Re: My first posting

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 15 Jul 97 at 18:50, Bazpan@xxxxxxx wrote:

> I believe you require some basic info about me for my first posting:-

You were *invited* to send a bio, not required....;-))

> A slightly oblique query for my debut ('off-topic', I believe it's called).

Not off-topic at all!
 
> The quality of your hearing is assessed not only by the volume (and clarity)
> of sound that you are able to perceive, but also by the frequency range. E.g.
> I can hear high-pitched whistles emitted by electronic equipment (such as
> photocopiers, T.V.s) that are inaudible to numerous friends and colleagues. I
> gather it's accepted that some people can hear beyond the normal 20khz
> ceiling for humans.
> 
> Is it possible that something similar can occur with vision whereby the
> wavelengths perceived by a person with exceptional eyesight extend beyond
> visible red into Near Infrared radiation?

Short: Yep.

Long:
Isaac Newton, in 1666 discovering the dispersion of light in all its
colors, described it as a phantom....translating to 'spectrum' in
Latin. More than a century later, Goethe, a strong follower of Newton,
nicknamed it into the Teutonic 'Farbgespenst'.... 
I stumbled upon these rather interesting viewpoints while browsing 
through Guenter Spitzing's first major piece of photographic 
literature, "Grenzbereiche der Fotografie/Infrarot, Ultraviolett und 
Polarisation" ['Limits of Photography/...'].
(thanks Helmut!)

Our eyes have their maximum efficiency at 555nm (yellow/green). To 
get the same luminance impression to the brain at 475nm (violet) or 
650nm (red), we need a factor 100x more light intensity....almost 7 
stops....

According to Professor Dr. Dr. Herbert Schober (gotta love Teutonic
nomenclatura....;-)), some people can see up to 1000nm, but it
requires 1000x (10 stops) as much light as with 555nm. Though I
personally believe this is a bit conservative, considering the 100x
(7 stops) already needed to see 650nm with the same intensity as
555nm.

800nm as boundary between visible red and invisible infrared is valid 
for an average person. Schober immediately uses J. Fraunhofer to 
illustrate the upper samples: Fraunhofer classified the 760.8nm black 
line in the solar spectrum as rather pronounced; he therefore must 
have been able to see the surrounding spectrum quite clearly.
As long as the thermal radiation doesn't influence the signal/noise 
ratio of the human eye too bad, 1000nm can be seen by several 
individuals.
A morbid joke from the laser lab crowd: you can see 1300nm quite 
clearly, but only once with that eye....8-))
(actually it is even more morbid: many moons ago, a first-hand
report in sci.optics claimed that you *heard* 1300nm more than you
saw it....<PLOP>....theoretically morbid^2 was the story of a friend, 
jobbing in a factory with a steel-cutting laser....for trouble 
shooting they sometimes operated this thing without 
protection-shielding....one had to duck while walking along....8-))

Enough sick stories, other interesting detail: Like with sound, our
vision deteriorates with age. And like with sound, the higher 
frequencies are getting problematic to see; old people have 
difficulty distinguishing violet.

Individual differences also appear in the yellow/green band, often
resulting in disputes of whether a color is green with a blue cast,
or blue with a green cast. 

On the low end of the spectrum, some people can see down to 313nm
quite clearly....the limit is not the eye sensors, but the fact that
the human eye aborbs UV quite significantly, and starts fluorescing
below that area. As I believe 380nm is the average boundary between
visible violet and invisible ultraviolet, it seems as if not every
eye absorbs as much UV.
People suffering from eye cataracts, who have their lens removed, can
see UV even better, now as a lavendel blue-grey color. I vaguely
recall that this special kind of vision has been used in
warfare....not sure.

As for seeing the kind of infrared that creates the nice effects
with HIE: the Wood effect with foliage starts at 695nm, well below
the visible limit. By coincidence, I discovered that a filter between 
89B and 88A can create a striking Wood effect even for the naked eye. 
It is very dark, shielding your eye is absolutely necessary, 89B does 
hardly show a hint of white foliage, and 88A is so dark that only 
contours can be seen. I have been pondering about fitting this color 
in one of these previsualizing eye-cups (these previsualizing filters 
already exist for both b&w and color)....I would like to assess 
interest in such a contraption, so if you are interested please mail 
me privately.

As for looking through 87: with a shielded eye, I can see light/dark 
differences very vaguely (not even real contours as with 88A).
In line with Schober: if I use the darkest filter in the 87 series, a 
87A, on one of the most bright flashlights available (SureFire NiCd), 
I can still see a very faint red. But to illustrate the intensity required 
for this 'sensation': I can *feel* heat in my eye, and a gelatine 
starts buckling within seconds....even a glass 87C filter is too hot to 
touch after 10 minutes. Note that this internal heat is caused by 
visible energy being absorbed by the filter, not so much the thermal 
energy....more than 50% is burned.

Mmm....got quite long this reply....I guess I just created another
chapter for my homepage....8-))


- -- 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
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