ot optics question for Phil...

[John Larkin]

What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?



--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

 

[a a]

On Friday, 12 August 2022 at 01:38:57 UTC+2, John Larkin wrote:

What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?



--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"
Optical Diopter Strength Explained

https://focusers.com/pages/explanation-of-diopter-strength

 

[John Larkin]

On Thu, 11 Aug 2022 17:32:40 -0700 (PDT), a a <manta103g@gmail.com>
wrote:

On Friday, 12 August 2022 at 01:38:57 UTC+2, John Larkin wrote:
What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?



--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"
Optical Diopter Strength Explained

https://focusers.com/pages/explanation-of-diopter-strength

Thanks, but that doesn\'t answer my question.

--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

 

[a a]

On Friday, 12 August 2022 at 02:46:38 UTC+2, John Larkin wrote:

On Thu, 11 Aug 2022 17:32:40 -0700 (PDT), a a <mant...@gmail.com
wrote:
On Friday, 12 August 2022 at 01:38:57 UTC+2, John Larkin wrote:
What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?



--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"
Optical Diopter Strength Explained

https://focusers.com/pages/explanation-of-diopter-strength
Thanks, but that doesn\'t answer my question.
--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

https://wiki.endmyopia.org/wiki/Diopters

 

[John Larkin]

On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

 

[Cydrome Leader]

John Larkin <jjlarkin@highlandtechnology.com> wrote:

On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Next question is where the hell did you get those glasses in the first
place, if you have no idea of what their prescription even is?

 

[John Larkin]

On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

That conversion is not difficult.

Next question is where the hell did you get those glasses in the first
place, if you have no idea of what their prescription even is?

I don\'t have the prescription handy. And I like to measure things.

I think my eye has changed since I got the glasses.

Are you always so rude?



--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

 

[Joe Gwinn]

On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.

This well predates NASA, having been developed by Isaac Newton in the
16th century:

..<https://en.wikipedia.org/wiki/Opticks>


Diopters are the inverse of the focal length in meters. Yes, a lens
can have negative power expressed in diopters:

..<https://en.wikipedia.org/wiki/Thin_lens>


Joe Gwinn

 

[Phil Hobbs]

John Larkin wrote:

On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'ll get a better measurement by making the aperture much smaller than
the focal length. (The magnitude of the FL, that is.)

An object at a distance d_o from the center of a thin lens of focal
length f produces an image at a distance d_i, where

1/d_o + 1/d_i = 1/f.

The sun is very distant, so we can ignore 1/d_0, so that the image of
the sun is at f, which for a concave lens is on the side towards the sun.

You figure the FL using similar triangles as usual, except
backwards--given two projections, find the focal point. That takes one
more line of algebra.

The sun \'s angular subtense is about 0.5 degrees, so you have to take
that contribution out somehow--if you measure the disk diameter out to
where the intensity falls to nearly zero, your measured angle will be
0.5 degrees too large, and your measured FL correspondingly too short.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Cydrome Leader]

Joe Gwinn <joegwinn@comcast.net> wrote:

On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.

It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

I have no issue with inch focal lengths by themselves. Tons of \"standard\"
sizes in mm for objective lenses are based off the original ones in
inches.

 

[Phil Hobbs]

Cydrome Leader wrote:

Joe Gwinn <joegwinn@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.

It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

I have no issue with inch focal lengths by themselves. Tons of \"standard\"
sizes in mm for objective lenses are based off the original ones in
inches.

Eyeglasses prescriptions are in dioptres.

Don\'t worry, CD, JL is very unlikely to crash into Mars this week.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Larkin]

On Fri, 12 Aug 2022 18:24:25 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

Joe Gwinn <joegwinn@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.

It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

I have no issue with inch focal lengths by themselves. Tons of \"standard\"
sizes in mm for objective lenses are based off the original ones in
inches.

Glasses are prescribed in diopters. I measured the focal length of
that lens as -11 inches. That\'s about -3.5 diopters.

Is that weird?

--

John Larkin Highland Technology, Inc trk

The cork popped merrily, and Lord Peter rose to his feet.
\"Bunter\", he said, \"I give you a toast. The triumph of Instinct over Reason\"

 

[Cydrome Leader]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Cydrome Leader wrote:
Joe Gwinn <joegwinn@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.

