Focal Plane Shift

This image dissects an embryo into 9 focal planes (it can be dissected into other numbers of focal planes as well). If we count it from top to down, the first focal plane would be located at the top most and the 9th focal plane would be located at the bottom. (Note: the image shown here is at much later time in the embryo development compared to the movie showed below.)

Difference Between Focal Planes

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Movie Recorded from Two Focal Planes with Time Series: Movie on the left displays focal plane 2 while the movie in the right is from focal plane 6. As you can see, at a specific time point, you will find each focal plane records a dimension of the embryo's development. Combining all the focal planes, we are able to observe the whole embryo (3D) developing with time (4D).

Shifting Focal Planes

As you observe a 4D movie, you might encounter a focus shifting like the one you see from time point "00:21:50" to "00:22:05". How could this happen? At this early stage, the microscope operator somtimes wants to get a clearer view of the image. Thus, the focus was adjusted to obtain a better image.

See Making the Movies for a 4D movie you can shift yourself!