Nikon crop factor clarification….

Discussion in 'Beginner Questions' started by adolfo.cruz, Dec 25, 2021.

  1. I’m sorry to post this as I am sure this question has been put to rest, but I just want some clarification..

    I have a Nikon z7 ii (FX) camera and when I recently put my Nikon 12-24 f/4 DX lens on it, I know I set it down to 12. But if you look at the exif data for the following image, it’s reporting it as 18.

    From everything I’ve read and seen on YouTube, the 12-24 is always a 12-24, it never changes, only the imaging square is smaller, essentially the view. If you multiply 12 by 1.5, you get that 18 it’s reporting.

    So my question is, am I not understanding what is being explained?


  2. This is what I see when I use my standard EXIF data viewer:

    12.0 mm (35 mm equivalent: 18.0 mm)

    FocalLength 12.0 mm
    FocalLengthIn35mmFormat 18 mm

    So the focal length is reported correctly as 12mm - that doesn't change with the size sensor being used in the camera. Also reported is the ineptly named "35mm equivalent focal length", i.e. the "full frame equivalent focal length" that produces the same FOV as 12mm does on the cropped DX sensor but on the larger FX sensor - and that is 18mm. Why that information is there I don't know; for me it serves no purpose whatsoever.

    Note that the camera switched to DX mode automatically and recorded an image of
    ImageSize 5408x3600, i.e. some 19.5MP. Which is why you don't see vignetting in the above image - which would result of the 12-24 image circle not filling the FX sensor fully at its 12mm setting. IIRC, then the 12-24 can be used in FX mode for settings larger than 18mm (i.e. at 18mm and beyond the lens image circle encompasses the entire FX sensor).
    NetR likes this.
  3. Mr. Shaefer, thank you for your response. I thought I was going crazy. ;)

    Any other comments welcomed.
  4. Same happens on my Fuji using a Fuji lens. Program reads the info from the lens as 23mm and then gives its crop factor equivalent as 35mm as the camera uses an APC sensor. It's common and normal.
  5. My favorite (OS X Preview) says:

    File Source: DSC
    Flash: No Flash
    FNumber: 14
    Focal Length: 12
    Focal Length In 35mm Film: 18
    Focal Plane Resolution Unit: centimeters
    Focal Plane X Resolution: 2,301.325
    Focal Plane Y Resolution: 2,301.325

    So it specifically mentions 35mm film.

    But I do wonder about the "Focal Plane X Resolution", and especially
    that the unit is in cm. Shouldn't the unit be 1/cm?
  6. It seems clear to me that if the unit is centimeters, then the reported resolution is xxxx.xx pixels-per-centimeter. And if the unit was to be switched to inches, then the resolution would be reported in pixels-per-inch.

    In this instance the 2301.325 pixels-per-cm scales up to 3682.12 by 5523.18 pixels (20.34 Mp) over the 1.6cm x 2.4cm DX format. With no need to use reciprocal units at all.

    The only wierdness is why fractions of a pixel result, when they can't possibly be physically shown.
  7. Pixel per unit is the same as pixel/unit, or pixel × 1/unit.

    Fractional pixels only result if you take the pixel per unit spec as exact instead of what it is: nominal.
  8. No. The number of pixels per unit is multiplied by the frame size in whatever units. Not divided by it.

    The pixel number per frame height in the above case is 1.6(cm) x 2031.325.
    Pixels x 1/unit would be 2031.325/1.6 - completely the wrong result.
    So giving a nominal value to 3 (incorrect) decimal places isn't wierd?
    Last edited by a moderator: Jan 15, 2022
  9. Yes, the total number of pixels per sensor is the result of multiplying the sensor dimension by the numder of pixels per unit of length.
    So what?

    And you were totally wrong in what you said about that, not needing a reciprocal value. It is a reciprocal thing.

    And who gives nominal values to 3 decimal places?
    Last edited by a moderator: Jan 15, 2022
  10. I'm pleased we've cleared all that up, just looked out the window it's a bit foggy here also.

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