So, if I understood correctly, achromatic lens group with positive focal lenght is composed of a short-focal-length convex lens with higher Abbe value and a 'weaker' concave one with lower Abbe value ('wider' dispersion), right?

BTW, apart from using material with higher Abbe values (and you say that requrement for high Abbe value and high refraction index are usually contradictory), does any manufactuter of prescription glasses use multi-lens approach to chromatic abberation elimination, as photography lens manufacturers do?

What is Spectralite?

(Is there any technical discipline we don't have a professional in here? )