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Hello there, 

I have an optical system of 9 lenses focusing collected light from a telescope onto an image plane. The line on the far left of the design is the focal plane from the light collected from the telescope. This imager will double as a spectrograph when a prism/grating is added into the collimated beam. Because of this, I need to know where to place the STOP in this design.

Original design: 

AGV_vUd7SQ7-fzj1lwfV03LN0QVzMEnlKxS8078BQ2uotfhM6fMZSOZPX4ia9vSjlUPskGV8Jo8p3K1QHWNDLKcwlbX0HW5KQTU61xA5xwJ1AUAvWczht5ZVLlt4252Bhr2zUoKte0viCA=s2048?key=54XQhJMCOY4xx-YpKaaYhQ

 

 

I understand the STOP position will be located where the image of the secondary mirror is formed.

 

Attempt 1 to find STOP position: 

In my attempt, I set the OBJECT to be the secondary mirror which is 3913mm before the focal plane. (Should this have infinite thickness?) The height of the secondary mirror source is set to be 118mm by adjusting the field lines. I then set the STOP surface to be where the focal plane is. (Should I set the secondary mirror to be the STOP position since that is where the light is originally focused?) Finally the aperture is set to a value so the rays reaches top and bottom of the field lens, lens following the focal plane. 

 

 

I know I am doing something wrong in this approach, what do you think I should change? Am I on the right track? I’ve tried different methods before submitting this help request, but none seem to work well either. Thank you greatly for any guidance!!

 

 

 

You're wanting to relay the exit pupil of the Cassegrain (usually behind the secondary) to a new position, right? I usually put the Zemax stop on the primary mirror rim, then synthesize the second stop directly on the center of the grating aperture.  Use REAY and REAX operands to create the second pupil by defining the aperture needed.  For example, say the new pupil is 32mm diameter at some wavelength on grating surface 28. Define the top of the pupil first, by setting py = 1 and incrementing hy:

REAY 28 wvln  0   0.3   0   1   16

REAY 28 wvln  0   0.4   0   1   16

etc.

REAY 28 wvln  0   1.0   0   1   16

To define the low side of the pupil, repeat the sequence with py = -1.0 and target = -16mm.  Then define the +X side using REAX, px = 16 and hx from 0.3 to 1.0.

This will form the second pupil as cleanly as pupil aberrations will allow.  Use Footprint to see how clean the pupil image is.  Works great for me, but other methods are certainly possible.

Mike


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