Doesn't look like the keyframe button for Simple Exposure works. I did just test that the Photographic Exposure camera settings DOES indeed animate. As I was reminded recently by TomG, you need to add Photographic Exposure to the Tone Mapping stack and you must disable the Simple Exposure option. Now when you select the Corona Camera tag, you can adjust the ISO, Shutter and F-stop like a real camera. I was able to keyframe the f-stop from light (f/2.8) to dark (f/22) with ease. Hope this helps.