Re: Without intending offense

<phil-news-nospam@xxxxxxxx> wrote in message
news:dtcguq0d2v@xxxxxxxxxxxxxxxxxxxx
[snip]

I am definitely very nearsighted. I forget the exact amount or the
presciption of my glasses. However, without my glasses, I do not see
much separation of red and blue.

That's to be expected. Without the glasses point and extended sources become
always extended, so the spectrum colors blur together, except at the edges.
To see the difference at the edges, you have to have a source whose lines of
emission have at least some minimum separation. Magenta LEDs are a good
source to test this. They were discussed in another thread here sometime
ago. Also HPM blacklights.

With the glasses (one single glass
element so no chromatic correction at all) the separation of red and
blue is quite significant.

This separation again requires some minimum difference between spectral
lines. Empirically I have found that it is quite visible with the Na/Th
lines on MH's and with the Eu+/Tb+ lines on regular triphosphors. This is
most pronounced when the rest of the spectrum is relatively empty. For
sources whose spectrum contains additional stuff between the separation
candidates, the effect is less pronounced. It doesn't happen with typical
American type Na/Sc MH's for example, like the MetalArc, because their
spectrum is relatively rich.

Supposedly this could be fixed somewhat
with achromatic lenses, or better with apochromatic lenses, but I don't
want to be walking around with such thick lenses.

The pathology of myopia is extremely complicated. I am not 100% sure about
this, but I don't think that there can exist any kind of lens (achromatic or
not) that can restore a pathological eye's achromaticity like it were prior
to aquiring myopia. Reason being that myopia is not only a matter of
incorrect focusing, rather a whole series of symptoms, such as incorrect
sphericity of the eye, the iris diaphragm, etc. In fact, nobody knows
exactly what the exact causes of myopia are. It's certainly not ONE thing,
alone.

So until some major
technological innovation in extreme refractive indexes in glass or other
material, I'll just have to live with this. Avoiding fluorescent lights
is one of the things I must do.

You can avoid triphosphors, but regular halophosphate fluoros are going to
be gentler on this. Try the older warmer halophosphate fluorescents with a
temperature of 3,000-3,500 K. These contain lots of continuous emissions and
the blue mercury line (which stands at a great distance from the green and
yellow lines) is highly suppressed. I don't notice any intense spectra
around them, although again, if I look at the lamp through the edges of my
glasses I do see the spectrum.

Do keep in mind that with a continuous emission spectra, the impact is
not nearly as great as it is with 3 discrete spectral lines. A light
source that can emit, or at least mimic, a continuous spectrum, should
be reasonably workable. Incandescent works fine. I have no idea how
many discrete lines from individual, but different wavelenth, LEDs could
have the same effect.

In retrospect it has nothing to do with arbitrary differences between
spectral lines. It has to do with your glasses' pseudo-resolving power when
they act as a spectroscope. So it basically depends on your prescription. A
person with -20 diopters in each eye and glasses is bound to see spectra all
around him no matter what, simply because the pseudo-resolving power of the
lens edges acting as prisms is going to be so much greater than my
average -4.50 diopter prescription.

Again, for my -4.5 diopters, the crucial limit comes around to something
like Na(D)-Th(green) = 589 - 535 = 54nm = 540A, which is also very close to
the difference between the Europium red and Terbium green fluorescence on
triphosphors. Thus, the connundrum.

I'm just guessing that 24 would work. I wonder
if there are enough different fluorescent materials that could be mixed
in atube that could work, too.


| Phil Howard KA9WGN | http://linuxhomepage.com/
http://ham.org/ |
--
Ioannis --- http://ioannis.virtualcomposer2000.com/

.

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