Originally posted by enoeske Real Resolution (pixel shift) uses an electronic shutter for the 4 exposures and doesn't use the mechanical one.
The exposure sequence begins with the mechanical shutter closed. Therefore the total time is gated by the curtain speed to open/close the opening. This is basic focal plane shutter stuff. I chose the 1/180s figure because it is the nominal X-sync speed which in turn is based on the speed of the curtains. The real sequence is a little more complicated, but distills to the
same similar logic:
- Shutter release pressed
- Mirror up
- Electronic shutter closed
- Leading mechanical shutter curtain begins travel
- Leading mechanical shutter curtain reaches end-of-travel (EOT, frame is now fully open)
- Leading mechanical shutter curtain EOT confirmed
- Pixel Shift exposure #1 *
- Shift #1 **
- Pixel Shift exposure #2
- Shift #2
- Pixel Shift exposure #3
- Shift #3
- Pixel Shift exposure #4
- Trailing mechanical shutter begins travel ***
- Trailing mechanical shutter EOT (frame is now fully obscured)
- Mirror drops and mechanical shutter resets to ready state
* All pixel shift exposures are done using the electronic shutter at the shutter speed indicated by the exposure system. E.g. If 1/1000s, the time for each will be 1 ms or 4ms total for the actual exposures.
** I am assuming that the electronic shutter will reset/restage during the shift operation along with sensor reset and data flush. The time required for the combined operation is unknown, AFAIK, but is assumed to be speedy.
*** Image processing likely begins as the trailing curtain begins its travel. The camera will not be able to process another frame until this is accomplished.
As I was typing this last little bit, it occurred to me that I have been fuzzy in my thinking and explanation. The total cycle time is per the above sequence.
The pertinent time window for subject motion of the PS system is simply the time it takes to do the four exposures + the time to shift/restage/flush. As such the mechanical shutter component is sort of a red herring unless the concern is total time per cycle.
Edit: In case it is not obvious, @enoeske is quite correct. I have bolded the time-critical steps for subject motion for emphasis.
Steve