Hello,
I know how should be the MTF plot (FFT MTF) of a lens design. How can I set the parameters of MTF in merit function to reach the same MTF plot? I used MTFA operands.
| Operands for MTF data |
Best answer by Mark.Nicholson
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Userlevel 4
+1
Hi Zahra,
To have the MTFA operand return the same MTF value as that’s shown in the MTF analysis plot, you can set the Grid value to 1 for the MTFA operand in the merit function.
You can find this MTFA operand settings explained in the help file at The Optimize Tab (sequential ui mode) > Automatic Optimization Group > Merit Function Editor (automatic optimization group) > Optimization Operands (Alphabetically)
Hello Hui Chen,
Thank you for your reply. It was exactly what I need.
Please see the MTF plot which is my target (for field 2) in attachment.
I have some questions and would appreciate your reply:
- why you set value for MTFA operand: 0.742298 ? from where can I find this value ?
- why you set Samp : 4
- I should set only for the maximum frequency, because you set for frequency : 50?
Userlevel 4
+1
Hi Zahra,
Thank you for your reply!
- The Value is not an input for the MTFA operand. It’s an output computed by OpticStudio. By setting the MTFA operand as I did in the screenshot on the line 1 in the Merit function editor, I’m asking OpticStudio to compute the average MTF value at 50 lp/mm at Wave 1 Field 2 with a Sampling grid size of 256x256. OpticStudio then computes and returns the MTFA value at 50 lp/mm which is the “0.731876” you saw.
- Sample 1 means 32x32. How high you need to set the sampling will depend on your system. For a well corrected system Sample 2 or 3 might be sufficient. You can start with a bit low and increase it to see if the MTF value converges.
- The MTFA operand returns MTF value at a single Frequency. This is the value “50” I entered in the MTFA operand.
Userlevel 7
+3
May I offer an alternative approach?
The problem with optimizing with MTF directly is that your design needs to already be pretty well optimized. For direct MTF optimization to work, the desired frequency should occur before the first minimum of the MTF curve, otherwise you get onto the position where the MTF has to get worse before it can get better.
That’s why we introduced contrast optimization a few years back. Like the other Optimization Wizard Image Quality options, it works with the design in pretty much any state, so it can be used when the design is far from diffraction limited. It also uses many different operands, rather than just returning a single value like the MTF* operands do. This makes optimization much smoother.
I’d suggest using Contrast Optimization as your basic image quality function in the merit function, and then use MTF* operands to tweak the final design, if necessary.
-Mark
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