More on retina and vision...

[Jan Panteltje]

On a sunny day (Mon, 31 Oct 2022 12:29:35 -0700) it happened John Larkin
<jlarkin@highland_atwork_technology.com> wrote in
<ob80mh5p0lspeqo4vn5ort1e2162ert132@4ax.com>:

I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution,

A very short pulse would have many harmonics, but I do not see that as a
usable spectrum, the shorter the pulse the more the harmonics are apart?
And possibly outside the usable spectrum?

but an
incoherent red LED is a lot cheaper.

Yes redish noise ;-)

 

[John Larkin]

On Tue, 01 Nov 2022 04:20:25 GMT, Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 12:29:35 -0700) it happened John Larkin
jlarkin@highland_atwork_technology.com> wrote in
ob80mh5p0lspeqo4vn5ort1e2162ert132@4ax.com>:

I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution,

A very short pulse would have many harmonics, but I do not see that as a
usable spectrum, the shorter the pulse the more the harmonics are apart?
And possibly outside the usable spectrum?

A short sinewave burst is wideband about the nominal sine center
frequency. It\'s not a matter of harmonics.

but an
incoherent red LED is a lot cheaper.

Yes redish noise ;-)

Exactly.

 

[Jan Panteltje]

On a sunny day (Mon, 31 Oct 2022 22:05:35 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<n5a1mh1iirdi58744phjderhb9ri032p1a@4ax.com>:

On Tue, 01 Nov 2022 04:20:25 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 12:29:35 -0700) it happened John Larkin
jlarkin@highland_atwork_technology.com> wrote in
ob80mh5p0lspeqo4vn5ort1e2162ert132@4ax.com>:

I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution,

A very short pulse would have many harmonics, but I do not see that as a
usable spectrum, the shorter the pulse the more the harmonics are apart?
And possibly outside the usable spectrum?



A short sinewave burst is wideband about the nominal sine center
frequency. It\'s not a matter of harmonics.

A pure sinewave burst that starts at zero and ends at zero with length t
can be compared to an amplitude modulated signal (as in radio)
and should have, apart from the main carrier, 2 sidebands -1/t and +1/t apart
|
| | |
AM signal
?

If the sinewave pulse is distorted somehow you will get more spectral components,
Also if the frequency is changing during the presence of that pulse (FM spectrum).

?

 

[Jeroen Belleman]

On 2022-11-01 06:31, Jan Panteltje wrote:

On a sunny day (Mon, 31 Oct 2022 22:05:35 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
n5a1mh1iirdi58744phjderhb9ri032p1a@4ax.com>:

On Tue, 01 Nov 2022 04:20:25 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 12:29:35 -0700) it happened John Larkin
jlarkin@highland_atwork_technology.com> wrote in
ob80mh5p0lspeqo4vn5ort1e2162ert132@4ax.com>:

I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution,

A very short pulse would have many harmonics, but I do not see that as a
usable spectrum, the shorter the pulse the more the harmonics are apart?
And possibly outside the usable spectrum?



A short sinewave burst is wideband about the nominal sine center
frequency. It\'s not a matter of harmonics.

A pure sinewave burst that starts at zero and ends at zero with length t
can be compared to an amplitude modulated signal (as in radio)
and should have, apart from the main carrier, 2 sidebands -1/t and +1/t apart
|
| | |
AM signal
?

If the envelope of the sinewave burst is a pulse, then the AM signal
will have the bandwidth of that pulse. For example, if you modulate
the carrier with a Gaussian, say, the modulated signal spectrum will
have a Gaussian shape centred on the carrier.

Jeroen Belleman

 

[Jan Panteltje]

On a sunny day (Tue, 01 Nov 2022 10:55:21 +0100) it happened Jeroen Belleman
<jeroen@nospam.please> wrote in <tjqqe8$439$1@gioia.aioe.org>:

On 2022-11-01 06:31, Jan Panteltje wrote:
On a sunny day (Mon, 31 Oct 2022 22:05:35 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
n5a1mh1iirdi58744phjderhb9ri032p1a@4ax.com>:

On Tue, 01 Nov 2022 04:20:25 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 12:29:35 -0700) it happened John Larkin
jlarkin@highland_atwork_technology.com> wrote in
ob80mh5p0lspeqo4vn5ort1e2162ert132@4ax.com>:

I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution,

A very short pulse would have many harmonics, but I do not see that as a
usable spectrum, the shorter the pulse the more the harmonics are apart?
And possibly outside the usable spectrum?



