On 15 Jul 2003 19:18:38 -0700, (optidud) wrote:

When viewing thru a flourite such as the FS-102 which
corrects for the color Green, Blue and Red, how come
the Violet blur can't be seen as if invisible?

An apochromatic objective is corrected for three points. In a sense, that means
that nearly every color is uncorrected (except at those specific three
wavelengths.) Of course, this is not a real concern because the degree that the
other wavelengths are uncorrected is so small as to be indiscernible, or nearly
so. In particular, the eye is not terribly sensitive to short wavelengths,
especially in people over 40 or so. Also, the spatial resolution of the eye in
violet is very low. So while a few people may be able to detect some violet
fringing in an objective corrected in the blue, probably most cannot.


Only triplets
such as the AP, TMB, etc. corrects for Violet too but
not in the FS-102 or FC series yet the Violet fringe
that is supposed to be there can't be seen. However,
when we look at a person with a violet shirt, we can
see it, so what's the difference in the uncorrected
violet blur color of the doublets and the shirt.

What you call "violet" on a shirt is probably a radically different spectrum
than the spectrally pure violet you see dispersed by an optical system. The eye
is a very limited color sensor- there are thousands of different "colors" in the
sense that they contain different spectral content, but which look the same to
our eyes.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com