How do I Make my Lens Telecentric in Image Space?
http://www.zemax.com/kb/articles/256/1/How-do-I-Make-my-Lens-Telecentric-in-Image-Space-/Page1.html
By Tawnya Martin
Published on 14 August 2008
Question: It's easy to make a lens telecentric in object space, but how to I enforce the condition that it be telecentric in image space?
How to Make a Lens Telecentric in Image Space
Question: It's easy to make a lens telecentric in object space, but how to I enforce the condition that it be telecentric in image space?
A lens which is telecentric in image space has its exit pupil at infinity, and so the chief ray has zero angle with respect to the optical axis as it passes through the exit pupil and arrives at the image plane:
There are three simple ways to enforce this condition:
1. Use a chief ray angle solve on the last surface with optical power, and specify a chief-ray angle of zero:
2. Use the EXPP operand to compute the exit pupil position, and target it to some large numer. NOTE it is numerically more stable to target the reciprocal of a large number to zero, so this form of merit function construction is advised:
The EXPP operand (operand #1) has a weight of zero, so its value is computed but does not affect the merit function value. Then the RECI operand takes the reciprocal of operand 1, targets it to zero and uses a weight of 1. This pushes the value of EXPP to become very large.
3. Use the RANG operand to target the angle of the chief ray to zero.
Note that to make a system telecentric in object space, simply specify this requirement on the System...General...Aperture tab:
If this is selected, ZEMAX will assume the entrance pupil is at infinity irrespective of the location of the stop surface. All chief rays leaving the object surface will be parallel to the local Z axis. Ray aiming and field points defined using angles may not be used when this option is selected. For best performance, set the stop surface to surface 1 when using telecentric object mode.
A lens which is telecentric in image space has its exit pupil at infinity, and so the chief ray has zero angle with respect to the optical axis as it passes through the exit pupil and arrives at the image plane:
There are three simple ways to enforce this condition:
1. Use a chief ray angle solve on the last surface with optical power, and specify a chief-ray angle of zero:
2. Use the EXPP operand to compute the exit pupil position, and target it to some large numer. NOTE it is numerically more stable to target the reciprocal of a large number to zero, so this form of merit function construction is advised:
The EXPP operand (operand #1) has a weight of zero, so its value is computed but does not affect the merit function value. Then the RECI operand takes the reciprocal of operand 1, targets it to zero and uses a weight of 1. This pushes the value of EXPP to become very large.
3. Use the RANG operand to target the angle of the chief ray to zero.
Note that to make a system telecentric in object space, simply specify this requirement on the System...General...Aperture tab:
If this is selected, ZEMAX will assume the entrance pupil is at infinity irrespective of the location of the stop surface. All chief rays leaving the object surface will be parallel to the local Z axis. Ray aiming and field points defined using angles may not be used when this option is selected. For best performance, set the stop surface to surface 1 when using telecentric object mode.