From Newsgroup: sci.electronics.design

https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

Maybe two can be stacked for double the magnification.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

john larkin <jl@glen--canyon.com>wrote: >>https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

Maybe two can be stacked for double the magnification.

I have a cheap fire starter, a big magnifying glass, and a small loupe
There was a survival program on TV where a guy used a piece of ice in the right form as lens
to make a fire.

Rubbing 2 pieces of wood works too.

I have some sheet from ebay too, 2015, experimented with it in 2015
Full Page Magnifying Sheet Fresnel Lens 3X, like this (different seller I used):
https://www.ebay.com/itm/365848975882

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From Newsgroup: sci.electronics.design

Jan Panteltje <alien@comet.invalid> wrote:

john larkin <jl@glen--canyon.com>wrote: >>https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

Maybe two can be stacked for double the magnification.

I have a cheap fire starter, a big magnifying glass, and a small loupe
There was a survival program on TV where a guy used a piece of ice in the right form as lens to make a fire.

Doesn't water absorb infra-red?
--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 01/01/2026 00:53, john larkin wrote:

https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

They can work up to a point and are very handy by being flat.
Keep it in a soft envelope to protect from scratches.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

I think that is a bit optimistic for a credit card sized one.
I prefer a high energy ferrocerium spark - more use in the UK

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

The hard part is finding kindling that is dry enough to take.

Maybe two can be stacked for double the magnification.

You may find the moire patterns as the two sets of concentric circles
interact rather distracting. If you can hold them apart by the right
amount ~0.7f you can make a sort of Ramsden eyepiece:

https://en.wikipedia.org/wiki/Eyepiece#Ramsden

Nothing beats a good loupe for close inspection.
Although a pair of strong reading glasses on top of your prescription
glasses can be very handy as a quick way to see finer detail.
(old watchmakers trick)
--
Martin Brown

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On Thu, 1 Jan 2026 11:04:22 +0000, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:

On 01/01/2026 00:53, john larkin wrote:

https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

They can work up to a point and are very handy by being flat.
Keep it in a soft envelope to protect from scratches.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

I think that is a bit optimistic for a credit card sized one.
I prefer a high energy ferrocerium spark - more use in the UK

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

The hard part is finding kindling that is dry enough to take.

Maybe two can be stacked for double the magnification.

You may find the moire patterns as the two sets of concentric circles >interact rather distracting. If you can hold them apart by the right
amount ~0.7f you can make a sort of Ramsden eyepiece:

https://en.wikipedia.org/wiki/Eyepiece#Ramsden

Nothing beats a good loupe for close inspection.
Although a pair of strong reading glasses on top of your prescription >glasses can be very handy as a quick way to see finer detail.
(old watchmakers trick)

I had cataract surgery and decided to be nearsighted, since most of my
life is close-up.

But Mo is getting farsighted and can't read tiny labels at the grocery
store. She sometimes buys whole wheat pizza dough and bread (yuk)
instead of proper white sourdough. I figure that she can keep one of
these in her wallet.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

liz@poppyrecords.invalid.invalid (Liz Tuddenham)wrote:

Jan Panteltje <alien@comet.invalid> wrote:

john larkin <jl@glen--canyon.com>wrote:

https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

Maybe two can be stacked for double the magnification.

I have a cheap fire starter, a big magnifying glass, and a small loupe
There was a survival program on TV where a guy used a piece of ice in the
right form as lens to make a fire.

Doesn't water absorb infra-red?

Yes, but you would need a meter or 2 for full absorbtion
absorbtion of EM radiation in ice is the same
So a few mm lens should be no problem,
but I did not try it myself.

https://www.pbs.org/weta/roughscience/series3/ice/icelens.html

More:
https://pmc.ncbi.nlm.nih.gov/articles/PMC6501920/
https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water

google
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 2026-01-01 01:53, john larkin wrote:

https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

Maybe two can be stacked for double the magnification.

John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

They work fine. SWMBO forgot her lighter and wanted to smoke.
I have such a lens in my purse and lighted the cigarette.

Arie.
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

Arie de Muijnck <noreply@ademu.nl>wrote:

On 2026-01-01 01:53, john larkin wrote:
https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

Maybe two can be stacked for double the magnification.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

They work fine. SWMBO forgot her lighter and wanted to smoke.
I have such a lens in my purse and lighted the cigarette.

Arie.

I could (and many I am sure) just use my glasses.
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

Jan Panteltje <alien@comet.invalid> wrote:

liz@poppyrecords.invalid.invalid (Liz Tuddenham)wrote:

Jan Panteltje <alien@comet.invalid> wrote:

john larkin <jl@glen--canyon.com>wrote:

https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title >> >

One can carry one of these in a wallet and have a decent magnifier
handy.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

Maybe two can be stacked for double the magnification.

