Hi Réjan!
Congrats on the new lens, and good to hear another favourite EF-S 17-55 F2.8 IS report
Some sidenotes: you might have a speckle of dust on a sensor or on a lens (see in front of the lens opposite of the word 'Japan')
Sidenote 2: AF and IS are both turned off on the lens
Sidenote 3: the shadow the internal flash casts is caused more by the lens's lenght than by its diameter
...and for the record: neither the 220ex nor the 430ex nor the 580ex external flashes cast lens-shadows when used in combination with the 17-55IS
And Finally:
IMPORTANT INFO FOR EF-S17-55F2.8 IS USM users:
the 'alternative 1.6x crop lenshood for the 17-40F4L', the
EW83DII, (original designed for the EF24mmF1.4L lens) also works on the EF-S17-55 IS (without vignetting), but the (dedicated designed for the EF-S17-55IS)
EW83J protects against flare a lot better!
...and as always, only *my* €0.02 worth...
Kindest regards!
Max@Home