Ray Tracing Moana

OSLO EDU is a free Windows program for optical design. It is restricted to 10 surfaces, just enough to evaluate a Newtonian with a double-doublet lens corrector. The surfaces are: entrance window, primary, secondary, 3 surfaces per doublet (2 doublets) and image.

The Oslo file is offered below. The sketch shows the optical layout, and the table provides the optical prescription for Moana.

One remark: the actual Paracorr prescription is not public. It is very unfortunate, but Televue keeps the Paracorr prescription a trade secret. So I am using instead an analog, the coma corrector described in Smith-Ceragioli-Berry p389. It is understood the actual Paracorr type 2 is at least as good, hopefully better, than the SCB corrector shown below.

Another remark: when looking at the spot diagram, the black circle is 6.2 microns. It is the actual diffraction limit of the scope, given by r = 1.22λf/D. So at a wavelength of 550nm (ie green light), Moana has a 1.09 arc-second resolution, corresponding to a 6.2 micron airy disk on the sensor (2 pixels with the current CMOS camera). This is a match made in heaven between the seeing (rarely below 1 arc-seconds), the scope diffraction limit (1.09 arc-second), the tracking precision (usually around 1 arc second RMS) and the camera pixel size (1 arc second for two pixels).

Just keep that 6 micron scale in mind when comparing the spot diagram provided for Moana with those found on commercial websites selling telescopes, as many sales people rescale their diagrams to make the spots look smaller! A company notorious for engaging in this practice is Takahashi, sporting a 100 microns scale on their spot diagrams!