Diffraction Limiting a Mk I Eyeball

I was doing a Christmas lecture earlier in the the week on "Light and
Colour". I had an unexpectedly strong positive audience reaction from a
very simple and cheap demonstration using 0.1-0.2mm diameter pinholes
in aluminium foil held to the eye. Materials are so cheap and prep so
easy that everyone can see this with their own eyes. And it is far more
convincing to them than any number of fancy laser based demos!

This is roughly equivalent to having a pupil stopped down to 1/10 or
1/20th of the normal 2mm daylight size and is small enough to give a
very clear stable Airy disk on point sources like Christmas tree lights
whilst still retaining colour vision. The bullseye appearance of point
sources came as a big surprise to those without a science background.
Edges are obviously soft and bright areas surrounded by a darker halo.

The main light source was a desktop quartz halogen with foil hung over
the front and a 2mm hole in line with the bulb filament. This gave very
pleasing views of the diffraction pattern of the pinhole. But it was the
coloured Christmas lights that people found most striking.

And by swapping pinholes (which were of somewhat variable size) with
their neighbours the audience quickly realised for themselves that the
smallest pinholes had the biggest and faintest diffraction patterns.

It also increases depth of field allowing very fine print to be read
with relative ease when held suitably close to the eye. I discovered in
the process that a few young children in the audience with otherwise
normal vision could read 2pt text with the unaided eye!

I hope this is of use to others in showing convincing diffraction
effects to a lay audience using minimal cheap hardware.

NB the real Royal Institution Christmas science lectures are titled
"Size Matters" and are being televised on BBC4 at 8pm this week.

Regards,
Martin Brown

Martin Brown wrote in message
...
I was doing a Christmas lecture earlier in the the week on "Light and
Colour". I had an unexpectedly strong positive audience reaction from a
very simple and cheap demonstration using 0.1-0.2mm diameter pinholes
in aluminium foil held to the eye. Materials are so cheap and prep so
easy that everyone can see this with their own eyes. And it is far more
convincing to them than any number of fancy laser based demos!

This is roughly equivalent to having a pupil stopped down to 1/10 or
1/20th of the normal 2mm daylight size and is small enough to give a
very clear stable Airy disk on point sources like Christmas tree lights
whilst still retaining colour vision. The bullseye appearance of point
sources came as a big surprise to those without a science background.
Edges are obviously soft and bright areas surrounded by a darker halo.

The main light source was a desktop quartz halogen with foil hung over
the front and a 2mm hole in line with the bulb filament. This gave very
pleasing views of the diffraction pattern of the pinhole. But it was the
coloured Christmas lights that people found most striking.

And by swapping pinholes (which were of somewhat variable size) with
their neighbours the audience quickly realised for themselves that the
smallest pinholes had the biggest and faintest diffraction patterns.

It also increases depth of field allowing very fine print to be read
with relative ease when held suitably close to the eye. I discovered in
the process that a few young children in the audience with otherwise
normal vision could read 2pt text with the unaided eye!

I hope this is of use to others in showing convincing diffraction
effects to a lay audience using minimal cheap hardware.

NB the real Royal Institution Christmas science lectures are titled
"Size Matters" and are being televised on BBC4 at 8pm this week.

Regards,
Martin Brown


An umbrella and nightime streetlamp is inexpensive for diffraction pattern.

I've taken over running the Southampton part of the "Science Cafe" lecture
structure if anyone in central Southern England could give some sort of
science talk in
2011
http://www.divdev.fsnet.co.uk/scicaf.htm
national structure
http://www.cafescientifique.org

"N_Cook" wrote in message
...
| Martin Brown wrote in message
| ...
| I was doing a Christmas lecture earlier in the the week on "Light and
| Colour". I had an unexpectedly strong positive audience reaction from a
| very simple and cheap demonstration using 0.1-0.2mm diameter pinholes
| in aluminium foil held to the eye. Materials are so cheap and prep so
| easy that everyone can see this with their own eyes. And it is far more
| convincing to them than any number of fancy laser based demos!
|
| This is roughly equivalent to having a pupil stopped down to 1/10 or
| 1/20th of the normal 2mm daylight size and is small enough to give a
| very clear stable Airy disk on point sources like Christmas tree lights
| whilst still retaining colour vision. The bullseye appearance of point
| sources came as a big surprise to those without a science background.
| Edges are obviously soft and bright areas surrounded by a darker halo.
|
| The main light source was a desktop quartz halogen with foil hung over
| the front and a 2mm hole in line with the bulb filament. This gave very
| pleasing views of the diffraction pattern of the pinhole. But it was the
| coloured Christmas lights that people found most striking.
|
| And by swapping pinholes (which were of somewhat variable size) with
| their neighbours the audience quickly realised for themselves that the
| smallest pinholes had the biggest and faintest diffraction patterns.
|
| It also increases depth of field allowing very fine print to be read
| with relative ease when held suitably close to the eye. I discovered in
| the process that a few young children in the audience with otherwise
| normal vision could read 2pt text with the unaided eye!
|
| I hope this is of use to others in showing convincing diffraction
| effects to a lay audience using minimal cheap hardware.
|
| NB the real Royal Institution Christmas science lectures are titled
| "Size Matters" and are being televised on BBC4 at 8pm this week.
|
| Regards,
| Martin Brown
|
|
| An umbrella and nightime streetlamp is inexpensive for diffraction
pattern.
|
Take an ordinary CD or DVD and hold it horizontally, the rim touching
your cheek just below your eye. Now look at a street light, in the CD.

