Hello,

   I'm exploring the use of Zemax with mirror setups in NSC mode and I'm a little confused, but then I'm a student in this field.

  In order to limit the amount of rays in disk, I launch the ray trace with a filter string where I state save only those rays which impact last my detector (which it's ABSORB as well). Good for now (checked in 3D layout, only rays going to the detector)

  Then I run the Path Analysis and I found the _1 path is listed with quite a lot of energy but the sequence showed it's not what I asked for.

  Checking, and I see it's empty. Empty? Empty but listing an energy contribution?

  I've checked with both the DB viewer and the NSC 3D layout, and yes, the ray subset _1 is empty. Also if I request the Detector Viewer to plot for subset _1, it's zero Watts.

  Mind, the Path Analysis report stated there is a non-zero total flux out for that subset. There's an energy output for that subset, and many branches (segment branching).

So now what it's really confusing me it's that if I use the total ray DB, instead of the subsets generated by the Path Analysis (_1, _2, etc),  the integrated flux at the detector is taking these rays into account when integrating the energy.

If I read with my detector using the subsets _2, _3, ... I'll obtain according figures with the Path Analysis rows. Only for subset _1 Detector Viewer and Path Analysis differ.

It would seem I get excess of energy that I don't know where it's coming from. 

I wrote a ZPL macro to split and filter out all rays and sum their independent contribution. The total energy it's indeed what I got before, but then:

(Q) What do I have inside subset _1 please? Why is it empty?

 Is really the contribution of all those rays not listed in the other paths?

So I'm lost here. Any suggestion would be welcome.

Many thanks for your time.