A short sinewave burst is wideband about the nominal sine center
frequency. It\'s not a matter of harmonics.

A pure sinewave burst that starts at zero and ends at zero with length t
can be compared to an amplitude modulated signal (as in radio)
and should have, apart from the main carrier, 2 sidebands -1/t and +1/t apart
|
| | |
AM signal
?

If the envelope of the sinewave burst is a pulse, then the AM signal
will have the bandwidth of that pulse. For example, if you modulate
the carrier with a Gaussian, say, the modulated signal spectrum will
have a Gaussian shape centred on the carrier.

Jeroen Belleman

Sure.

 

[John Larkin]

On Tue, 01 Nov 2022 05:31:04 GMT, Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 22:05:35 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
n5a1mh1iirdi58744phjderhb9ri032p1a@4ax.com>:

On Tue, 01 Nov 2022 04:20:25 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 12:29:35 -0700) it happened John Larkin
jlarkin@highland_atwork_technology.com> wrote in
ob80mh5p0lspeqo4vn5ort1e2162ert132@4ax.com>:

I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution,

A very short pulse would have many harmonics, but I do not see that as a
usable spectrum, the shorter the pulse the more the harmonics are apart?
And possibly outside the usable spectrum?



A short sinewave burst is wideband about the nominal sine center
frequency. It\'s not a matter of harmonics.

A pure sinewave burst that starts at zero and ends at zero with length t
can be compared to an amplitude modulated signal (as in radio)
and should have, apart from the main carrier, 2 sidebands -1/t and +1/t apart
|
| | |
AM signal
?

If the sinewave pulse is distorted somehow you will get more spectral components,
Also if the frequency is changing during the presence of that pulse (FM spectrum).

?

Exactly. AM produces sidebands alongside the carrier, not harmonics.
The more agressive the modulation waveform, the wider the sideband
spread.

A perfect laser beam is a perfect sine wave with infinite
autocorrelation distance. Modulate it with a fast gaussian pulse, and
you get a soft tone burst with sidebands and a short correlation
distance. Which is why radars don\'t use sine waves to measure
distance; too many ambiguities.

There are attosecond lasers that make just a few cycles of optical
sine wave. An incoherent LED is a cheap option.

One of the great revelations in my life was a 1-semister EE course at
Tulane, Signals and Systems. I should write an essay or maybe a book
about S+S. It\'s very important.

This is OK,

https://www.amazon.com/Signals-Systems-Dummies-Mark-Wickert/dp/111847581X/ref=sr_1_1?crid=104VWOY2F5L7S&keywords=signals+and+systems+for+dummies&qid=1667305652&qu=eyJxc2MiOiIwLjQxIiwicXNhIjoiMC4xOSIsInFzcCI6IjAuMzAifQ%3D%3D&sprefix=signals+and+systems%2Caps%2C154&sr=8-1

but is still equation-heavy.

 

[Anthony William Sloman]

On Tuesday, November 1, 2022 at 11:34:57 PM UTC+11, John Larkin wrote:

On Tue, 01 Nov 2022 05:31:04 GMT, Jan Panteltje <pNaonSt...@yahoo.com> wrote:
On a sunny day (Mon, 31 Oct 2022 22:05:35 -0700) it happened John Larkin <jla...@highlandSNIPMEtechnology.com> wrote in <n5a1mh1iirdi58744...@4ax.com>:
On Tue, 01 Nov 2022 04:20:25 GMT, Jan Panteltje <pNaonSt...@yahoo.com> wrote:
On a sunny day (Mon, 31 Oct 2022 12:29:35 -0700) it happened John Larkin <jlarkin@highland_atwork_technology.com> wrote in=<ob80mh5p0lspeqo4v....@4ax.com>:

I guess that a femtosecond monochromatic pulse would have the same effect, wideband optical spectrum and good distance resolution,

A very short pulse would have many harmonics, but I do not see that as a usable spectrum, the shorter the pulse the more the harmonics are apart?
And possibly outside the usable spectrum?

