Da Pentax Forum:
"Originally posted by seachongo
Can pixel shifted artifact be decreased/eliminated with faster shutter speed, say > 1/500?
No...
Originally posted by Na Horuk
But doesn't the camera have a pretty big/fast buffer? It should be able to take four 1/500 photos quite rapidly, no?
Doesn't work that way...
Originally posted by Quicksand
Unfortunately not. It's not the shutter speed that matters -- it's the interval between each of the four successive exposures.
We are getting close...
Pixel shift requires that the entire frame be exposed for the full period of time needed for all four exposures. The exposures themselves are done using an electronic shutter in the following sequence:
mirror up -->
first curtain drops -->
exposure one --> shift -->
exposure two --> shift -->
exposure three --> shift -->
exposure four -->
second curtain drops -->
mirror down
The fastest mechanical shutter speed at which the entire frame is exposed (first curtain fully dropped before second curtain starts its travel) is the X-sync speed of 1/180s (the minimum dwell for curtain movement). As a result, the effective shutter speed for stopping action is never faster than 1/180s + 4x the set exposure time + 3x the time to do a shift.
Example 1: Set shutter speed is 1/1000s for a pixel shift image
0.006 + 4(0.001) + 3(n) = 0.01 + 3(n) where n is the time to do the shift
The effective speed is a little longer than 1/100s.
Example 2: Set shutter speed is 1/10s for a pixel shift image
0.006 + 4(0.100) + 3(n) = 0.406 + 3(n)
The effective speed is a little longer than 1/2.46s
Steve
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