FOCAL_LENGTH_IN_35_MM_FILE

Value is unsigned int. This tag indicates the equivalent focal length assuming a 35mm film camera, in mm. Exif 2.2 tag, usually not present, it can be calculated by:

          CCDWidth = ( PixelXDimension * FocalplaneUnits / FocalplaneXRes );
          FocalLengthIn35mmFilm = ( FocalLength / CCDWidth * 36 + 0.5 );