Hi @Jonasz,

For a low spot RMS, I’d use a Default Merit Function with the Wizard. This is described in this article:

https://support.zemax.com/hc/en-us/articles/1500005577962-How-to-design-a-singlet-lens-Part-3-Optimization

And for the magnification, you could use the PMAG operand, or you can also use different REAY operands to take the ratio (with the DIVI operand) of different real chief ray (for different fields) heights. I’ve set this up in an example for another person in this post:

But, there’s one tip I can give you regarding maximizing an operand. While one migth be tempted to set the target of said operand to an absurdly large value, hoping the optimization will settle with whatever is achievable considering the other criterions, It usually works better for me to use the reciprocal (with the RECI operand) and target this one to zero if that makes sense. It might be usefull to play with the weight of the operand depending on what you can allow the spot size to be. Let me know if that’s not clear.

Hope this helps.

Take care,

David

@David.Nguyen has given a great answer. I second. I would just add that PMAG can be misleading. If you have a lot of aberrations, even if you’re correcting them, PMAG can return incorrect values. It is great early on in the design and then the REAY operands as ray-tracing becomes more important.

The other thought is that large magnification and small spot size are “conjugate” variables of the design. You could also place a variable on the EPD using the APER operand in the MCE. Growing the aperture with the magnification could preserve the spot size. It will gradually increase the aberration however.  Be careful with this method, as the default merit function for spot size will try to minimize transverse ray aberrations by reducing the aperture and so another method of calculating the spot size may be needed and those are sometimes computationally costly (slows down the merit function).

Thanks for the detailed answer @Michael.Young. I fully agree with both thoughts. Would you have the bandwidth to write up something about the measurement of magnification? I’d be very interested to hear your thoughts in more detail. I’ve seen similar questions about magnification in the past and it would be great to have a place to refer to. Perhaps such a resource could also introduce telecentricity, which is another topic that comes up every now and then.

Take care,

David