A short sinewave burst is wideband about the nominal sine center frequency. It\'s not a matter of harmonics.

A pure sinewave burst that starts at zero and ends at zero with length t can be compared to an amplitude modulated signal (as in radio)
and should have, apart from the main carrier, 2 sidebands -1/t and +1/t apart.

One has to wonder why. The process of gating it down to a finite width is multiplying by a narrow pulse which has all frequencies up to with width of the pulse. You certainly don\'t get just two sidebands - that is what you get when you multiply two pure sine waves.

<snip>

Exactly. AM produces sidebands alongside the carrier, not harmonics.
The more aggressive the modulation waveform, the wider the sideband spread,

I wonder what John means by \"aggressive\"?

The side-bands are spread by the modulation frequency, The higher the frequency of the modulating sine wave, the the further the two sidebands are above and below the carrier frequency

A perfect laser beam is a perfect sine wave with infinite
autocorrelation distance. Modulate it with a fast gaussian pulse, and
you get a soft tone burst with sidebands and a short correlation
distance.

Lots of sidebands, because a fast guassian pulse has a very wide fourier transform - lots of frequencies, up to the limit set by the width of the pulse, and down to the limit set by its repetition rate,

Which is why radars don\'t use sine waves to measure distance; too many ambiguities.

There are attosecond lasers that make just a few cycles of optical
sine wave. An incoherent LED is a cheap option.

One of the great revelations in my life was a 1-semister EE course at Tulane, Signals and Systems. I should write an essay or maybe a book about S+S. It\'s very important.

Somebody who knew how to spell semester might be a better candidate, as would somebody who knew something about the subject.

This is OK,

https://www.amazon.com/Signals-Systems-Dummies-Mark-Wickert/dp/111847581X/ref=sr_1_1?crid=104VWOY2F5L7S&keywords=signals+and+systems+for+dummies&qid=1667305652&qu=eyJxc2MiOiIwLjQxIiwicXNhIjoiMC4xOSIsInFzcCI6IjAuMzAifQ%3D%3D&sprefix=signals+and+systems%2Caps%2C154&sr=8-1

but is still equation-heavy.

It clearly didn\'t tell John as much as he needed to learn.

--
Bill Sloman, Sydney

 

[Jan Panteltje]

On a sunny day (Tue, 01 Nov 2022 05:34:45 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<go32mhl0o1ccss9qqvfscre5ssb03hh8st@4ax.com>:

On Tue, 01 Nov 2022 05:31:04 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 22:05:35 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
n5a1mh1iirdi58744phjderhb9ri032p1a@4ax.com>:

On Tue, 01 Nov 2022 04:20:25 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 12:29:35 -0700) it happened John Larkin
jlarkin@highland_atwork_technology.com> wrote in
ob80mh5p0lspeqo4vn5ort1e2162ert132@4ax.com>:

I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution,

A very short pulse would have many harmonics, but I do not see that as a
usable spectrum, the shorter the pulse the more the harmonics are apart?
And possibly outside the usable spectrum?



A short sinewave burst is wideband about the nominal sine center
frequency. It\'s not a matter of harmonics.

A pure sinewave burst that starts at zero and ends at zero with length t
can be compared to an amplitude modulated signal (as in radio)
and should have, apart from the main carrier, 2 sidebands -1/t and +1/t apart
|
| | |
AM signal
?

If the sinewave pulse is distorted somehow you will get more spectral components,
Also if the frequency is changing during the presence of that pulse (FM spectrum).

?


Exactly. AM produces sidebands alongside the carrier, not harmonics.
The more agressive the modulation waveform, the wider the sideband
spread.