I took this image of a fluorescent lamp using a web cam.
http://www.androcles01.pwp.blueyonde...pDVDWebCam.JPG


| I've taken over running the Southampton part of the "Science Cafe" lecture
| structure if anyone in central Southern England could give some sort of
| science talk in
| 2011
| http://www.divdev.fsnet.co.uk/scicaf.htm
| national structure
| http://www.cafescientifique.org
|
|
|
|
|

On Dec 31, 3:00*pm, Androgones scribbled:

| I've taken over running the Southampton part of the "Science Cafe" lecture
| structure if anyone in central Southern England could give some sort of
| science talk in
| 2011
|http://www.divdev.fsnet.co.uk/scicaf.htm

Please, Sir?
Can I come along and swear just like you?
Can I come along and blaspheme about The Baby Prophet Einstein?
Can I come along and urinate all over your Relativity?
Can I come along and spank you publicly for being naughty on Abusenet?
Thank you kindly, Sir, and no mistake.
God bless you, Sir. May your camel have a thousand humps.
Ahem. We know where you live..! :-)

In sci.astro.amateur message ,
Fri, 31 Dec 2010 13:05:43, N_Cook posted:


An umbrella and nightime streetlamp is inexpensive for diffraction pattern.


Try some equivalent of an old-fashioned metal foil milk-bottle top,
pierced with the smallest closest holes you can do by hand with a fine
sewing needle, then using the foil as a monocle to inspect a distant LP
sodium lamp. The effect is not as pretty as from a CD, but it's
definitely there. The millimetre scale of a plastic ruler, at grazing
incidence, will also show an effect.

--
(c) John Stockton, near London.
Web http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, and links.
Correct = 4-line sig. separator as above, a line precisely "-- " (RFC5536/7)
Do not Mail News to me. Before a reply, quote with "" or " " (RFC5536/7)

On 31/12/2010 13:05, N_Cook wrote:
Martin wrote in message
...
I was doing a Christmas lecture earlier in the the week on "Light and
Colour". I had an unexpectedly strong positive audience reaction from a
very simple and cheap demonstration using 0.1-0.2mm diameter pinholes
in aluminium foil held to the eye. Materials are so cheap and prep so
easy that everyone can see this with their own eyes. And it is far more
convincing to them than any number of fancy laser based demos!

This is roughly equivalent to having a pupil stopped down to 1/10 or
1/20th of the normal 2mm daylight size and is small enough to give a
very clear stable Airy disk on point sources like Christmas tree lights
whilst still retaining colour vision. The bullseye appearance of point
sources came as a big surprise to those without a science background.
Edges are obviously soft and bright areas surrounded by a darker halo.

The main light source was a desktop quartz halogen with foil hung over
the front and a 2mm hole in line with the bulb filament. This gave very
pleasing views of the diffraction pattern of the pinhole. But it was the
coloured Christmas lights that people found most striking.

And by swapping pinholes (which were of somewhat variable size) with
their neighbours the audience quickly realised for themselves that the
smallest pinholes had the biggest and faintest diffraction patterns.

It also increases depth of field allowing very fine print to be read
with relative ease when held suitably close to the eye. I discovered in
the process that a few young children in the audience with otherwise
normal vision could read 2pt text with the unaided eye!

I hope this is of use to others in showing convincing diffraction
effects to a lay audience using minimal cheap hardware.


An umbrella and nightime streetlamp is inexpensive for diffraction pattern.

This pinhole trick was used as a last minute simple diffraction demo
after my tame street lamp using an 18W SOX (low pressure sodium lamp)
refused to strike a proper yellow arc. I suspect the outer vacuum has
leaked and it isn't getting warm enough now to vapourise the sodium.

