Efficiency of cheap macro lenses at near infrared?

On 11/21/2011 10:35 PM, Rich wrote:
wrote in news:4ecaf9cc$0$13254
:

On 11/21/2011 2:34 PM, mianileng wrote:
This does not directly involve photography but I thought the
people here would be knowledgeable enough about the subject to
help.

I'm working on an electronics project for which I'd like to have
an inexpensive way of focusing incoming infrared rays onto a
sensor. The radiation is from a distant emitter, a bunch of
infrared LEDs sending coded pulses of IR energy from about 400m
(1300 ft) away. The project is for non-photographic work and
optical quality is not important. What *is* important is an
efficient concentration of the IR energy and I thought of using a
cheap macro lens of about +10 dioptre.

The LEDs operate at 940nm. Transmission curves at the following
link for soda lime, borosilicate and UV glasses indicate quite
good transmissivity (for my purpose) at that wavelength.
http://www.sinclairmfg.com/datasheets/optical3.html
So far I haven't found comparable data for the glass used to make
the cheap lenses I mentioned. Can anyone please provide some
information about that?



This has the aroma of a homework project.


So what if it is? So the guy might be asking for information he hasn't
been able to find elsewhere? Would helping him out KILL you, sourpuss?

Have you ever heard of intellectual integrity? If I had a deep knowledge
of the area I might steer him. But, I would not supply the answer.

BTW your informed answer is striking by its absence.


--
Peter

RichA wrote:

If you don't care about edge definition, just the centre, and you can
find one of the right focal length, a quartz lens element will work as
it will pass IR.

For what he wants, a toy magnifying lens will do just fine.
Just about any glass is transparent at 940nm infrared. Finding
a glass that wasn't would require something exotic.

He doesn't need colours brought to a common focus because
he is using monochromatic infrared. He needs to be able to adjust
focus to give him the best output from his device, but a single
element lens will be fine.

Quartz lenses are mostly used for ultraviolet. Ordinary
glass will pass near-UV tolerably well, though many camera
lenses made in recent decades filter even that. Quartz
passes a very wide UV spectrum. Ordinary glass passes
quite a lot of infra-red.

Peter.
--

On 11/22/2011 8:41 AM, RichA wrote:
On Nov 22, 5:59 am, wrote:
On 11/21/2011 10:35 PM, Rich wrote:









wrote in news:4ecaf9cc$0$13254
:

On 11/21/2011 2:34 PM, mianileng wrote:
This does not directly involve photography but I thought the
people here would be knowledgeable enough about the subject to
help.

I'm working on an electronics project for which I'd like to have
an inexpensive way of focusing incoming infrared rays onto a
sensor. The radiation is from a distant emitter, a bunch of
infrared LEDs sending coded pulses of IR energy from about 400m
(1300 ft) away. The project is for non-photographic work and
optical quality is not important. What *is* important is an
efficient concentration of the IR energy and I thought of using a
cheap macro lens of about +10 dioptre.

The LEDs operate at 940nm. Transmission curves at the following
link for soda lime, borosilicate and UV glasses indicate quite
good transmissivity (for my purpose) at that wavelength.
http://www.sinclairmfg.com/datasheets/optical3.html
So far I haven't found comparable data for the glass used to make
the cheap lenses I mentioned. Can anyone please provide some
information about that?

This has the aroma of a homework project.

So what if it is? So the guy might be asking for information he hasn't
been able to find elsewhere? Would helping him out KILL you, sourpuss?

Have you ever heard of intellectual integrity? If I had a deep knowledge
of the area I might steer him. But, I would not supply the answer.

BTW your informed answer is striking by its absence.

--
Peter

I never claimed to have an answer, you dour old man.

Oh! That is clever.

--
Peter

"mianileng" wrote:
This does not directly involve photography but I thought the
people here would be knowledgeable enough about the subject to
help.

I'm working on an electronics project for which I'd like to have
an inexpensive way of focusing incoming infrared rays onto a
sensor. The radiation is from a distant emitter, a bunch of
infrared LEDs sending coded pulses of IR energy from about 400m
(1300 ft) away. The project is for non-photographic work and
optical quality is not important. What *is* important is an
efficient concentration of the IR energy and I thought of using a
cheap macro lens of about +10 dioptre.

The LEDs operate at 940nm. Transmission curves at the following
link for soda lime, borosilicate and UV glasses indicate quite
good transmissivity (for my purpose) at that wavelength.
http://www.sinclairmfg.com/datasheets/optical3.html
So far I haven't found comparable data for the glass used to make
the cheap lenses I mentioned. Can anyone please provide some
information about that?

I saw a similar project many years ago. I thought they used a tube to
reject outside interference.
It would seem dependent on sensor. Is it one inch wide or one mm wide, or
microns ?

Greg

gregz wrote:
"mianileng" wrote:
This does not directly involve photography but I thought the
people here would be knowledgeable enough about the subject to
help.

I'm working on an electronics project for which I'd like to
have
an inexpensive way of focusing incoming infrared rays onto a
sensor. The radiation is from a distant emitter, a bunch of
infrared LEDs sending coded pulses of IR energy from about
400m
(1300 ft) away. The project is for non-photographic work and
optical quality is not important. What *is* important is an
efficient concentration of the IR energy and I thought of
using a
cheap macro lens of about +10 dioptre.

The LEDs operate at 940nm. Transmission curves at the
following
link for soda lime, borosilicate and UV glasses indicate quite
good transmissivity (for my purpose) at that wavelength.
http://www.sinclairmfg.com/datasheets/optical3.html
So far I haven't found comparable data for the glass used to
make
the cheap lenses I mentioned. Can anyone please provide some
information about that?

I saw a similar project many years ago. I thought they used a
tube to
reject outside interference.
It would seem dependent on sensor. Is it one inch wide or one
mm
wide, or microns ?

The sensor is a commercial module of the type used in consumer
remote control receivers. The sensitive area is about 0.2" in
diameter. For other applications where the distance between
transmitter and receiver are much less (up to about 70 ft), I use
a single IR LED transmitter and a tube at the receiving end to
minimize the effects of ambient light. This one will operate at
nearly 20 times the distance and hence 400 times weaker
intensity. Even after boosting the transmitter output by using
multiple LEDs, there will still be a need to concentrate the
received radiation. That's where the lens comes in.

On 11/22/2011 12:41 PM, RichA wrote:
\ Glad you enjoyed it, now why are you still reading what I post? Lead
by example.

You are a sad example of an individual who desperately needs help.

But unlike Brucie, I don't claim to bury my head in the sand.
In fact, Brucie has claimed to plonk so many people, that his comments
have become irrelevant.


--
Peter