Lower spherical is a very well known feature of telescopes. Both lower and higher lead to a significant difference in the out of focus images. One side of the focus is brighter than the other . But it is a telescope induced error that is mainly the effect of the design of a telescope. In this case the edge of the mirror is having a different curve than the other parts of the mirror.
Some people simply cover the outer edge of such mirrors to erase the effects.
They reduce the aperture that way but increase the image quality. Too often vision will be degraded due to turbulence. However the higher atmospheric layers also are turbulent. Due to minor deformations in the mirror made during production a mirror can suffer from roughness. The effects are much alike turbulence except that they are static and will not disappear.