Monday 13 April 2015

metadata - How can the aperture value written in Exif be larger than the nominal limit of the lens?


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.



Answer




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.


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