Bouncing an external flash with a Nikon D5100 | Lightening and Hardware | Photo Forum

Hi,
I’m struggling with the correct exposure when using an external mounted flash (Sigma) with my Nikon D5100, when the flash is angled to bounce the light off the roof.

When the flash is set on auto and directed forward in the same direction as the camera to pointing, the correct exposure is achieved. However if I tilt the flash unit upwards, at any angle up to vertical and leave it on auto, the photo is over exposed.

Any idea why this happening? The camera must compensating for the tilt of the flash, that is increasing the amount of light emitted by the flash, but it is over compensating.