jbm@eos.UUCP (Jeffrey Mulligan) (05/10/88)
+ But what makes me curious is that every "black light" I've ever seen + has a peculiar quality to it that I never see in any other kind of + illumination. Hard to describe but it looks very specular, somewhat + like laser illumination of normal surfaces, and it always looks a little + fuzzy, possibly as if it were out of focus. When I ask other people if + they perceive anything like this, they look at me funny. Ultraviolet radiation causes the lens of the eye to flouresce. This would produce a diffuse illumination of the entire retinal image, but the effect would probably be more of a soft-focus effect, (sharp edges with a fuzzy overlay) rather than out and out blurring. -- Jeff Mulligan (jbm@ames-aurora.arpa) NASA/Ames Research Ctr., Mail Stop 239-3, Moffet Field CA, 94035 (415) 694-5150
greg@bilbo (Greg Wageman) (05/12/88)
In article <685@eos.UUCP> jbm@eos.UUCP (Jeffrey Mulligan) writes: >+ But what makes me curious is that every "black light" I've ever seen >+ has a peculiar quality to it that I never see in any other kind of >+ illumination. Hard to describe but it looks very specular, somewhat >+ like laser illumination of normal surfaces, and it always looks a little >+ fuzzy, possibly as if it were out of focus. When I ask other people if >+ they perceive anything like this, they look at me funny. > >Ultraviolet radiation causes the lens of the eye to flouresce. >This would produce a diffuse illumination of the entire retinal image, >but the effect would probably be more of a soft-focus effect, >(sharp edges with a fuzzy overlay) rather than out and out blurring. The above may very well be true, but... Different wavelengths of light also refract to different degrees through the same material (e. g. a prism, or the lens of your eye.) Your eye does what it normally does to bring an image into focus under wide-spectrum lighting conditions. But since "UV" is at the extreme end of the visible spectrum (actually what you are seeing is the extreme deep violet visible portion), its refraction will be far enough from the correct focal point that it will indeed be out of focus. Greg Wageman ARPA: greg%sentry@spar.slb.com Schlumberger Technologies BIX: gwage 1601 Technology Drive CIS: 74016,352 San Jose, CA 95110 GEnie: GWAGEMAN (408) 437-5198 UUCP: ...!decwrl!spar!sentry!greg ------------------ The opinions expressed herein are solely the responsibility of the author.
jbm@eos.UUCP (05/13/88)
From article <230@snjsn1.SJ.ATE.SLB.COM>, by greg@bilbo (Greg Wageman): > In article <685@eos.UUCP> jbm@eos.UUCP (Jeffrey Mulligan) writes: >> >>Ultraviolet radiation causes the lens of the eye to flouresce. >>This would produce a diffuse illumination of the entire retinal image, >>but the effect would probably be more of a soft-focus effect, >>(sharp edges with a fuzzy overlay) rather than out and out blurring. > > The above may very well be true, but... You bet your booties it's true! I quote from page 116 Wyszecki & Stiles, "Color Science", 2nd ed., John Wiley & Sons 1982: "The flourescence of the human eye lens is caused by ultraviolet radiant energy (lambda < 400 nm). It produces a general veil of bluish light over the retina. The spectral composition of the flourescent light probably agrees with the spectral distributions - all similar - determined for the eye lenses of sheep, rabbit, and ox, by LeGrand (1948)." > > ... But since "UV" is at the extreme end > of the visible spectrum (actually what you are seeing is the extreme > deep violet visible portion), its refraction will be far enough from > the correct focal point that it will indeed be out of focus. > The lens absorbs UV, unlike IR which can be seen by simply jacking up the power to compensate for the lower sensitivity of the visual pigments. Continuing the above quote: "The retina is also flourescent to ultraviolet and possibly to short-wavelength visible light, but in the normal eye, absorption in the eye lens removes most of the exciting radiant energy before it can reach the retina. Aphakic observers (eye lens removed) are able to see stimuli of wavelengths much deeper in the ultraviolet than are normals, the color seen in the range of 360 to 310 nm being blue, not violet (Gaydon, 1938). This change of color may be the visual response to a mixture of bluish-green flourescent radiant flux with the original ultraviolet stimulus; however, this is controversial." Greg's point about chromatic aberration is certainly valid in the visible range, but it is interesting that this is not usually noticeable. There is a nice demonstration of this at the Exploratorium in San Francisco: They have an array of pinholes illuminated from behind with white light. Most people see a bunch of white spots. When the same spots are observed through a purple filter (which transmits only red and violet), you see a red dot surrounded by a bluish cloud. (I myself see a cross made up of a red and a blue member due to my astigmatism.) The point is that the blue component of the white light is just as blurred when it looks white, but that the brain compensates for the chromatic fringes present at the edges of white objects. -- Jeff Mulligan (jbm@ames-aurora.arpa) NASA/Ames Research Ctr., Mail Stop 239-3, Moffet Field CA, 94035 (415) 694-5150
awpaeth@watcgl.waterloo.edu (Alan W. Paeth) (05/15/88)
(re: discussions on the world as seen by people lacking the eye's crystalline
lens and on the ability to focus on the blue end of the spectrum).
