver.1.00
    DateTime - 2008:03:25 19:00:10
    WhitePoint - 0.31
    PrimaryChromaticities - 0.64
    YCbCrCoefficients - 0.30
    YCbCrPositioning - Co-Sited
    ExifOffset - 352
    ExposureTime - 1/160 seconds
    FNumber - 5.00
    ExposureProgram - Aperture priority
    ISOSpeedRatings - 100
    ExifVersion - 0221
    DateTimeOriginal - 2008:03:25 19:00:10
    DateTimeDigitized - 2008:03:25 19:00:10
    ComponentsConfiguration - YCbCr
    CompressedBitsPerPixel - 4 (bits/pixel)
    ExposureBiasValue - -1.33
    MaxApertureValue - F 2.83
    MeteringMode - Multi-segment
    LightSource - Auto
    Flash - Not fired
    FocalLength - 10.50 mm
    UserComment -
    SubsecTime - 0
    SubsecTimeOriginal - 0
    SubsecTimeDigitized - 0
    FlashPixVersion - 0100
    ColorSpace - Uncalibrated (-1)
    ExifImageWidth - 3872
    ExifImageHeight - 2592
    InteroperabilityOffset - 28034
    SensingMethod - One-chip color area sensor
    FileSource - Other
    SceneType - Other
    CustomRendered - Normal process
    ExposureMode - Auto
    White Balance - Auto
    DigitalZoomRatio - 1 x
    FocalLengthIn35mmFilm - 15 mm
    SceneCaptureType - Standard
    GainControl - None
    Contrast - Soft
    Saturation - Low
    Sharpness - Soft
    SubjectDistanceRange - Unknown

    GPS information: -
    GPSVersionID - 2.2.0.0

    Maker Note (Vendor): -
    Data version - 0210 (808595760)
    ISO Setting - 100
    Color Mode - COLOR
    Image Quality - FINE
    White Balance - AUTO
    Image Sharpening - LOW
    Focus Mode - AF-S
    Flash Setting - RED-EYE
    Flash Mode -
    White Balance Adjustment - 0
    White Balance RB - 698
    Exposure Adjustment - 68608
    Thumbnail IFD offset - 2354
    Flash Compensation - 67072
    ISO 2 - 100
    Tone Compensation - LOW
    Lens type - AF-D G
    Lens - 782
    Flash Used - Not fired
    AF Focus Position - 262160
    Bracketing - 65536
    Color Mode - MODE2
    Light Type - NATURAL
    Hue Adjustment - 0
    Noise Reduction - OFF
    Total pictures - 87620
    Optimization - CUSTOM

    Thumbnail: -
    Compression - 6 (JPG)
    XResolution - 300
    YResolution - 300
    ResolutionUnit - Inch
    JpegIFOffset - 28192
    JpegIFByteCount - 9548
    YCbCrPositioning - Co-Sited


    --
    Paul Furman
    www.edgehill.net
    www.baynatives.com

    all google groups messages filtered due to spam
     
    Paul Furman, May 4, 2008
    #5
  6. John O'Flaherty

    Guest Guest

    what did you use to dump the tags?

    using exiftool on few random images of mine, i get:
    Focus Distance : 0.71 m
    Focus Distance : 3.76 m
    Focus Distance : 7.94 m
     
    Guest, May 4, 2008
    #6
  7. John O'Flaherty

    OldBoy Guest


    Latest version is 7.25
    http://www.sno.phy.queensu.ca/~phil/exiftool/

    Have a 40D myself and get FocusDistanceUpper and FocusDistanceLower.
    (I'm using EF-S 10-22, EF 24-105 f/4 L IS and EF 70-200 f/4 L IS)
    There are 2 entries of both, 1 pair of them are zero.

    Note that most (or all?) third party lenses do not report focusdistances.
     
    OldBoy, May 4, 2008
    #7
  8. John O'Flaherty

    Paul Furman Guest

    That was Irfanview. ExifTool gives this:
    FocusPosition 0x04
    FocusDistance 1.33 m

    The actual distance was about 25m not 1m. That image was with a 10.5mm
    fisheye.

