Interfacing with Canon EOS using PTP library.

still novice, have arduino mega adk
i have installed usb host shield v2.0 librabry
and ptp canon eos library.

i trying set aperture, iso , shutter speed  on eos 7d.

i have found code ( http://www.multixmedia.org/test/usb-followfocus/followfocus.pde ) , using example sketch yanis_ptp.ino able work out
 
    eos.setproperty(eos_dpc_aperture, aperture_values) set camera aperture table
  uint8_t aperture_values[40] = {0x08, 0x0b, 0x0c, 0x0d, 0x10, 0x13, 0x14, 0x15, 0x18, 0x1b, 0x20, 0x23, 0x24, 0x25, 0x28, 0x2b, 0x2c, 0x2d, 0x30, 0x33, 0x34, 0x35, 0x3b, 0x3c, 0x3d, 0x40, 0x43, 0x44, 0x45, 0x48, 0x4b, 0x4c, 0x4d, 0x50, 0x53, 0x54, 0x55, 0x58, 0x5b, 0x5c};
no idea these numbers came there no particular reference them elsewhere.

 but can find no particular pattern these numbers (bcd, binary patterns etc) , doesn't quite work numbers don't change aperture if loop through numbers.

this standard list of aperture values:

http://www.fineart-photography.com/stops.gif

i tried converting derived aperture in stops using formula:
unsigned int temp_aperture =(int) (10.0 * pow(sqrt(2.0),(float) i/3) + 0.4 );

  3 * stops (max 15) of camera can loop through 1/3rd stop values.
even though works formula, no closer understanding numbers mean , why work, , don't.

has else tried working library, or eos camera?

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