Hi! I've recently acquired a new Astromodified Canon rebel XT and I've tried to take pictures of nebulas using it but I've noticed that there are these weird black artifacts that keep appearing in my images. Would like to know if anyone has experienced this before? Or are these dirt/dust specs on the camera, filter, and telescope glass? I've attached some of my edited and raw pictures for your reference. The black artifacts can already be seen in the raw image of the horsehead nebula and after stacking I think it got amplified. Anyway, advance thanks and I hope everyone's doing well.