I have a cheap fire starter, a big magnifying glass, and a small loupe
There was a survival program on TV where a guy used a piece of ice in the >> right form as lens to make a fire.

Doesn't water absorb infra-red?

Yes, but you would need a meter or 2 for full absorbtion
absorbtion of EM radiation in ice is the same
So a few mm lens should be no problem,

I thought the water heat-absorbers on cinema arc lamps were only an inch
or two thick.
--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 1/1/2026 4:04 AM, Martin Brown wrote:

Nothing beats a good loupe for close inspection.
Although a pair of strong reading glasses on top of your prescription glasses
can be very handy as a quick way to see finer detail.
(old watchmakers trick)

I started carrying a cell phone just as a timepiece (cuz
every time I asked someone "what time is it?" they looked
at their cell phone -- hey, I can do that!).

The *second* application I found for it was as a camera...
so I could snap a photo of some tiny thing and then enlarge
it (zoom) to see the fine detail. This is especially handy
for reading the microprint that is now common on devices (does
that say "12V @ 0.2A" or "15V @ 0.2A"?). The flash/illuminator
makes this particularly useful in low light situations (like
when you are trying to examine a device at the bottom of a
pallet of other devices and don't want to have to unload the
pallet just to gain access to it!)

[You can, of course, also use it as a "variable gain magnifier"
if you can maintain a sight line to it while viewing the
object in question]

I used to keep a jewelers loupe in the console of the car but
that proved too tedious (trek out to the car to fetch it any
time you needed to see something "fine" -- the phone was in
your pocket as a timepiece so much handier!)
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On Thu, 1 Jan 2026 14:10:48 -0700, Don Y <blockedofcourse@foo.invalid>
wrote:

On 1/1/2026 4:04 AM, Martin Brown wrote:

Nothing beats a good loupe for close inspection.
Although a pair of strong reading glasses on top of your prescription glasses
can be very handy as a quick way to see finer detail.
(old watchmakers trick)

I started carrying a cell phone just as a timepiece (cuz
every time I asked someone "what time is it?" they looked
at their cell phone -- hey, I can do that!).

The *second* application I found for it was as a camera...
so I could snap a photo of some tiny thing and then enlarge
it (zoom) to see the fine detail. This is especially handy
for reading the microprint that is now common on devices (does
that say "12V @ 0.2A" or "15V @ 0.2A"?). The flash/illuminator
makes this particularly useful in low light situations (like
when you are trying to examine a device at the bottom of a
pallet of other devices and don't want to have to unload the
pallet just to gain access to it!)

[You can, of course, also use it as a "variable gain magnifier"
if you can maintain a sight line to it while viewing the
object in question]

My Samsung phone makes an excellent magnifier, about 4x.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 01/01/2026 17:34, Liz Tuddenham wrote:

Jan Panteltje <alien@comet.invalid> wrote:

liz@poppyrecords.invalid.invalid (Liz Tuddenham)wrote:

Jan Panteltje <alien@comet.invalid> wrote:

john larkin <jl@glen--canyon.com>wrote:

https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title >>>>>

One can carry one of these in a wallet and have a decent magnifier
handy.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

Maybe two can be stacked for double the magnification.

I have a cheap fire starter, a big magnifying glass, and a small loupe >>>> There was a survival program on TV where a guy used a piece of ice in the >>>> right form as lens to make a fire.

Doesn't water absorb infra-red?

Yes, but you would need a meter or 2 for full absorbtion
absorbtion of EM radiation in ice is the same
So a few mm lens should be no problem,

I thought the water heat-absorbers on cinema arc lamps were only an inch
or two thick.

Ice is much more transparent than water in the near infra-red region.
Both are very transparent in the visible part of the spectrum. Most of
the energy in sunlight is in the visible and near infra-red.
John

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On Thu, 01 Jan 2026 16:23:45 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

Arie de Muijnck <noreply@ademu.nl>wrote:

On 2026-01-01 01:53, john larkin wrote:
https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

Maybe two can be stacked for double the magnification.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

They work fine. SWMBO forgot her lighter and wanted to smoke.
I have such a lens in my purse and lighted the cigarette.

Arie.

I could (and many I am sure) just use my glasses.

Not mine. They are concave.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

In article <tvgblkltgee4erp94d0e3vrreeehf15hak@4ax.com>,
john larkin <jl@glen--canyon.com> wrote: >https://www.amazon.com/dp/B0FS7TQ4CV?ref=ppx_yo2ov_dt_b_fed_asin_title

One can carry one of these in a wallet and have a decent magnifier
handy.