The pinhole hardware is so simple and its effect on point sources very
striking. It was clear most people have never seen a diffraction limited
image and found it fascinating to see with just their own eyes. Most of
the other demos were projected onto a screen.

Shovelware CDs at glancing incidence are another easy win.

Clouded out for the eclipse this morning in N Yorks.

Regards,
Martin Brown

On Dec 30 2010, 8:06*am, Martin Brown |||
wrote:
I was doing a Christmas lecture earlier in the the week on "Light and
Colour". I had an unexpectedly strong positive audience reaction from a
very simple and cheap demonstration using *0.1-0.2mm diameter pinholes
in aluminium foil held to the eye. Materials are so cheap and prep so
easy that everyone can see this with their own eyes. And it is far more
convincing to them than any number of fancy laser based demos!

This is roughly equivalent to having a pupil stopped down to *1/10 or
1/20th of the normal 2mm daylight size and is small enough to give a
very clear stable Airy disk on point sources like Christmas tree lights
whilst still retaining colour vision. The bullseye appearance of point
sources came as a big surprise to those without a science background.
Edges are obviously soft and bright areas surrounded by a darker halo.

The main light source was a desktop quartz halogen with foil hung over
the front and a 2mm hole in line with the bulb filament. This gave very
pleasing views of the diffraction pattern of the pinhole. But it was the
coloured Christmas lights that people found most striking.

And by swapping pinholes (which were of somewhat variable size) with
their neighbours the audience quickly realised for themselves that the
smallest pinholes had the biggest and faintest diffraction patterns.

It also increases depth of field allowing very fine print to be read
with relative ease when held suitably close to the eye. I discovered in
the process that a few young children in the audience with otherwise
normal vision could read 2pt text with the unaided eye!

I hope this is of use to others in showing convincing diffraction
effects to a lay audience using minimal cheap hardware.

NB the real Royal Institution Christmas science lectures are titled
"Size Matters" and are being televised on BBC4 at 8pm this week.

Regards,
Martin Brown

You can also easily demonstrate the effect of aperture on MTF
(modulation transfer function). Look at cubism type pictures or
pixelated pictures on TV (used to hide identity).

Using one eye, squint at the object. This reduces the aperture,
cutting out the high frequencies and removing the sharp boundaries.
The "original" picture can be seen quite clearly.

www.richardfisher.com

On Jan 4, 2:07*pm, Helpful person wrote:
On Dec 30 2010, 8:06*am, Martin Brown |||





wrote:
I was doing a Christmas lecture earlier in the the week on "Light and
Colour". I had an unexpectedly strong positive audience reaction from a
very simple and cheap demonstration using *0.1-0.2mm diameter pinholes
in aluminium foil held to the eye. Materials are so cheap and prep so
easy that everyone can see this with their own eyes. And it is far more
convincing to them than any number of fancy laser based demos!

This is roughly equivalent to having a pupil stopped down to *1/10 or
1/20th of the normal 2mm daylight size and is small enough to give a
very clear stable Airy disk on point sources like Christmas tree lights
whilst still retaining colour vision. The bullseye appearance of point
sources came as a big surprise to those without a science background.
Edges are obviously soft and bright areas surrounded by a darker halo.

The main light source was a desktop quartz halogen with foil hung over
the front and a 2mm hole in line with the bulb filament. This gave very
pleasing views of the diffraction pattern of the pinhole. But it was the
coloured Christmas lights that people found most striking.

And by swapping pinholes (which were of somewhat variable size) with
their neighbours the audience quickly realised for themselves that the
smallest pinholes had the biggest and faintest diffraction patterns.

It also increases depth of field allowing very fine print to be read
with relative ease when held suitably close to the eye. I discovered in
the process that a few young children in the audience with otherwise
normal vision could read 2pt text with the unaided eye!

I hope this is of use to others in showing convincing diffraction
effects to a lay audience using minimal cheap hardware.

NB the real Royal Institution Christmas science lectures are titled
"Size Matters" and are being televised on BBC4 at 8pm this week.

Regards,
Martin Brown

You can also easily demonstrate the effect of aperture on MTF
(modulation transfer function). *Look at cubism type pictures or
pixelated pictures on TV (used to hide identity).

Using one eye, squint at the object. *This reduces the aperture,
cutting out the high frequencies and removing the sharp boundaries.
The "original" picture can be seen quite clearly.

www.richardfisher.com

http://www.opticalillusion.net/optic...xelated-faces/

Helpful person wrote in message
...
On Dec 30 2010, 8:06 am, Martin Brown |||
wrote:
I was doing a Christmas lecture earlier in the the week on "Light and
Colour". I had an unexpectedly strong positive audience reaction from a
very simple and cheap demonstration using 0.1-0.2mm diameter pinholes
in aluminium foil held to the eye. Materials are so cheap and prep so
easy that everyone can see this with their own eyes. And it is far more
convincing to them than any number of fancy laser based demos!