A perfect laser beam is a perfect sine wave with infinite
autocorrelation distance. Modulate it with a fast gaussian pulse, and
you get a soft tone burst with sidebands and a short correlation
distance. Which is why radars don\'t use sine waves to measure
distance; too many ambiguities.

There are attosecond lasers that make just a few cycles of optical
sine wave. An incoherent LED is a cheap option.

Jeroen already gave the correct answer, modulate with a gaussian.
bit different from your \'femtosecond monochromatic pulse\'

One of the great revelations in my life was a 1-semister EE course at
Tulane, Signals and Systems. I should write an essay or maybe a book
about S+S. It\'s very important.

This is OK,

https://www.amazon.com/Signals-Systems-Dummies-Mark-Wickert/dp/111847581X/ref=sr_1_1?crid=104VWOY2F5L7S&keywords=signals+and+syst
ems+for+dummies&qid=1667305652&qu=eyJxc2MiOiIwLjQxIiwicXNhIjoiMC4xOSIsInFzcCI6IjAuMzAifQ%3D%3D&sprefix=signals+and+systems%2Caps
%2C154&sr=8-1

but is still equation-heavy.

EEEH Python snake language BAD
Radio and teefee is all about spectra, even the old US NTSC color system is a very interesting thing.

I have heard of maaz but am just a neural net,

 

[John Larkin]

On Tue, 01 Nov 2022 13:25:59 GMT, Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Tue, 01 Nov 2022 05:34:45 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
go32mhl0o1ccss9qqvfscre5ssb03hh8st@4ax.com>:

On Tue, 01 Nov 2022 05:31:04 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 22:05:35 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
n5a1mh1iirdi58744phjderhb9ri032p1a@4ax.com>:

On Tue, 01 Nov 2022 04:20:25 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Mon, 31 Oct 2022 12:29:35 -0700) it happened John Larkin
jlarkin@highland_atwork_technology.com> wrote in
ob80mh5p0lspeqo4vn5ort1e2162ert132@4ax.com>:

I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution,

A very short pulse would have many harmonics, but I do not see that as a
usable spectrum, the shorter the pulse the more the harmonics are apart?
And possibly outside the usable spectrum?



A short sinewave burst is wideband about the nominal sine center
frequency. It\'s not a matter of harmonics.

A pure sinewave burst that starts at zero and ends at zero with length t
can be compared to an amplitude modulated signal (as in radio)
and should have, apart from the main carrier, 2 sidebands -1/t and +1/t apart
|
| | |
AM signal
?

If the sinewave pulse is distorted somehow you will get more spectral components,
Also if the frequency is changing during the presence of that pulse (FM spectrum).

?


Exactly. AM produces sidebands alongside the carrier, not harmonics.
The more agressive the modulation waveform, the wider the sideband
spread.

A perfect laser beam is a perfect sine wave with infinite
autocorrelation distance. Modulate it with a fast gaussian pulse, and
you get a soft tone burst with sidebands and a short correlation
distance. Which is why radars don\'t use sine waves to measure
distance; too many ambiguities.

There are attosecond lasers that make just a few cycles of optical
sine wave. An incoherent LED is a cheap option.

Jeroen already gave the correct answer, modulate with a gaussian.

I think someone else may have suggested that too.

>bit different from your \'femtosecond monochromatic pulse\'

Maybe not.

 

[John Walliker]

On Tuesday, 1 November 2022 at 17:48:35 UTC, John Larkin wrote:

A perfect laser beam is a perfect sine wave with infinite
autocorrelation distance. Modulate it with a fast gaussian pulse, and
you get a soft tone burst with sidebands and a short correlation
distance. Which is why radars don\'t use sine waves to measure
distance; too many ambiguities.

Some do - almost. Chirp radars use a frequency swept sinewave.

John

 

[Jeroen Belleman]

On 2022-11-01 19:31, John Walliker wrote:

On Tuesday, 1 November 2022 at 17:48:35 UTC, John Larkin wrote:

A perfect laser beam is a perfect sine wave with infinite
autocorrelation distance. Modulate it with a fast gaussian pulse, and
you get a soft tone burst with sidebands and a short correlation
distance. Which is why radars don\'t use sine waves to measure
distance; too many ambiguities.

