Re: WJ & light leakin Hoya's

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

On  7 Sep 99 at 12:14, Cameron Shaw wrote:
 
> > Well, at least Hoya didn't claim it was opaque ;)
> 
> This is an interesting message, yes it does leak light but it is
>  designed to pass light around about 720nm and longer wavelengths.
> ( Hoya R72). However I am of the opinion that it is just on the
> border of visible/invisible light to the human eye.

The limit, at daylight intensities, is 780nm, give and take some 
variation between samples (humans....;-)).
According to sci.optics, there hasn't been done much significant 
research to the light/visual perception of the naked eye since 
1924....which makes a book from Helmholz from before that era one of 
the few good recommendations....see below:

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
FROM: dpbsmith@xxxxxxxxxxxxx (Daniel P. B. Smith)
SUBJECT: Re: Optics of human eye
DATE: Sun, 5 Sep 1999 09:56:32 GMT
ORGANIZATION: The World Public Access UNIX, Brookline, MA
NEWSGROUPS: sci.optics

"Alex Ch." <alans@xxxxxxxxxxxxxx> asked:
>P.S. Does anybody know a source for detailed description of an ocular optics
>for a human eye? The more I am in optics, the less I understand how I can
>see this world so clearly...

Anyone who knows something more current, please chime in... A good
starting point is (don't laugh) Helmholtz's _Treatise on Physiological
Optics_, which is available in English translation as a Dover reprint (two
volumes, hardbound)  It's not quite as old as you might think because the
editor updated it extensively, so it basically is current up to 1924.
It is fascinating because Helmholtz went into _every_ aspect of vision and
his interests were wide-ranging.  And it has that wonderful
nineteenth-century _tinkering_ style and if you're any sort of amateur
scientist it will send you off into the basement to dig into your supply
of Edmund lenses and mirrors trying things.  It has all sorts of pictures
of the subjective appearance of entoptic phenomena.  Haidinger's brushes,
Maxwell's spot, etc.--it's all there.

Helmholtz was quite aware of, and interested in the question of how we
experience such clear vision from such an optically imperfect system.

It has quite a bit of _quantitative_ information on the optical system of
the eye.  There's probably more available now.  His book has quite an
awareness of the fact that there is no such thing as "_the_ eye"--there's
a lot of individual variability, which I think tends to get swept under
the rug a bit.  (I've seen dozens of graphs showing the CIE colorimetric
data for the "standard observer" but I don't recall seeing a single one
that indicates the normal range of variation within people with _normal_
color vision, for example).

-- 
Daniel P. B. Smith
dpbsmith@xxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxx

>  Try this experiment, to shield your eye from unfiltered light,
> attach a piece of black card/paper around your R72 filter to form
> a short tube, and look through the filter at some green foliage
> in bright sunlight. It will take a few seconds for your eye to
> adjust, but you will be able to see a faint infrared woodeffect
> image of the foliage, you are seeing visible near-infrared light.
>  I was amazed that it was possible to see this, so I would suggest
> that the filter is working and you are seeing an infrared image
> of your light bulb filament.

The problem is that the Wood-effect starts already below the visible 
limit, at 695nm. That is why it can even be recorded with SFX, which 
is by no means IR-sensitive at all (limit 740nm, peaking at 720nm).
The best 'color' to see the Wood-effect with the naked eye is #88 
(not #88A as sold last by Kodak, which is just beyond the visible limit). 

--                 
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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