This is roughly equivalent to having a pupil stopped down to 1/10 or
1/20th of the normal 2mm daylight size and is small enough to give a
very clear stable Airy disk on point sources like Christmas tree lights
whilst still retaining colour vision. The bullseye appearance of point
sources came as a big surprise to those without a science background.
Edges are obviously soft and bright areas surrounded by a darker halo.

The main light source was a desktop quartz halogen with foil hung over
the front and a 2mm hole in line with the bulb filament. This gave very
pleasing views of the diffraction pattern of the pinhole. But it was the
coloured Christmas lights that people found most striking.

And by swapping pinholes (which were of somewhat variable size) with
their neighbours the audience quickly realised for themselves that the
smallest pinholes had the biggest and faintest diffraction patterns.

It also increases depth of field allowing very fine print to be read
with relative ease when held suitably close to the eye. I discovered in
the process that a few young children in the audience with otherwise
normal vision could read 2pt text with the unaided eye!

I hope this is of use to others in showing convincing diffraction
effects to a lay audience using minimal cheap hardware.

NB the real Royal Institution Christmas science lectures are titled
"Size Matters" and are being televised on BBC4 at 8pm this week.

Regards,
Martin Brown

You can also easily demonstrate the effect of aperture on MTF
(modulation transfer function). Look at cubism type pictures or
pixelated pictures on TV (used to hide identity).

Using one eye, squint at the object. This reduces the aperture,
cutting out the high frequencies and removing the sharp boundaries.
The "original" picture can be seen quite clearly.

www.richardfisher.com


&&&&&&&

But on the other hand if the light level is high enough and you've forgotten
your reading glases - you can read small print by "stopping down" an eye by
viewing through the central hole between bent-over thumb and first skin fold
of the index finger of a partial fist-making. Limiting to the central least
distorted part of the eyeball

On Jan 6, 3:23*am, "N_Cook" wrote:
Helpful person wrote in message

...
On Dec 30 2010, 8:06 am, Martin Brown |||



wrote:
I was doing a Christmas lecture earlier in the the week on "Light and
Colour". I had an unexpectedly strong positive audience reaction from a
very simple and cheap demonstration using 0.1-0.2mm diameter pinholes
in aluminium foil held to the eye. Materials are so cheap and prep so
easy that everyone can see this with their own eyes. And it is far more
convincing to them than any number of fancy laser based demos!

This is roughly equivalent to having a pupil stopped down to 1/10 or
1/20th of the normal 2mm daylight size and is small enough to give a
very clear stable Airy disk on point sources like Christmas tree lights
whilst still retaining colour vision. The bullseye appearance of point
sources came as a big surprise to those without a science background.
Edges are obviously soft and bright areas surrounded by a darker halo.

The main light source was a desktop quartz halogen with foil hung over
the front and a 2mm hole in line with the bulb filament. This gave very
pleasing views of the diffraction pattern of the pinhole. But it was the
coloured Christmas lights that people found most striking.

And by swapping pinholes (which were of somewhat variable size) with
their neighbours the audience quickly realised for themselves that the
smallest pinholes had the biggest and faintest diffraction patterns.

It also increases depth of field allowing very fine print to be read
with relative ease when held suitably close to the eye. I discovered in
the process that a few young children in the audience with otherwise
normal vision could read 2pt text with the unaided eye!

I hope this is of use to others in showing convincing diffraction
effects to a lay audience using minimal cheap hardware.

NB the real Royal Institution Christmas science lectures are titled
"Size Matters" and are being televised on BBC4 at 8pm this week.

Regards,
Martin Brown

You can also easily demonstrate the effect of aperture on MTF
(modulation transfer function). *Look at cubism type pictures or
pixelated pictures on TV (used to hide identity).

Using one eye, squint at the object. *This reduces the aperture,
cutting out the high frequencies and removing the sharp boundaries.
The "original" picture can be seen quite clearly.

www.richardfisher.com

&&&&&&&

But on the other hand if the light level is high enough and you've forgotten
your reading glases - you can read small print by "stopping down" an eye by
viewing through the central hole between bent-over thumb and first skin fold
of the index finger of a partial fist-making. Limiting to the central least
distorted part of the eyeball

It's not a matter of "less distorted" or aberrations it's a matter of
spatial filtering.

www.richardfisher.com