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Stereo Base and Viewing Distance

By John Wattie (kiwizone)

Considerations before deciding the stereo base

  1. How is the image going to be viewed?
  2. Is it to be orthostereoscopic?
  3. Are the shapes to have no distortion in the z plane?
  4. How skillful at stereo viewing is your audience?
 

1 Viewing distance

We have seen already that how far you sit from the viewing screen makes a huge difference to how deep the stereoscopic image will be.

Squeeze

Sit close and the round table will be a transverse oval.

Stretch

Sit back and the table is an elongated oval

No distortion

When the table is round, you are sitting at exactly the correct distance for this image.

Shear distortion

You must sit directly in front of the image. If you sway to the side, the table will distort to an oval at an angle to the picture plane. Keep swaying and the table will dance for you. Hmm, that does not happen in real life, another strange effect of 3D images on a flat surface.

3Dgogs. Red/Cyan filters are required to see the image in stereo
Red/Cyan 3Dgogs needed to see this in stereo

Down House, Darwin's study. Stereo wit stretch and squeeze

Correct viewing distance is built in to the image by the stereo base

The distance between the cameras at the time of taking the picture sets the correct viewing distance for a distortion-free experience. (That is a simplification - see later for the real story)

Changing the size of the image on the screen makes no difference, the undistorted viewing distance is not changed by magnification.

 

Down House, Darwin's study. Stereo wit stretch and squeeze Down House, Darwin's study. Stereo wit stretch and squeeze

Down House, Darwin's study. Stereo wit stretch and squeeze

The undistorted viewing distance for an image is a constant for a person, which can only be changed by distorting the image itself.

Down House, Darwin's study. Stereo wit stretch and squeeze
Down House, Darwin's study. Stereo wit stretch and squeeze
The image has been stretched sideways.
Now you sit further back to see a round table.
Original image for comparison.

 

Down House, Darwin's study. Stereo wit stretch and squeeze
Down House, Darwin's study. Stereo wit stretch and squeeze
The image has been squeezed sideways.
Now you sit closer to see a round table
Original image for comparison

 

Down House, Darwin's study. Stereo wit stretch and squeeze
Down House, Darwin's study. Stereo wit stretch and squeeze
When the picture is stretched vertical,
you sit closer to see a round table.
Original image

That is the end of my experiments with Charles Darwin's table, which is flat and circular.

I want to think about stereo roundness now, so we have to move from a table to a sphere.

Stereoscopic Roundness

1 meter away 65mm baseline

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