Efficiency of cheap macro lenses at near infrared?

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?

On 22/11/2011 8:34 a.m., 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?


Perhaps this helps:
http://dpanswers.com/content/irphoto_lenses.php
Macro may not be the way to go, on this list Nikon and Canon 50mm f1.8
lenses are cheaper and larger aperture than typical macro lenses (f2.8).
If longer focal length is needed, then a cheap mirror telephoto lens
might be perfect. Slower aperture, but you can get 500mm focal length
very cheaply, also you can focus visible light from the source to the IR
sensor, and not have to offset this for IR.

On 21/11/2011 19:34, 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?

If you only need a couple why not get a simple planoconvex lens from any
of the generic suppliers or surplus shed (for about $5).

http://www.surplusshed.com/lens.cfm

You don't need a fancy achromat for this sort of thing your source is
close to monochromatic +/- 30nm - though you might need a slightly
clever baffled optical design and an IR pass filter if the thing has to
work well in daylight. You might even get away with a Fresnel reading
lens or bits taken from an old redundant OHP.

--
Regards,
Martin Brown

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.

--
Peter

PeterN 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?

mianileng wrote:

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 second the recommendation for www.surplusshed.com.
Practically any glass should be fine at that wavelength,
and the ones that aren't would be fairly exotic. A simple
plano-convex or positive meniscus lens should be fine since
you only have one wavelength to focus.

The very cheap "educational optics" tend to be soda-lime
glass. Most of the rest are probably borosilicate glass,
but it shouldn't matter for your purposes.

Peter.
--

Me wrote:
On 22/11/2011 8:34 a.m., 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?


Perhaps this helps:
http://dpanswers.com/content/irphoto_lenses.php
Macro may not be the way to go, on this list Nikon and Canon
50mm f1.8
lenses are cheaper and larger aperture than typical macro
lenses
(f2.8). If longer focal length is needed, then a cheap mirror
telephoto lens might be perfect. Slower aperture, but you can
get
500mm focal length very cheaply, also you can focus visible
light
from the source to the IR sensor, and not have to offset this
for IR.

Thanks for your interest. Your reply made me realise that I left
out something, namely that the macro lenses I'm considering are
not SLR compound lenses, but one of the simple $3 add-on
attachments. A $1 magnifying glass would also do - provided that
it passes IR well enough, except that it will be easier to secure
a lens with a standard thread to the front of the receiver box
and to attach an IR filter once the focusing's done with visible
light.

Yes, I'd intended to do just what you suggest about focusing with
visible light and then adding an IR-pass filter. The offset in
focal plane wouldn't matter even for a shorter focal length
because I'd planned to leave it somewhat out of focus anyway.
This is because
1) the sensor area is about 0.2in in diameter and spreading the
IR image will reduce the possibility of overheating a spot when
it's tested at closer range,
2) it will compensate for slight misalignment, albeit with some
loss in efficiency. It's a trade-off between the two.

My calculations allow for some loss of efficiency from spreading
the image to an area somewhat larger than the sensor, from
absorbtion by the intervening 400m of air and by the glass. The
question is how much loss the last one will contribute.

Martin Brown wrote:
On 21/11/2011 19:34, 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?

If you only need a couple why not get a simple planoconvex lens
from
any of the generic suppliers or surplus shed (for about $5).

http://www.surplusshed.com/lens.cfm

You don't need a fancy achromat for this sort of thing your
source is
close to monochromatic +/- 30nm - though you might need a
slightly
clever baffled optical design and an IR pass filter if the
thing has
to work well in daylight. You might even get away with a
Fresnel
reading lens or bits taken from an old redundant OHP.

You're quite right about not needing a fancy lens. In fact, I'd
intended to use one of those simple $3 add-on lenses _and_ an
IR-pass filter. Please see my reply to "Me" for details.

PeterN wrote:
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.

Not at all. This is for a very professional job. It's an
expansion of custom-designed equipment that I built two years ago
and has been in use since then. I like to use standard, cheap and
readily available material wherever possible and pass on the cost
savings to my customers.

Peter Irwin wrote:
mianileng wrote:

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 second the recommendation for www.surplusshed.com.
Practically any glass should be fine at that wavelength,
and the ones that aren't would be fairly exotic. A simple
plano-convex or positive meniscus lens should be fine since
you only have one wavelength to focus.

The very cheap "educational optics" tend to be soda-lime
glass. Most of the rest are probably borosilicate glass,
but it shouldn't matter for your purposes.

Thanks for your interest. As I said in reply to "Me", I forgot to
mention that I did intend to use a cheap add-on lens rather than
some SLR glass.