Geometric MTF in Tolerance tab producing different values than in Analyze?

Question

Hello. I’m new to a lot of features of OpticStudio, including tolerancing, and I have a question that likely stems from my lack of understanding of what the program is doing. In the Tolerancing user interface → Criterion tab, when in Inverse Limit mode, there is a button labeled “Check” that becomes available. I was under the impression that this checks the nominal value of the specified criterion. In this screenshot I have it set up to evaluate the geometric MTF at a spatial frequency of 8 cycles per mm (I assume those are the units?), and after clicking the “Check” button I get a value of 0.087. There is no compensation in the system.

Shouldn’t this value then be the same as (or at least close to) what the geometric MTF in the Analyze tab would provide? In the screenshot below it’s clear that the average for all fields at 8 cycles per mm is well above 0.087.

Am I misunderstanding what the “Check” button is doing? Thanks for your time!

mojtaba.falahati · Accepted Answer

Hello Emmanuel,The Limit: Check button performs a check of the nominal system based on the current criterion. As such, OpticStudio is building a Merit Function based on the criterion you chooseand reviewing the Merit Function value for the system without any perturbations.However, there are several reasons this value may be different than what the Limit: Check gives you. You may have a different sampling rate; you may have included boundary operands in your file that was not included in the tolerance check; you may be using a different method to compute MTF. When it comes to optimization, the Merit Function you build will probably be much more fleshed-out than the one we use for tolerancing. It will likely have more data and more targets to be met.I think the easiest way to understand what OpticStudio is doing is to run a single Monte Carlo trial and save it. If you want to exactly replicate what OpticStudio is doing for the nominal, you could run this Monte Carlo file when all the tolerances are zero. In the Monte Carlo file, you will see the builtmerit function, which is your criterion.The value reported when clicking on Check is just the mean of the allGMTA operands. You can then try it for eitheroption of the COMP.Hope this helps.Best regards,Moj

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