The "SVA" designation indicates an advanced optical design made with a super-low-dispersion ED glass center element and a Lanthanum rare-earth rear element to correct for spherochromatism
. Its lens is mounted in an adjustable, temperature-compensating steel cell.
Tolerance conditions for secondary spectrum, spherochromatism
, and fifth-order spherical aberration," Applied Optics, vol.
What is spherochromatism
? These are just a few of the questions addressed in Telescopes Eyepieces Astrographs to help you determine what telescope best suits your needs.
Under the critical and telling star test, the Nighthawk showed only a touch of spherical aberration, most likely from the spherochromatism
that almost every fast refractor exhibits to some degree.