They correct the system's
color aberration as well as flatten the focal plane.
Suspecting the effect was an illusion, I tried the MV 1 on a 6-inch Maksutov-Newtonian reflector--an instrument that shows no hint of
color aberration. The view of the Moon through this scope also seemed slightly better with the filter.
(A Megrez 102-mm f/6.8 refractor is also available for $1,149.) The manufacturer conservatively labels its two Megrez instruments as "semi-apochromatic." The conservatism is laudable--I've seen similar refractors with significantly higher levels of
color aberration marketed as "apochromats," salesmanship that stretches the definition of what constitutes a color-free apochromatic refractor.
That's for top-of the-line apochromatic models, ones made of exotic glass types and multielement objectives that eliminate every trace of
color aberration in the image.
The Border Hawk showed less
color aberration than the Pro-Optic.
Not every white bird is an albino: sense and nonsense about
color aberrations in birds.
We suspect that
color aberrations such as isabelline and albinism are maladaptive in North American Porcupines, otherwise they would likely be more commonly observed in nature (sensu Caro 2005).
I'm interested in spending time with materiality--with the glitches, the surface irregularities, and the
color aberrations. When things aren't seamless, the viewer is thrown out of the film.