Do not tilt a Speedlite??

I do alot of interiorshots with my EOS 1D mk II and Speedlite 550EX. Most of the time I use manual settings (ISO 250 Av 5.6 Tv 1/50) with Speedlite bounced in ceiling. This works very well most of the time but when I use the same settings and tilt my camera upright (also turning flash towards ceiling) in "portraitmode" the flash blows away the image completely (to get a descent image I have to use up to f/8 and 1/500...) If I turn my camera again and reshoot the exposure is just fine with 5.6 1/50. Why is this? Does the metering get tampered in upright mode?

My speedlites (550, 580) work fine regardless of the orientation, as far as I can see. Can you post a couple of examples (one good, one bad) with EXIF info embedded to show us what you mean?

That's very odd, sorry but I have no idea what's going on. I was going to say try the internal flash but not so much on the 1 series

Odd indeed, now I know why my hair's getting thinner...

Could it be that the light coming out of the flash is more directionally focused in the vertical plane than in the horizontal. Therefore when the camera is horizontal & the flash is tilted up, the light is truley focused on the celing, however when the camera is in portrait & the flash tilted towards the celing, a lot of direct light from the flash is sent to the subject. Try ponting it directly up instead of at an angle.
On the other hand the ETTL should compensate for this.

Have a look at the ambient exposure on the right of the picture - the 2nd is properly exposed for the ambient light but not for the stairs. What happens if you use spot metering on the stairs?

Not sure that would help, I've used centerweighted average on both and the amount of light is much alike on the two shots...?

Yeah but i'm all out of ideas apart from that.

I wonder...does this happen all the time in portrait mode or just this once? Could it just be a fluke?

Do you have the off camera flash extension cord so you can rotate either the camera or flash one at a time to see if the off exposure is a function of the flash or the camera? Maybe you've tried this already.

Looks to me like the metering's just being performed for the room in the back on the second shot, and the flash is blasting away at the stairs. In vertical position without a bracket, the preflash wouldn't hit the area to the right of the stairs so much because the stairs are blocking the "view".


Then again...the preflash should technically underexpose the shot from hitting the white stairs first.

Wierd.

Don't know why the second is overexposed. Might be a loose contact on the flash shoe, causing the flash output to max out. Give FEL a try, or put the flash on M. If it's still different, I have no idea.
I do see a hard shadow on the second, indicating that direct flash is hitting the subject?

um

Try the same shot tilting the camera clockwise instead of counted-clockwise.. ?

I suspect the metering, also, and by trying it that way you may pick up a different perspective.

CWA is biased toward the "bottom" of the frame (as seen in landscape mode); If you turned the shutter-release end of the camera up for the landscape, that area would fall on the hallway and back room, so it'd try to give that more illumination.