Some do - almost. Chirp radars use a frequency swept sinewave.

John

Sure, but the autocorrelation function of that chirp is a narrow
spike, which is what you need to get good range resolution.

Jeroen Belleman

 

[Joe Gwinn]

On Tue, 01 Nov 2022 19:39:47 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:

On 2022-11-01 19:31, John Walliker wrote:
On Tuesday, 1 November 2022 at 17:48:35 UTC, John Larkin wrote:

A perfect laser beam is a perfect sine wave with infinite
autocorrelation distance. Modulate it with a fast gaussian pulse, and
you get a soft tone burst with sidebands and a short correlation
distance. Which is why radars don\'t use sine waves to measure
distance; too many ambiguities.

Some do - almost. Chirp radars use a frequency swept sinewave.

John


Sure, but the autocorrelation function of that chirp is a narrow
spike, which is what you need to get good range resolution.

Then there is FMCW, originally for radar altimeters in airplanes.

..<https://en.wikipedia.org/wiki/Continuous-wave_radar>

Joe Gwinn

 

[John Larkin]

On Mon, 31 Oct 2022 12:29:35 -0700, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

On Mon, 31 Oct 2022 12:21:16 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Sun, 30 Oct 2022 06:18:57 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Sat, 29 Oct 2022 11:47:39 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
r7sqlhpppp3n8fhhs5nn9hf16tqddb4vcg@4ax.com>:

On Sat, 29 Oct 2022 17:25:34 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Sat, 29 Oct 2022 07:34:47 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
qrdqlhpor5v5h642dr8ida0lqjodp3gdfk@4ax.com>:

On Sat, 29 Oct 2022 04:59:56 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

https://www.sciencedaily.com/releases/2022/10/221027123919.htm
https://www.rockefeller.edu/news/33135-fruit-flies-move-their-retinas-much-like-humans-move-their-eyes/

Makes me wonder if we will get vibrating camera sensors, maybe using piezos to
move the CCD ?

Speaking of retinas...

https://www.dropbox.com/s/z4kym11g2qvlgei/Retina_Repair_2022.jpg?raw=1

We don\'t know exactly why the left eye developed a macular hole; they
do that sometimes.

Look into a laser?

Not even a laser. One looks into a lens and sees some blue rectangles
for a few seconds. LEDs, not lasers.



The good news is that it can be mostly fixed. The guy who did it is a
genius with a very steady hand.

The tomography is amazing. Just a few seconds looking at some blue
lights.

Yes, looks almost better now than the right eye!

It does. The right eye is normal, a little puckered around the macula.
The treatment is for the doc to peel away the top two layers of cells
in a big patch of the retina, which relieves stress and lets the hole
close. Done by hand. With tweezers. It was interesting, a half hour of
wild light show.


What exactly does the blue light do?

Don\'t know. I should look it up, \"Optical coherence tomography of
macular holes.\" The original resolution is much better than what I
posted, which was scanned from a paper report.

Amazing.

Here\'s a really good tomograph.

https://retinaassociatesofgreaterphiladelphia.com/wp-content/uploads/2021/07/STAGE-3-MAC-HOLE-WITH-PSEUDO-OPERCULUM-CROPPED-WITH-
RA.jpg

You can see the vitreus humor pulled back from the retina, and a bit
that it tore away.

https://en.wikipedia.org/wiki/Optical_coherence_tomography

Thank you very much for the links
Always learning!
Very impressive that wikipedia link!

It\'s interesting to think of making a split-beam interferometer with
wideband light. You get good interference over a very short range of
distances, as opposed to periodic interferance over a wide range with
long-coherence light.

I did see a red line sweep top to bottom when they did the scan.


I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution, but an
incoherent red LED is a lot cheaper.

I knew a guy who patented an HF navigation system sort of like Loran,
but the transmitters sent pseudo-random modulated RF, the idea being
that a cross-correlating receiver could distinguish the ground wave
and ignore ionosphere paths. Same idea, really.

Sadly, he invented that just as GPS was ramping up.

