laser pointers

"Uncle Al" wrote in message
...

Bug eye rhabdomere's don't focus an image, they assemble pixels.
Lenses and retinas do focus an image.

I was wondering if it was something like that. Once again, you prove
helpful!
Thanks.

On Tue, 5 Aug 2003, Jeremy wrote:

"Uncle Al" wrote in message
...

Bug eye rhabdomere's don't focus an image, they assemble pixels.
Lenses and retinas do focus an image.

I was wondering if it was something like that. Once again, you prove
helpful!
Thanks.

I see that Smith & King "Optics & Photonics" has a nice little section on
bug eyes. Check it out. It's also likely that bug eyes tolerate higher
light levels. No eyelids, so they need to be capable of staring at the sun
for hours on end.

--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html

wrote in message
...
In the absence of a lens, the light levels should be
manageable. It
is the lens that creates the problem, in this case.


Yes, and the worse your eyesight is, the safer you are
around a laser. Provided you're not wearing corrective
lenses, ala Hubble.

It's the same principle: you don't want a very concentrated
image on your retina, burning out a tiny bit of it.

You don't need coherent light to do this, of course. People
have fried their retinas looking at solar eclipses and
welding arcs. In both cases the problem is the same: total
light is low enough to allow you to keep looking without
papillary constriction or pain), but that light is of high
intensity over a small area of that field of view (so your
retina just there gets zapped).

Lasers are more dangerous per amount of light output because
the coherance of the beam makes it focusable to a smaller
point with a perfect lens. If you look at the sun, the best
even a perfect eye can do is project an image of a sun on
your retina, and that has a diameter. Even the bit you see
on the arc of a solar eclipse has an area. The light
intensity is high enough to fry you even over that area, but
a laser of the same light output would be worse.

Some numbers. If your pupil were 1 cm^2 you'd get about 100
mW into it from the sun. If you're looking at 25% of an
eclipse that's 25 mW. That power would be a fairly
dangerous laser, and 5 mW is the most they allow for
pointers and such. Hmmm. Looking at the numbers I'm
surprised people do as much damage from eclipses as they do.
10% of an eclipse, which is where your pupil really *would*
be dilated to 1 cm^2, would only be 10 mW. Okay, in THEORY
lasers are worse.

SBH

On Tue, 5 Aug 2003 wrote:

Timo Nieminen writes:

It's also likely that bug eyes tolerate higher
light levels. No eyelids, so they need to be capable of staring at the sun
for hours on end.

In the absence of a lens, the light levels should be manageable. It
is the lens that creates the problem, in this case.

Lack of lenses helps, though some bug eyes use waveguides to concentrate
incident light onto a photoreceptor. A 1mW beam with a 1mm^2 spot size has
about the same irradiance as sunlight, so the bug should be OK. A lens
would give a diffraction limited spot of the beam vs an image of the solar
disk, so the same comparison isn't so good for us.

We had a fun laser safety course, complete with the usual horror stories,
such as the fellow who notices the audible "pop" as the surface of his
retina is cooked.

--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html

In article , Timo Nieminen writes:
On Tue, 5 Aug 2003 wrote:

Timo Nieminen writes:

It's also likely that bug eyes tolerate higher
light levels. No eyelids, so they need to be capable of staring at the sun
for hours on end.

In the absence of a lens, the light levels should be manageable. It
is the lens that creates the problem, in this case.

Lack of lenses helps, though some bug eyes use waveguides to concentrate
incident light onto a photoreceptor. A 1mW beam with a 1mm^2 spot size has
about the same irradiance as sunlight, so the bug should be OK. A lens
would give a diffraction limited spot of the beam vs an image of the solar
disk, so the same comparison isn't so good for us.

Yes, indeed. Though, as Steve mentioned, the worse your eyes are, the
better off you're.

We had a fun laser safety course, complete with the usual horror stories,
such as the fellow who notices the audible "pop" as the surface of his
retina is cooked.

Uggh.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

wrote in message ...
In article , Timo Nieminen writes:
On Tue, 5 Aug 2003, Jeremy wrote:

"Uncle Al" wrote in message
...

Bug eye rhabdomere's don't focus an image, they assemble pixels.
Lenses and retinas do focus an image.

I was wondering if it was something like that. Once again, you prove
helpful!
Thanks.

I see that Smith & King "Optics & Photonics" has a nice little section on
bug eyes. Check it out. It's also likely that bug eyes tolerate higher
light levels. No eyelids, so they need to be capable of staring at the sun
for hours on end.

