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You do tend to get halos on brighter stars in IR. Focus is critical. Some refractors more than others will show bloating in the stars. Others not. I had a triplet APO that was bloating stars and showed diffraction artefacts around the lens clips. The FSQ106N I got later on showed pristine stars in IR. It might be the fluorite or the refractive indexes of the various lenses are different or the way it handles color correction. Reflectors with mirrors only and no glass in the imaging train are less susceptible to halos in my experience. I can't comment on the tarantula. Never imaged it in IR.
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