On my D7000 in live view mode, taking a picture performs these steps:
- (Mirror is up, aperture is stopped down.)
- Shutter closes.
- Aperture opens all the way.
- Aperture closes back down.
- Shutter opens and closes.
- Aperture opens all the way back up.
- There's a pause of about half a second between these steps.
- Aperture closes back down.
- Shutter opens, live view resumes.
Why does the aperture need to move at all? Couldn't it simply stay stopped down?
- I'm in manual focus, so it's not autofocus.
- I'm in manual exposure mode, so it's not metering.
- I've set white balance manually, so it's not white balance
- The high dynamic range mode (Active D-lighting) is off, so it's not that.
- Flash is off.
I have noticed that if I change the aperture setting during live view, the aperture doesn't change right away - when you take the picture, it opens all the way up, then closes down to the new aperture setting. This doesn't explain why it opens and closes after the picture, though, since it stays at the new aperture.