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There is another source of these "diffraction spikes".
You say that there is a lot of light pollution where you are. Venus is quite low in the sky for us here in Oz and in the west. I actually suspect that what you saw was internal reflections of stray bright lights entering the OTA, say from local floodlights or streetlights. If you were pointing the scope low in altitude, it is very likely this was the source of your spikes.
If your scope did not have a dewshield fitted, these stray light internal reflections are common. The stray light enters at an angle and reflects off all manner of surfaces inside the OTA: baffle tube, baffle tube stops, secondary mirror baffle. These are the main sources for this sort of aberration with Maks & SCTs as there are no spiders to create these spikes. Even the Moon can create these internal reflections when it is kept just out of the field of view of the eyepiece, as can Venus and Jupiter because of their brilliance.
This lack of control of internal reflections is a major source of loss of contrast with many scopes regardless of design, refractors and reflectors (chose your flavour of reflector). It can also affect high end scopes as these internal reflections can be very sneaky in the way the are produced. Even the design of the baffle tube on how it is supposed to control these reflections may be undermined because the paint that the baffle tube is finished with is just too reflective on a sharp edge.
It is possible to improve the control of these internal reflections, but it takes time to chase down the various offending surfaces and a willingness to open up the OTA and apply a suitable paint (such as Black 3.0) on these surfaces. I am considering doing this on my own 9" Mak after seeing the stupendous contrast of a friend's 10" Mak! Same eyepiece and diagonal, same object (Moon), and the difference in contrast was staggering, and it was entirely because of the design of the baffle tube of that 10" Mak and the paint used in those critical areas. And the contrast in my 9" Mak I thought was pretty good!
Alex.
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