Question

Geometric MTF map interpretation

  • 31 May 2023
  • 5 replies
  • 88 views

 Hello All,

 

I was trying to plot the MTF for 60 linepairs/mm for 100° and 50° in x and y field.

I expect the MTF to be max in the center (close to 0° in both direction) and change radially (i think it would decrease), however, when I look at the results I am surprised to see the opposite.

Am I missing something here? I tried to look at the help section but I cannot make sense of the results.

Could someone please explain how the MTF is least in the center closer to the optical axis and gets better as the FOV increases?

Looking forward to the answers

Amit


5 replies

Userlevel 1

Hi Amit,

 

Are you getting the same result when looking at the 1D MTF window?

Are you using any Vignetting or different weight for the fields?

If you can share your file it will be easier to help.

 

Best regards,

Nadav

 

 

 

Userlevel 5
Badge +3

Is your field curved and you happen to be at best focus at the FOV edge?  Did you weight the FOV edge unusually high prior to optimization?  

Hello Nadav,

 

unfortunately due to a non-disclosure I would not be able to share the file.

I looked at the 1D MTF data and it shows the same thing. Closer to the optics axis, the MTF (average of Tan and Sag) is very bad and improves as it moves towards higher FOV.

So the lens is a fisheye 120° FOV lens with high distortion. The way I have set up my FOV is  through a grid of points (because I wanted to evaluate the PSF over the entire FOV to correlate the results of Image Simulation).

However, all the points on the FOV have the same weight of 1. And no vignetting.

 

Best,

Amit

Hi Mike,

 

good question about the optimization. Although the optimization was not run after the new “grid field” was set up, running a new optimization resulted in minimal change of the results. The MTF decreased a little more near the optical axis but the overall pattern remains the same. The MTF is still less at lower field angles and gets better at higher field angles. All the field points have the same weight.

Best,

Amit

Userlevel 1

Hi Amit,

Thanks for sharing. 

I think you need only quarter of the fields points due to the symmetry of the problem.

Maybe when you deifne it like you did  each field is weight 4 times than the center.

 

 

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