Roland speaks of spherical aberration that means the lens is ground badly, turned edge, over or under corected.what ever the case may be. You Can not tell if the lens is bad unless the focuser is square and the Cell is colimated prior to testing it on a star. Other things like the eyepiece and seeing conditions must also be taken into acount. All this stuff while it seems overwhelming is fairly simple to learn. My suggestion is to find a local old hand at it and pick his brain. There are a million simple tricks that take the lab work out of it.. But trial by error can be heart breaking!! and expensive

Thank god for the web and guys like Pons, Lew, Robert, Grisom, and all the other old hands around here...