Insert a dummy plane tangent to the first surface (t1=0). In the MFE, use RAID with hy=0, py=1 to get the axial cone angle. Then set RAID to hy=1, and use DIFF with py=-1 and py=1 to get the oblique angle, which will likely be a different angle than at hy=0.

@Jonasz:

You can also go to Analyze → Reports → System Data.  Then scroll down and look for object/image NA values.

or, use the OBSN operand in the Merit Function Editor:

Note: The result corresponds to the value for an on-axis field point:

Regards,

Jeff

That will give him the axial NA, which by math should agree with the RAID method.  The NA across the field will vary though, unless he specifies Object NA and object telecentricity.  Not sure if dependence of NA on object height is of interest, though.

Thank you for both answers:

1. Jeff Wilde´s answer provides an on-axis estimate of the object space NA using the built in analysis tools.
2. Mike Jone´s answer enables the extraction of the object-space NA for different field values;