Hi Alberto

In the MTFA operand, there is an argument called Grid.

• Grid = 0 uses the auto-correlation method and calculate the MTF for only one spatial frequency.



• Grid = 1 works like the MTF analysis and is based upon the FFT of the pupil data, which is for a range of spatial frequencies.

So I think that the spatial frequency will only matter in the 1st case.

Regarding the link between the contrast operand (MECT) and (MTFT), the equations are given in that article: Contrast Loss Map in OpticStudio. I am not sure you can retrieve one from the other.

Sandrine

Hey Alberto, MECT is a proxy function that goes to a minimum as the MTF goes to a maximum, which is what makes it so useful. But you can't obtain one value from the other, otherwise that's how we would m ake the MTF operands work

Your best bet is to open an MTF plot, or MTF versus field etc before you run the optimizer and use the 'Auto Update' switch. You can toggle this during optimization so it doesn't need to be called every time. It's a great way to keep an eye on the optimization while it is in progress.

Mark,

I have a related question.   In the past I have found that tolerancing with MTF as a criterion to be problematic since after element and surface perturbations the MTF may 'bounce' off the x-axis (ie fall below zero due to a phase change) before rising at a higher frequncy.  So, for example, if the perturbed lens has an MTF of 10% at some frequency it may really be -10% and subsequent optimising with compensators would need to send the MTF first to zero before rising to a real optimimum value.  Optimisation of MTF in this case doesn't work.  Would MECT be a better (and quicker) optimisation?   When MTF goes to zero or negative what happens to MECT?  Is it monotonic?  MECT (or contrast) is not offered on as a tolerancing criterion.

Ian

Hi Ian,

The contrast optimization MECT operand uses a different algorithm to optimize for MTF. It does not directly compute the MTF using autocorrelation of the complex pupil function, or MTF as the FFT of the PSF intensity. Instead, the MECT and contrast optimization method minimizes the wavefront differences between pairs of rays separated by a pupil shift corresponding to the targeted spatial frequency, which then maximizes the MTF. In Contrast optimization, multiple sets of two rays, separated by Δ in the pupil, are traced to find the phase difference between the two rays. The optimization will attempt to drive all phase differences to zero. It's more similar to reducing wavefront slope, but it is carried out at the particular spatial frequency corresponding to Δ. In this sense, the contrast optimization might work better as a tolerancing criterion than the MTF value.

You could certainly give this a try. To use this as the tolerancing criterion, you can first set up your Merit function editor using Optimization Wizard and choose Contrast as the criterion. Then in the Tolerancing control menu, you can choose Merit Function as the criterion for tolerancing. 

If you want to know more about Contrast optimization and MECT operand, there is a webinar as well as a KBA discussing this at:

1. https://my.zemax.com/en-US/Knowledge-Base/kb-article/?ka=KA-01760

2. https://my.zemax.com/en-US/Knowledge-Base/kb-article/?ka=KA-01644

Best regards,

Hui

Hui,

Good point, I can just use it as the merit function!  Why didn't I think of that?

Ian