Chromatic Aberration
Spherical aberration is the largest cause of distortion on this lens but it is not the only cause.
Color fringing (noticeable as blue and/or red fringes at high contrast transitions between black and white)
from chromatic aberration is also present, and is caused by the fact that for a lens like this the focal length for short
wavelengths (blue) is different than for long wavelengths (red).
Chromatic aberration can be significantly reduced by using achromatic lenses, which are made by combining a convex lens made of crown glass with a concave lens made of flint glass. Fortunately, inexpensive achromats are readily available. Binocular objectives are one source. Another is (you guessed it) Surplus Shed, where they sell a wide range of achromats including one with a focal length of 75 mm and a diameter of 53.5 mm.
Once again, spherical aberration resulted in soft, "glowing" images.