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#1
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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? |
#2
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Efficiency of cheap macro lenses at near infrared?
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. |
#3
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Efficiency of cheap macro lenses at near infrared?
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 |
#4
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Efficiency of cheap macro lenses at near infrared?
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 |
#5
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Efficiency of cheap macro lenses at near infrared?
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? |
#6
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Efficiency of cheap macro lenses at near infrared?
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. -- |
#7
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Efficiency of cheap macro lenses at near infrared?
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. |
#8
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Efficiency of cheap macro lenses at near infrared?
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. |
#9
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Efficiency of cheap macro lenses at near infrared?
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. |
#10
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Efficiency of cheap macro lenses at near infrared?
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. |
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