Hi

Im a OTEN student living in New Zealand and I am currently studying 'Lens Design' and there is a section on solutions to spherical aberration, and this is how it goes:

There are 3 ways to reduce spherical aberration although it is not much of a problem in spectacle lenses.

First method: Shape factor or bending the lens. By bending the lens, we mean changing the values of F1 and F2 but keeping the power F the same. Lens designers use a quantity called the shape factor(X) which is the ratio of the radii of surfaces where:

X= r2+r1
------------
r2 - r1

Second method: stopping the pheripheral rays getting to the eye.
You can do this by using a disc on a lens with a hole or aperture cut in the middle. The eye itself has a built in stop which cuts out the rays from the edge of a spectacle lens. The iris acts as a stop and this is why spherical abberation is not considered to be a problem.

Third method: Mostly used on high plus and minus lenses. The power of the lens weakens towards the edge by using aspheric surfaces rather than spherical ones. Plastic materials are easier to manufacture than glass.

I hope this is of some help to you.
Regards
Lynette