I've often wondered what cataract viewers see, and what we normal folk are
missing -- off in the near UV where bees see pollen and such. Then I came
across this month's issue of "Sky and Telescope". The author of their deep
sky splendors column has had such surgery and boasted (I felt) that it added
some violets to certain nebula (The Crab?). He removes his glasses and any
eyepices and gets "prime focus" projection directly onto his retina!
Presumably he is using a reflecting telescope so that the image plane for UV
coincides with the visible.
The previous poster referenced Wysezeki and Stiles on UV vision and lens
flourescence. Two months ago I had to opportunity to visit the CNRC (Canadian
National Research Council) optics lab and colorimetry section, and saw
(through) the special glasses Wysezeki designed which provide achromatic
correction for a standard observer. These are "no power" chromatic correcting
lenses (afocal triplets, I also viewed through a seven element afocal
"eyepiece"). As near as I could tell with my 20/15 corrected vision, the
lenses did absolutely nothing.
This was Wysezeki's previous conclusion (while still alive); he had considered
marketing them. But note, I've seen JS&A (those gizmo-widget folks) advertise
special "minus blue" specs which are supposed to significantly improve contrast.
* They won't get any of my money! *
Incidentally, the lens prescription appears in that volume, together with the
aberration chart which puts people a good two or three diopters out in the far
blue. I've occasionally seen the effect -- it is maxmized when looking at blue
lettering on a dark surround viewed at infinity (closer than about 6 ft. and
your eye can accomodate). The most memorable example was blue computer graphics
lettering done in a 35mm slide presentation, but in all fairness, the slide was
designed to illustrate the effect.
/Alan Paeth
Computer Graphics Laboratory
University of Waterloojtk@mordor.s1.gov (Jordan Kare) (05/17/88)
In article <4433@watcgl.waterloo.edu> awpaeth@watcgl.waterloo.edu (Alan W. Paeth) writes: >(re: discussions on the world as seen by people lacking the eye's crystalline >lens and on the ability to focus on the blue end of the spectrum). > >Incidentally, ... the >aberration chart ... puts people a good two or three diopters out in the far >blue. I've occasionally seen the effect -- it is maxmized when looking at blue >lettering on a dark surround viewed at infinity (closer than about 6 ft. and >your eye can accomodate). The most memorable example was blue computer graphics >lettering done in a 35mm slide presentation, but in all fairness, the slide was >designed to illustrate the effect. In El Cerrito, CA, there is a building on Fairmont Ave. which has a large (several foot high) sign composed of internally lit letters. The letters are deep blue, and the sign as a whole is visible for several blocks. However, it is also completely illegible, and (at least to my eyes, which are beginning to have some distance vision problems as I age, although I've never worn glasses) appears as a large blue blur until you get very close, whereupon it finally resolves into the words EYE CENTER :-) Jordin (The Eternal Optometrist) Kare jtk@mordor.UUCP jtk@mordor.s1.gov