It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

I have no issue with inch focal lengths by themselves. Tons of \"standard\"
sizes in mm for objective lenses are based off the original ones in
inches.



Eyeglasses prescriptions are in dioptres.

He doesn\'t know his rx, or that of the glasses. It\'s all pointless.

> Don\'t worry, CD, JL is very unlikely to crash into Mars this week.

Ha.

 

[Phil Hobbs]

Cydrome Leader wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Cydrome Leader wrote:
Joe Gwinn <joegwinn@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.

It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

I have no issue with inch focal lengths by themselves. Tons of \"standard\"
sizes in mm for objective lenses are based off the original ones in
inches.



Eyeglasses prescriptions are in dioptres.

He doesn\'t know his rx, or that of the glasses. It\'s all pointless.

If the resting focus of that eye is +2.3 dioptre (17 inch FL), then a
-3.6 dioptre corrective is indeed too strong. (This is after cataract
surgery, so there\'s no accommodation to take into account.)

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Walliker]

On Friday, 12 August 2022 at 19:24:32 UTC+1, Cydrome Leader wrote:

Joe Gwinn <joeg...@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
pres...@MUNGEpanix.com> wrote:

John Larkin <jjla...@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjla...@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.
It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

Well, the diopter is just the reciprocal of the focal length in metres, so
it is relevant. Opticians use diopters because lenses can be stacked
in front of each other and the powers in diopters simply add or subtract
as appropriate. This is much easier than working directly with focal lengths.

I have no issue with inch focal lengths by themselves. Tons of \"standard\"
sizes in mm for objective lenses are based off the original ones in
inches.

John

 

[server]

On Sun, 14 Aug 2022 15:12:04 -0700 (PDT), John Walliker
<jrwalliker@gmail.com> wrote:

On Friday, 12 August 2022 at 19:24:32 UTC+1, Cydrome Leader wrote:
Joe Gwinn <joeg...@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
pres...@MUNGEpanix.com> wrote:

John Larkin <jjla...@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjla...@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.
It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

Well, the diopter is just the reciprocal of the focal length in metres, so
it is relevant. Opticians use diopters because lenses can be stacked
in front of each other and the powers in diopters simply add or subtract
as appropriate. This is much easier than working directly with focal lengths.

It\'s just like resistors in parallel.

 

[Cydrome Leader]

jlarkin@highlandsniptechnology.com wrote:

On Sun, 14 Aug 2022 15:12:04 -0700 (PDT), John Walliker
jrwalliker@gmail.com> wrote:

On Friday, 12 August 2022 at 19:24:32 UTC+1, Cydrome Leader wrote:
Joe Gwinn <joeg...@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
pres...@MUNGEpanix.com> wrote:

John Larkin <jjla...@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjla...@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.
It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

Well, the diopter is just the reciprocal of the focal length in metres, so
it is relevant. Opticians use diopters because lenses can be stacked
in front of each other and the powers in diopters simply add or subtract
as appropriate. This is much easier than working directly with focal lengths.

It\'s just like resistors in parallel.

When is the last time you use mhos in a calcuation?

 

[server]

On Mon, 15 Aug 2022 18:26:44 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sun, 14 Aug 2022 15:12:04 -0700 (PDT), John Walliker
jrwalliker@gmail.com> wrote:

On Friday, 12 August 2022 at 19:24:32 UTC+1, Cydrome Leader wrote:
Joe Gwinn <joeg...@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
pres...@MUNGEpanix.com> wrote:

John Larkin <jjla...@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjla...@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.
It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

Well, the diopter is just the reciprocal of the focal length in metres, so
it is relevant. Opticians use diopters because lenses can be stacked
in front of each other and the powers in diopters simply add or subtract
as appropriate. This is much easier than working directly with focal lengths.

It\'s just like resistors in parallel.

When is the last time you use mhos in a calcuation?

I type

rval
1/x

(RPN) often. I don\'t call them mhos; they are actually Siemens.


What resistor do you put across 5 ohms to get 3 ohms?

