[quot]You can make synthetic HDR images: A composited three pass render at 3 different exposure levels; low, middle, high.

Actually you dont need to do this. Most renderers render every pixel internally as an 'HDR' pixel. They have to otherwise they would quickly run into rounding errors. It's just that when they have to write the pixel to file, they will clip it down to a normal LDR range.

Some of the better renderers allow you to choose whether this clipping happens or not and they support writing HDR images directly. This is what i expect them to add.