I had the same idea with a SD800 and a small auto flash. The flash has manual, plus two f-stop settings. I checked the manual and determined which aperature the camera used at different zoom lengths, and set the flash accordingly. If I wanted to bounce it off the ceiling, I moved the flash up a stop. If that didn't work, I used it on full manual sometimes it would work. It was a small flash after all. Worked on 8 or 10 foot ceilings very nicely. It is a digital camera. Experiment with different settings on the flash. If it is manual only, you will have to work that out between the camera manual and the power of the flash. Remember, in auto, you cannot exceed the working distance of the flash or it will fail to illuminate your subject.