u/Original-Task9398

Hi everyone,

I’m trying to understand a strange artifact on my setup and wondered if some of you already experienced this.

Setup:

• SkyWatcher 150/750 (with Backyard Universe spider and full black flocking inside)
• SkyWatcher coma corrector
• ZWO ASI533MC Pro
• No filter

On bright stars, I get a weird rainbow/green halo or ghost reflection.
What’s strange is that the artifact depends on the star position on the sensor: when the star moves across the field, the halo changes position too.

It even appears on very short exposures (~3s), so it does not seem related to long exposure blooming.

I’m wondering if this could come from:

• internal reflections between the sensor window and coma corrector,
• absence of UV/IR cut,
• the coma corrector itself,
• slight dew,

Has anyone seen something similar with a Newton + ASI533MC setup?

Thanks!