Hi Cameron,

That’s a nice piece of code you’ve written there.

In general, I always prefer to get data using available operands rather than the GETwhatever keywords. Back in the day we wrote GET* keywords for every analysis feature, but soon realized that this would end up with hundreds of keywords. Instead, we wrote the OPER/OPEV keywords that allowed you to call optimization operands directly. Since every analysis feature already comes with optimization operands, this was way more efficient.

For MTF there is an additional reason to use operands. As you said, GETMTF will calculate the entire spectrum of response, and then return the desired values. There are two ways to compute MTF, by Fourier transform of the pupil function, or by autocorrelation of the pupil function. Since when optimizing we want data at a specific frequency, we use autocorrelation to produce the data at the specified frequency, rather than getting the whole spectrum and then extracting the single value needed.

You could also write a merit function (or a macro that writes a merit function) that computes all the data you want. Save it as MyMerit.MF, load it and read it out line by line to get the data you want. Assuming you want the same data returned many times, that would be my preferred approach. Also, if you use an MTFT(settings) then put the MTFS(settings) on the next line. The T operand computes both T and S, and caches the S for the next operand. That cache gets flushed if the next operand is not the corresponding S operand, so you can speed up the calculation by a further factor of two through the order in which you get the data.

• Mark