As long as it can create a real image of the sun, it can ignite
e.g. a cotton lint.
Fresnel lenses are no different from glass lenses in this respect.
As a survival tool a Fresnel lens has the advantage that it is
much lighter, especially compared to larger glass lenses.

They claim it can start fires too. I'll test that if the sun ever
comes out again.

FCS, it is a normal lens.
I have one, and it is light!

Maybe two can be stacked for double the magnification.

The main thing is the surface area, that account for the power
collected.
Getting the image of the sun smaller, increases the temperature
but that is not that important.

You realize that a Fresnel is thin,irrespective of focal length?
If you want to make the focus length smaller, you just have to
redesign the lens. No need to stack.

John Larkin

--
The Chinese government is satisfied with its military superiority over USA.
The next 5 year plan has as primary goal to advance life expectancy
over 80 years, like Western Europe.
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 03/01/2026 10:50, albert@spenarnc.xs4all.nl wrote:

In article <tvgblkltgee4erp94d0e3vrreeehf15hak@4ax.com>,
john larkin <jl@glen--canyon.com> wrote:

Maybe two can be stacked for double the magnification.

The main thing is the surface area, that account for the power
collected.
Getting the image of the sun smaller, increases the temperature
but that is not that important.

Having dark absorber material makes a big difference. White cotton wool
is much harder to ignite than something that has already been charred once.

You realize that a Fresnel is thin,irrespective of focal length?
If you want to make the focus length smaller, you just have to
redesign the lens. No need to stack.

It gets difficult for a Fresnel lens to be anything faster than f 0.2
because the ridges start to interfere with the light path to the outer
edges of the aperture. Aberrations also get really bad at fast f ratios.

https://www.edmundoptics.com/f/fresnel-lenses/12434/

Commercial ones with decent optical performance tend to be expensive
unless they are mass produced for some other purpose.

Flat OHP condenser lenses are a good source of cheap big fast ones.
--
Martin Brown

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

In article <10jaut7$16l4g$1@dont-email.me>,
Martin Brown <'''newspam'''@nonad.co.uk> wrote:

Commercial ones with decent optical performance tend to be expensive
unless they are mass produced for some other purpose.

For the purpose of emergency fire starting, half decent lenses are okay.

Flat OHP condenser lenses are a good source of cheap big fast ones.

There is a guy publishing experiments with the optics of a flat tv
screen on youtube.

Martin Brown

Groetjes Albert
--
The Chinese government is satisfied with its military superiority over USA.
The next 5 year plan has as primary goal to advance life expectancy
over 80 years, like Western Europe.
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 07/01/2026 11:45, albert@spenarnc.xs4all.nl wrote:

In article <10jaut7$16l4g$1@dont-email.me>,
Martin Brown <'''newspam'''@nonad.co.uk> wrote:

Flat OHP condenser lenses are a good source of cheap big fast ones.

There is a guy publishing experiments with the optics of a flat tv
screen on youtube.

Do you mean from the venerable Sinclair TV80 flat screen portable TV?

One of my friends won one on the first ever edition of Krypton Factor.
--
Martin Brown

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 1/7/26 12:54, Martin Brown wrote:

On 07/01/2026 11:45, albert@spenarnc.xs4all.nl wrote:

In article <10jaut7$16l4g$1@dont-email.me>,
Martin Brown-a <'''newspam'''@nonad.co.uk> wrote:

Flat OHP condenser lenses are a good source of cheap big fast ones.

There is a guy publishing experiments with the optics of a flat tv
screen on youtube.

Do you mean from the venerable Sinclair TV80 flat screen portable TV?

One of my friends won one on the first ever edition of Krypton Factor.

There are pretty decent polarizer sheets in LCD screens. Using
these, I discovered that certain Chinese brands of polyester
rulers make fair quarter-wave plates. Build your own quantum
optics experiments for free!

Jeroen Belleman
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 07/01/2026 12:03, Jeroen Belleman wrote:

On 1/7/26 12:54, Martin Brown wrote:

There are pretty decent polarizer sheets in LCD screens. Using
these, I discovered that certain Chinese brands of polyester
rulers make fair quarter-wave plates. Build your own quantum
optics experiments for free!

One of the cuter physics demos with polarisers is to create an image in
clear Sellotape on an OHP slide and then cross them to do the reveal.

You have to calibrate your choice of tape and number of layers.

I used a child's drawing of a house.

In the bad old days long before thin film deposition they used to make research grade H-alpha filters out of a stack of layers optically clear calcite crystals and highly polished optically flat quartz wave plates.

They were very difficult to make and horrendously expensive!
--
Martin Brown

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