Field Lines through 1 arcsecond slit - won't fit

  • 10 February 2024
  • 1 reply

Hello there, I am still a new learner to Zemax.

I have an optical system of 7 lenses focusing collected light from a telescope onto an image plane. My goal is to image 1 arcsecond portion of the sky and add a 1 arcsecond slit. Given the F#, diameter, and EFFL of the telescope, I calculated a slit width of 0.0097 mm. 

I am running into a problem inserting a slit of this width inside the system. The field lines that pass through it have to be so small,  (0.0001, 0) (-0.0001, 0) (0,0). Is this normal to block out that much light? 


Here is a screenshot of my series of lenses. Aperture slit location is sized up and highlighted in orange. 





Here is a zoom in of the slit, only allowing (0.0001, 0) (-0.0001, 0) (0,0) field lines through.


1 reply

Hi Whit2452,

If I understand you correctly, I think you are talking about the slit height rather than the slit width. You can calculate the slit height (mm) using this formula:

Once you find the required slit height (length), you can set the dimensions of the focal plane (img) to be your slit.