    --
    Paul Furman
    www.edgehill.net
    www.baynatives.com

    all google groups messages filtered due to spam
     
    Paul Furman, May 5, 2008
    #8
  9. John O'Flaherty

    Guest Guest

    what about with other lenses?
     
    Guest, May 5, 2008
    #9
  10. John O'Flaherty

    Paul Furman Guest

    For the 70-200 VR, ExifTool says:
    FocusDistance 23.71 m
    -for a couple shots I checked at about 200 feet and at infinity, that
    same number.
     
    Paul Furman, May 5, 2008
    #10
  11. David J Taylor, May 5, 2008
    #11
  12. John O'Flaherty

    OldBoy Guest

    "David J Taylor"

    Strange, here it reports as 7.25 (Windows version).
     
    OldBoy, May 5, 2008
    #12
  13. Just downloaded it again. Discovered that I have exiftool(-k).exe in my
    EXIFtool directory, but an older exiftool.exe in the Windows directory!
    Arrgh! Thanks for encouraging me to check further!

    Cheers,
    David
     
    David J Taylor, May 5, 2008
    #13
  14. Well, thanks for pointing out the two tags - I missed them in the
    flood of data. I tried a little experiment in manual focus, to see
    what happened to the numbers as the focus ring was changed. At a
    setting of FL=28mm on the 28-135mm lens I made shots at a number of
    settings of the focus ring, at three different aperture settings, in
    case the two numbers were trying to give depth of field. Then I looked
    at the files by calling exiftool with this string, to get a little
    less data:
    exiftool -filename -fnumber -focallength -focusdistanceupper -
    focusdistancelower -hyperfocaldistance -w txt cr2s. The cr2s is the
    name of the directory. The numbers reported were the same regardless
    of the aperture setting -
    focus ring
     
    John O'Flaherty, May 5, 2008
    #14
  15. Sorry about the first, accidental post.
    Well, thanks for pointing out the two tags - I missed them in the
    flood of data. I tried a little experiment in manual focus, to see
    what happens to the numbers as the focus ring is changed. At a setting
    of FL=28mm on the 28-135mm lens, I made shots at a number of settings
    of the focus ring, at three different aperture settings (f3.5,f8,f22),
    in case the two numbers were trying to give depth of field. Then I
    looked at the files by calling exiftool with this string, to get a
    little less data and save it in files:
    exiftool -filename -focusdistanceupper -focusdistancelower -w txt
    cr2s.
    The cr2s is the name of the directory. The numbers reported were the
    same regardless of the aperture setting -
    focus ring upper lower
    maximum 655.35 81.91
    infinity 655.35 50
    10m 11 7.1
    5m 7.1 5
    3m 3.7 2.75
    1.5m 1.6 1.21
    1m 1.21 .71
    macro middle 0.71 0.47
    minimum 0.4 0.4

    The first two numbers,655.35 and 81.91, look suspiciously like
    (2^16-1)/100 and (2^13-1)/100, so they might be a way of saying
    "maximum". The other numbers correlate with the focus ring setting in
    a coarse way, but are independent of aperture, so they aren't depth of
    field limits.
    I wish Canon would publish the information.
     
    John O'Flaherty, May 5, 2008
    #15
  16. John O'Flaherty

    OldBoy Guest


    AFAIK the different values of FocusDistanceUpper and FocusDistanceLower have
    something to do with the AF accuracy.
    Haven't figured it out yet :-(
     
    OldBoy, May 5, 2008
    #16
  17. John O'Flaherty

    just bob Guest

    It is generally accepted (to the folks at dpreview forums) that the Nikon
    DSLR's report the distance and Canon's do not.
     
    just bob, May 5, 2008
    #17
  18. John O'Flaherty

    OldBoy Guest

    That's incorrect.
    EOS 400D, 450D, 40D. 1D(s) mkIII all report FocusDistanceUpper and
    FocusDistanceLower.
    As does my old Digital Ixus 400 :)
     
    OldBoy, May 5, 2008
    #18
  19. John O'Flaherty

    OldBoy Guest

    To be precise, the newest DPP v3.3 version supports lens corrections for a
    score of camera-lens combinations:
    http://gdlp01.c-wss.com/gds/0300000936/DPP3.3_M_EN.pdf
     
    OldBoy, May 6, 2008
    #19
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