3
1/x
5
1/x
-
1/x

 

[Cydrome Leader]

jlarkin@highlandsniptechnology.com wrote:

On Mon, 15 Aug 2022 18:26:44 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sun, 14 Aug 2022 15:12:04 -0700 (PDT), John Walliker
jrwalliker@gmail.com> wrote:

On Friday, 12 August 2022 at 19:24:32 UTC+1, Cydrome Leader wrote:
Joe Gwinn <joeg...@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
pres...@MUNGEpanix.com> wrote:

John Larkin <jjla...@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjla...@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.
It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

Well, the diopter is just the reciprocal of the focal length in metres, so
it is relevant. Opticians use diopters because lenses can be stacked
in front of each other and the powers in diopters simply add or subtract
as appropriate. This is much easier than working directly with focal lengths.

It\'s just like resistors in parallel.

When is the last time you use mhos in a calcuation?

I type

rval
1/x

(RPN) often. I don\'t call them mhos; they are actually Siemens.


What resistor do you put across 5 ohms to get 3 ohms?

3
1/x
5
1/x
-
1/x

Seems like the answer is never. I see lots of repetetive 1 over
calculations.

There really is no going back once you learn RPN. Even a fancy calculator
where you can see rows of nested braces just doesn\'t compare.

I always though mhos were just odd. So when did you last use susceptance,
in siemens of course? Maybe it\'s time to hawk special \"ultra high
susceptance\" cables to the audiophiles.

 

[Jeroen Belleman]

On 2022-08-16 23:06, Cydrome Leader wrote:

jlarkin@highlandsniptechnology.com wrote:
On Mon, 15 Aug 2022 18:26:44 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sun, 14 Aug 2022 15:12:04 -0700 (PDT), John Walliker
jrwalliker@gmail.com> wrote:

On Friday, 12 August 2022 at 19:24:32 UTC+1, Cydrome Leader wrote:
Joe Gwinn <joeg...@comcast.net> wrote:
On Fri, 12 Aug 2022 04:40:54 -0000 (UTC), Cydrome Leader
pres...@MUNGEpanix.com> wrote:

John Larkin <jjla...@highlandtechnology.com> wrote:
On Thu, 11 Aug 2022 16:38:38 -0700, John Larkin
jjla...@highlandtechnology.com> wrote:


What\'s a good way to measure the negative diopter of my glasses, given
minimal tools up the the cabin?

I can let the sun shine through a lens and see an enlarged circle on
the ground a few feet away. What\'s the math on that?

I found it online.

https://physics.stackexchange.com/questions/566207/how-to-measure-the-strength-of-a-prescription-eyeglass-lens

My lens is 2\" wide and sunlight projects a 4\" wide image at 11\" from a
screen. So the fl of the lens is -11\".

That\'s bad, since that eye focuses at about 17\". These glasses are
over-correcting.

You\'re pulling some weird NASA moves by asking \"what\'s the diopter of a
lense\" and then concluding a focal length of -11 inches.

Nothing weird here. Just some simple optics.
It is weird. He\'s going on about diopters, but they\'re not a part of
either known or unknowns in what he\'s trying to calculate or confirm.

Well, the diopter is just the reciprocal of the focal length in metres, so
it is relevant. Opticians use diopters because lenses can be stacked
in front of each other and the powers in diopters simply add or subtract
as appropriate. This is much easier than working directly with focal lengths.

It\'s just like resistors in parallel.

When is the last time you use mhos in a calcuation?

I type

rval
1/x

(RPN) often. I don\'t call them mhos; they are actually Siemens.


What resistor do you put across 5 ohms to get 3 ohms?

3
1/x
5
1/x
-
1/x


Seems like the answer is never. I see lots of repetetive 1 over
calculations.

There really is no going back once you learn RPN. Even a fancy calculator
where you can see rows of nested braces just doesn\'t compare.

I always though mhos were just odd. So when did you last use susceptance,
in siemens of course? Maybe it\'s time to hawk special \"ultra high
susceptance\" cables to the audiophiles.

Conductance, susceptance, admittance, they have their uses. In the
design of matching networks, filters and pulse forming networks, it\'s
common to switch back and forth between those and their reciprocals
all the time.

Jeroen Belleman