Now that we have a source and a reflector, we will add a refractive plano-convex lens 10mm to the right (+Z) of the detector.  Insert a line after Detector Rect in the editor and make the type Standard Lens with the following parameter values.

Ref Object:  3
Z Position: 10
Material: N-BK7
Radius 1: 300
Clear 1: 150
Edge 1: 150
Thickness: 70
Clear 2: 150
Edge 2: 150

Update the 3D Layout

Notice how we referenced the position of the lens to object 3 (Detector Rect) by entering the value 3 in the Ref Object column and specified the Z position value of 10, instead of referencing to global vertex (Ref Object = 0) and specifying 810mm for the Z position parameter. With the lens positioned referenced to the detector, the lens will always be 10mm to right (+Z) of the detector regardless of the detector position. This is how relative object positions are specified in non-sequential mode.

To see how the focused beam looks like, place another detector 650mm to the right (+Z) of the lens with the following parameters.

Ref Object:  4
Z position:  650
Material: Blank
X Half Width:  100
Y Half Width:  100
# X Pixels:  150
# Y Pixels:  150
Color:   1
All other parameters: Default

Update the 3D Layout