A photo shot with an 1:1.8 lens contains the following exif data:

ApertureValue: 1695994/1000000  
MaxApertureValue: 16/10

How is this possible? Both values are <1.8.


You are confused because ApertureValue and MaxApertureValue are APEX values, not F-stops.

An F-stop of 1.8 is equivalent to an APEX aperture value of about 1.695994. (The formula is Av=log₂A², where Av is ApertureValue and A is f-number. See the Wikipedia APEX system page for a full explanation.)

Some exif readers (like ExifTool) convert these to F-stops for the user, but others do not.

  • 1
    Woah! I can't believe I didn't realize that. That's crazy but indeed seems to be correct. See EXIF standard here.
    – mattdm
    Mar 12 '15 at 18:52
  • According to the ExifTool docs, FNumber and ExposureTime correspond to the values we're used to working with, and ApertureValue and ShutterSpeedValue are the APEX values.
    – mattdm
    Mar 12 '15 at 19:00
  • FWIW, my Pentax camera doesn't seem to set the APEX tags at all. My Nexus phone does, however. Both ExifTool and Exiv2 convert ApertueValue to f/number for display (in this case, f/2.4), but if I look at the raw values, Fnumber is set to 240/100 and ApertureValue to 252/100 — the corresponding APEX value. Hmmm. I'm not sure if these tools are making it more or less confusing by converting.
    – mattdm
    Mar 12 '15 at 19:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.