Thickness

To enter or change the thickness of a surface, move the cursor to the desired cell, and type in the new value. Thickness data is always entered and displayed in lens units, which have dimensions of length. The thickness of a surface is the distance to the next surface. The only thickness that is not used is the thickness of the image surface.

Thicknesses always change sign after a mirror. After an odd number of mirrors, all thicknesses should be negative. This sign convention is independent of the number of mirrors, or the presence of coordinate breaks. This fundamental convention cannot be circumvented through the use of coordinate rotations of 180 degrees.

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