Re: Sagittal plane for an off-axis object point


<sibaken@xxxxxxxxxxxxxx> wrote in message
news:1190292403.209536.321770@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hello everyone,

For an off-axis object, To my knowledge, tangential plane contains the
chief ray and the optical axis.
Actully tangential plane is y-z plane.
But can someone point out sagittal plane for me?
Sagittal plane is the plane that contains chief ray and x-axis or the
x-z plane?
Suppose z-axis is optical axis, ordinate is x-axis and abscissa is y
axis.

Thanks in advance.


Here is a quotation from the ZEMAX manual, perhaps this will help:

---------------------------------------------------------------------------------

The term "tangential" refers to data computed in the tangential plane, which
is the plane defined by a line and
one point: the line is the axis of symmetry, and the point is the field
point in object space. The sagittal plane is the
plane orthogonal to the tangential plane, which also intersects the axis of
symmetry at the entrance pupil position.
For typical rotationally symmetric systems with field points lying along the
Y axis, the tangential plane is the
YZ plane and the sagittal plane is the plane orthogonal to the YZ plane
which intersects the center of the entrance
pupil.
The problem with this definition is that it is not readily extended to
non-rotationally symmetric systems. For this
reason, ZEMAX instead defines the tangential plane to be the YZ plane
regardless of where the field point is, and
tangential data is always computed along the local y axis in object space.
The sagittal plane is the orthogonal to
the YZ plane, and intersects the center of the entrance pupil in the usual
way, and sagittal data is always computed
along the x axis in object space.
The philosophy behind this convention is as follows. If the system is
rotationally symmetric, then field points
along the Y axis alone define the system imaging properties, and these
points should be used. In this case, the
two different definitions of the reference planes are redundant and
identical. If the system is not rotationally
symmetric, then there is no axis of symmetry, and the choice of reference
plane is arbitrary.


.

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