 

[Gerhard Hoffmann]

Am 05.11.22 um 01:04 schrieb John Larkin:

On Mon, 31 Oct 2022 12:29:35 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Mon, 31 Oct 2022 12:21:16 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Sun, 30 Oct 2022 06:18:57 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Sat, 29 Oct 2022 11:47:39 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
r7sqlhpppp3n8fhhs5nn9hf16tqddb4vcg@4ax.com>:

On Sat, 29 Oct 2022 17:25:34 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Sat, 29 Oct 2022 07:34:47 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
qrdqlhpor5v5h642dr8ida0lqjodp3gdfk@4ax.com>:

On Sat, 29 Oct 2022 04:59:56 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

https://www.sciencedaily.com/releases/2022/10/221027123919.htm
https://www.rockefeller.edu/news/33135-fruit-flies-move-their-retinas-much-like-humans-move-their-eyes/

Makes me wonder if we will get vibrating camera sensors, maybe using piezos to
move the CCD ?

Speaking of retinas...

https://www.dropbox.com/s/z4kym11g2qvlgei/Retina_Repair_2022.jpg?raw=1

We don\'t know exactly why the left eye developed a macular hole; they
do that sometimes.

Look into a laser?

Not even a laser. One looks into a lens and sees some blue rectangles
for a few seconds. LEDs, not lasers.



The good news is that it can be mostly fixed. The guy who did it is a
genius with a very steady hand.

The tomography is amazing. Just a few seconds looking at some blue
lights.

Yes, looks almost better now than the right eye!

It does. The right eye is normal, a little puckered around the macula.
The treatment is for the doc to peel away the top two layers of cells
in a big patch of the retina, which relieves stress and lets the hole
close. Done by hand. With tweezers. It was interesting, a half hour of
wild light show.


What exactly does the blue light do?

Don\'t know. I should look it up, \"Optical coherence tomography of
macular holes.\" The original resolution is much better than what I
posted, which was scanned from a paper report.

Amazing.

Here\'s a really good tomograph.

https://retinaassociatesofgreaterphiladelphia.com/wp-content/uploads/2021/07/STAGE-3-MAC-HOLE-WITH-PSEUDO-OPERCULUM-CROPPED-WITH-
RA.jpg

You can see the vitreus humor pulled back from the retina, and a bit
that it tore away.

https://en.wikipedia.org/wiki/Optical_coherence_tomography

Thank you very much for the links
Always learning!
Very impressive that wikipedia link!

It\'s interesting to think of making a split-beam interferometer with
wideband light. You get good interference over a very short range of
distances, as opposed to periodic interferance over a wide range with
long-coherence light.

I did see a red line sweep top to bottom when they did the scan.


I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution, but an
incoherent red LED is a lot cheaper.

I knew a guy who patented an HF navigation system sort of like Loran,
but the transmitters sent pseudo-random modulated RF, the idea being
that a cross-correlating receiver could distinguish the ground wave
and ignore ionosphere paths. Same idea, really.

Sadly, he invented that just as GPS was ramping up.

Looks like he re-invented GPS, only at frequencies that do not
work well for BW reasons.

Gerhard

 

[Clifford Heath]

On 5/11/22 11:31, Gerhard Hoffmann wrote:

Am 05.11.22 um 01:04 schrieb John Larkin:
On Mon, 31 Oct 2022 12:29:35 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Mon, 31 Oct 2022 12:21:16 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Sun, 30 Oct 2022 06:18:57 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Sat, 29 Oct 2022 11:47:39 -0700) it happened John
Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
r7sqlhpppp3n8fhhs5nn9hf16tqddb4vcg@4ax.com>:

On Sat, 29 Oct 2022 17:25:34 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

On a sunny day (Sat, 29 Oct 2022 07:34:47 -0700) it happened John
Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
qrdqlhpor5v5h642dr8ida0lqjodp3gdfk@4ax.com>:

On Sat, 29 Oct 2022 04:59:56 GMT, Jan Panteltje
pNaonStpealmtje@yahoo.com> wrote:

https://www.sciencedaily.com/releases/2022/10/221027123919.htm
https://www.rockefeller.edu/news/33135-fruit-flies-move-their-retinas-much-like-humans-move-their-eyes/


Makes me wonder if we will get vibrating camera sensors, maybe
using piezos to
move the CCD ?

