First time out with MN 190.. Canon 5D Mk III (full frame), STC Optics clip filter, no dew cap or light shield. Similar results with Pleiades image but over head and did not see central obstruction. To my east, there is an apt. complex with terrible LED based super spots which could have been reflected onto the front corrector plate (again, no central obstruction on the over head image). The "rectangles" appear after doing an Auto Background Extraction in Pixinsight. Other than using APS-C format camera (I have 7D Mk II as well).. I'm really at a loss to explain these reflections and why they appear with ABE in Pixinsight.. Appreciate any ideas.. Focus is good, visual observations excellent. Suspect something to do with clip filter (which is a rectangle) but never created an issue with other scopes (like Quattro 250).