I bought myself a nice 32mm (2" fitting) eyepiece with a 'wide view'. I was disappointed to see a dark patching the middle when I looked through the scope in daylight. I have never been aware of this when looking at (brilliant) wide objects at night. With its wide angle view, it gives the impression of looking out of the spacecraft window. I bumped into a Q and A about various things and it did include this question. The given answer was because of the wide exit pupil of the lens and the narrow aperture of the eye in daylight. I wonder if anyone has a source of a diagram that would make that explanation any clearer. I can't sketch anything out that convinces me. At least reading about it implies my lens is not, as I first thought, a duffer.