I recently shot a wedding and brought along my D90 and a 1.8 lens, and the results were pretty good, but not as good as hoped. I'm trying to see how much faster (if at all) the 5D is with comparable glass.

Anyone know what the baseline ISO is for each camera? In video terms I'm looking for each camera's native ASA rating (200? 320?). I'm having a hard time coming across these numbers anywhere.

Not sure what you are thinking here Ethan. Both these cameras can set the ISO, starting from 200 and going up to 1600 or so. The Canon MIGHT be a bit cleaner at higher ISO's with the full frame getting some advantage here.

In "video terms" we don't use ISO. Some have tried to describe or compare using this, but it doesn't strictly correlate. "Lux" ratings used to be popular, especially amongst amateur gear, but this was measured different ways, and became meaningless. With video cameras, even when not using db gain, the default setup can be brighter or grainier but it takes objective comparision to grasp it's low light capability.

With the DSLRs the ISO issue is that when you try to "lock" the exposure, the ISO will try to ramp to adjust. Now that's an issue begging for an update...

Not sure what you are thinking here Ethan. Both these cameras can set the ISO, starting from 200 and going up to 1600 or so. The Canon MIGHT be a bit cleaner at higher ISO's with the full frame getting some advantage here.

With the DSLRs the ISO issue is that when you try to "lock" the exposure, the ISO will try to ramp to adjust. Now that's an issue begging for an update...

What I'm trying to get at is, if you put a 50mm 1.4 lens on both the cameras under identical lighting conditions and continue to drop the lighting till the cameras begin to exhibit noise due to higher ISO (gain), how much lower could you go with the 5D as compared to the d90? (assuming you could actually lock ISO)

Has anyone run a test on this or figured out a way to measure the difference between the two cameras? I'd imagine it would be difficult to get an accurate measure as we don't know what ISO the cameras are shooting at any given moment, but it would be nice to see some sort of test even if it's just a few people eyeballing a monitor and judging when the image gets noisy on each camera.