Hi Callum, I was using a 10″ Dobsonian, so I had to let the image drift across the field of view. That’s how I noted the “blind spot”. Otherwise the view was as expected, showing the usual Fraunhofer interference pattern. To clarify, I didn’t see the interference pattern disappear as a result of the double, but that might have been because the slit spacing was not set quite right. More puzzling was the star (ie. its pattern) disappearing completely from view at the blind spot. That was unexpected. Unfortunately I didn’t have presence of mind to check whether it disappeared on the opposite side of the fov as well.