I prefer to do this kind of thing using the Exposure control of Magic Bullet Colorista, but that plug-in is not yet ready for CS4.
For similar issues, I often use the Levels and Highlight & Shadow to do the final density grading. Where there are changes in a Clip, I Razor the Clip, as is necessary, and apply the appropriate Effects. To "soften" the changes, I will add Cross-Dissolves to my newly "Razored" Cips. As the Handles are built in from the original longer Clip, the "transition" is almost always smooth and unnoticable.
Because you mentioned "key framing"...I am wondering if you have ridden the iris during the take (clip) using the zebras as a guide?
If so.... you have created a whole mess of whoop ***!
Zebras are more so a Level control than an exposure control. ( I know some will argue this).
EDIT: I amused that one can not say arse in this forum.
Hi, Yeah you're correct. I have attempted to increase exposure during filming. I thought I could edit it easily but it seems this may take me longer than I thought.
I assume it's best to leave exposure changes and edit in post while filming seeing that I have increased my workload somewhat.
I think I'll give Hunts tip a go. Cheers.