Speaking of retinas...

https://www.dropbox.com/s/z4kym11g2qvlgei/Retina_Repair_2022.jpg?raw=1


We don\'t know exactly why the left eye developed a macular hole;
they
do that sometimes.

Look into a laser?

Not even a laser. One looks into a lens and sees some blue rectangles
for a few seconds. LEDs, not lasers.



The good news is that it can be mostly fixed. The guy who did it
is a
genius with a very steady hand.

The tomography is amazing. Just a few seconds looking at some blue
lights.

Yes, looks almost better now than the right eye!

It does. The right eye is normal, a little puckered around the
macula.
The treatment is for the doc to peel away the top two layers of cells
in a big patch of the retina, which relieves stress and lets the hole
close. Done by hand. With tweezers. It was interesting, a half
hour of
wild light show.


What exactly does the blue light do?

Don\'t know. I should look it up, \"Optical coherence tomography of
macular holes.\" The original resolution is much better than what I
posted, which was scanned from a paper report.

Amazing.

Here\'s a really good tomograph.

https://retinaassociatesofgreaterphiladelphia.com/wp-content/uploads/2021/07/STAGE-3-MAC-HOLE-WITH-PSEUDO-OPERCULUM-CROPPED-WITH-

RA.jpg

You can see the vitreus humor pulled back from the retina, and a bit
that it tore away.

https://en.wikipedia.org/wiki/Optical_coherence_tomography

Thank you very much for the links
Always learning!
Very impressive that wikipedia link!

It\'s interesting to think of making a split-beam interferometer with
wideband light. You get good interference over a very short range of
distances, as opposed to periodic interferance over a wide range with
long-coherence light.

I did see a red line sweep top to bottom when they did the scan.


I guess that a femtosecond monochromatic pulse would have the same
effect, wideband optical spectrum and good distance resolution, but an
incoherent red LED is a lot cheaper.

I knew a guy who patented an HF navigation system sort of like Loran,
but the transmitters sent pseudo-random modulated RF, the idea being
that a cross-correlating receiver could distinguish the ground wave
and ignore ionosphere paths. Same idea, really.

Sadly, he invented that just as GPS was ramping up.

Looks like he re-invented GPS, only at frequencies that do not
work well for BW reasons.

The ranging modulation on the Apollo program operated below 1Mbaud, yet
was still capable of ranging accuracy getting down to 1 metre - which
meant they could achieve phase locking within 2-3 degrees after
correlation. So it\'s not clear to me that HF is out of the question for
accurate positioning.

Clifford Heath.

 

[Gerhard Hoffmann]

Am 05.11.22 um 02:12 schrieb Clifford Heath:

On 5/11/22 11:31, Gerhard Hoffmann wrote:
Am 05.11.22 um 01:04 schrieb John Larkin:
On Mon, 31 Oct 2022 12:29:35 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Mon, 31 Oct 2022 12:21:16 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:


I knew a guy who patented an HF navigation system sort of like Loran,
but the transmitters sent pseudo-random modulated RF, the idea being
that a cross-correlating receiver could distinguish the ground wave
and ignore ionosphere paths. Same idea, really.

Sadly, he invented that just as GPS was ramping up.

Looks like he re-invented GPS, only at frequencies that do not
work well for BW reasons.

The ranging modulation on the Apollo program operated below 1Mbaud, yet
was still capable of ranging accuracy getting down to 1 metre - which
meant they could achieve phase locking within 2-3 degrees after
correlation. So it\'s not clear to me that HF is out of the question for
accurate positioning.

1 MBaud means \"enough bandwidth for 1 MB BPSK\". You won\'t get
that BW on HF, much less a clean channel with flat behavior.

BTDT. I have done PN generation, modulation, demodulation,
ranging by cross correlation + sweeping for some TV and phone sats.

Gerhard