in a folded design how do you measure the 330mm using the standard triplet set, as an example do you measure say 180mm from fresnel to mirror then the remaining 150mm angled to triplet, tried to measure it out in some of the plogs but still unsure.
thank's

Use the centerline of the light path. (Sounds like you got it right.)

Yep,you got it.measure it in one straight line,then wherever you decide to intercept the line with the mirror,just bend the continuing line in relation to the ange of the mirror.