In the absence of a lens, the light levels should be manageable. It
is the lens that creates the problem, in this case.

Actually, each facet of an insect's eye has a small lens.

Paul Cardinale

Paul Cardinale wrote:

wrote in message ...
In article , Timo Nieminen writes:
On Tue, 5 Aug 2003, Jeremy wrote:

"Uncle Al" wrote in message
...

Bug eye rhabdomere's don't focus an image, they assemble pixels.
Lenses and retinas do focus an image.

I was wondering if it was something like that. Once again, you prove
helpful!
Thanks.

I see that Smith & King "Optics & Photonics" has a nice little section on
bug eyes. Check it out. It's also likely that bug eyes tolerate higher
light levels. No eyelids, so they need to be capable of staring at the sun
for hours on end.

In the absence of a lens, the light levels should be manageable. It
is the lens that creates the problem, in this case.

Actually, each facet of an insect's eye has a small lens.

Rhabdomeres are not imaging elements. They concentrate light without
a focus (e.g., caustics). In principle a clean laser can be focused
to a primary spot 1/2 its wavelength in diameter (hence pinhole
spatial filtering). A non-imaging element would not concentrate
energy like an imaging element.

Besides, torturing insects is best done with straight pins and
D-cells.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!

In sci.physics, Uncle Al

wrote
on Thu, 07 Aug 2003 08:35:06 -0700
:
Paul Cardinale wrote:

[snip for brevity]

Actually, each facet of an insect's eye has a small lens.

Rhabdomeres are not imaging elements. They concentrate light without
a focus (e.g., caustics). In principle a clean laser can be focused
to a primary spot 1/2 its wavelength in diameter (hence pinhole
spatial filtering). A non-imaging element would not concentrate
energy like an imaging element.

Besides, torturing insects is best done with straight pins and
D-cells.


Dare I ask how you spent your youth? :-) ;-) :-)

--
#191,
It's still legal to go .sigless.

Uncle Al wrote in message ...
Paul Cardinale wrote:

wrote in message ...
In article , Timo Nieminen writes:
On Tue, 5 Aug 2003, Jeremy wrote:

"Uncle Al" wrote in message
...

Bug eye rhabdomere's don't focus an image, they assemble pixels.
Lenses and retinas do focus an image.

I was wondering if it was something like that. Once again, you prove
helpful!
Thanks.

I see that Smith & King "Optics & Photonics" has a nice little section on
bug eyes. Check it out. It's also likely that bug eyes tolerate higher
light levels. No eyelids, so they need to be capable of staring at the sun
for hours on end.

In the absence of a lens, the light levels should be manageable. It
is the lens that creates the problem, in this case.

Actually, each facet of an insect's eye has a small lens.

Rhabdomeres are not imaging elements.

Of course.

They concentrate light without
a focus (e.g., caustics).

Do you mean that the sensory elements are not at the foci of their lenses,
or that the lenses do not have well defined foci?

In principle a clean laser can be focused
to a primary spot 1/2 its wavelength in diameter

How long would it have to be to be 'clean'?

Paul Cardinale

Paul Cardinale wrote:

Uncle Al wrote in message ...
Paul Cardinale wrote:

wrote in message ...
In article , Timo Nieminen writes:
On Tue, 5 Aug 2003, Jeremy wrote:

"Uncle Al" wrote in message
...

Bug eye rhabdomere's don't focus an image, they assemble pixels.
Lenses and retinas do focus an image.

I was wondering if it was something like that. Once again, you prove
helpful!
Thanks.

I see that Smith & King "Optics & Photonics" has a nice little section on
bug eyes. Check it out. It's also likely that bug eyes tolerate higher
light levels. No eyelids, so they need to be capable of staring at the sun
for hours on end.

In the absence of a lens, the light levels should be manageable. It
is the lens that creates the problem, in this case.

Actually, each facet of an insect's eye has a small lens.

Rhabdomeres are not imaging elements.

Of course.

They concentrate light without
a focus (e.g., caustics).

Do you mean that the sensory elements are not at the foci of their lenses,
or that the lenses do not have well defined foci?

Look up the anatomy. The assembly is more of a waveguide than an
imagining optic.

http://soma.npa.uiuc.edu/courses/bio303/Ch11b.html

In principle a clean laser can be focused
to a primary spot 1/2 its wavelength in diameter

How long would it have to be to be 'clean'?

Coherent in time and space, TEM_00. You'd want a very 3X *short*
laser to exclude alternate modes.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!