What do you make of this?

[My2Girls66]

When I use the onboard flash, hood and the range anywhere from 18-38mm on my lens(18-135mm) I get that shadow. Must be something to do with the onboard flash and hood because it doesn't happen when I use the SB-600 w/hood or with the onboard flash and no hood at the same range. Strange that it would be on the bottom of the photo? Hmm. I wonder what could be causing it?

 

[H.E. Pennypacker]

It's because the on-board flash sits too low to completely clear the lens tube and/or hood. If you take off the hood and reshoot the same photo, the shadow will probably be gone. I say probably because you could still get a shadow with some wide angle lenses when using the on-board flash. You don't see the shadow when you use the SB-600 because it sits up higher than the built-in so the flash projects out over the end of the lens and hood.