Artifacts --- Reflections or ?
The images below were made with an Astro-Physics 130 EDFs refractor, CFW-8A color wheel, and ST-10 XME camera. M42 was shot with the A-P 0.75 reducer for a focal ratio of 4.5; the Cone was done at the scope's native f/6.0. In both cases, the individual frames were 5 minutes and were calibrated with darks and flats. Separate flats were made with each filter. The contrast was jacked up to show the artifacts more clearly.
Note the spikes (not the soft vertical XME microlensing effect) radiating out from the two bright stars in m42 and one star in The Cone (NGC2264) image. These spikes are present in individual original frames, so they are not the result of rotational registration problems. These are peculiar spikes: first they are gently curved, not straight, the way spider diffraction spikes would appear (no spider in this refractor!). And second they go in at least three different directions: in the left star, they are at 1& 7 o'clock and 4 & 10 o'clock. In the righthand star, there is only one spike and it goes in the 3 & 9 o'clock direction. To me, the curve suggests a reflection off a curved surface. But why should there be three different directions? Now please scroll down to the Cone image below.
M42 (with 0.75 reducer). Please ignore the poor job of layer masking the Trapezium area into the nebula.
The Cone Nebula (below, no reducer) has only one star bright enough to generate the curved spikes, but it generates three directions of spikes.
Any comments about the cause and/or cure of these spikes would be gratefully received! mailto:firstname.lastname@example.org