Infrared still image projector

Hi. I'm a newbee & not too electronically literate so please expand your abbreviations to help this dummy. I'd like to build a small simple Infrared still image projector like a photographic slide projector but IR only. It doesn't need to be too powerful as I'll only use it in total darkness to project the image about 3 feet. I'm guessing that some IR LEDs would probably provide enough light but I don't know anything about a suitable reflector or lens or how & where to mount my transparency image in the device. I don't want to modify a stills projector & want something much smaller. Is there something small I could buy & modify the light source maybe ? Thanks for your patience in advance.
I'm helping somebody with their project involving Night Vision/Thermal imaging equipment. Can't say any more than that because it's not really my project.
I don't understand your difficulty associating IR & darkness ? What use could IR be in an illuminated environment ? Edumacate me here please. lol I'll probably learn something from your question if I better understand it.


2004-07-25 10:06 pm
since you are projecting IR range wavelengh, it does not matter if the room is iluminated or not. Think of UV wavelengh range for instance, we can´t see it either.

yes, that was a good question, what would you (your friend) use as trasparency?, i guess something that passes IR and blocks IR where you want... will be hard think to work out...

good luck
Thanks so much for your imput guys (& gals ?). Like I said before I hope to learn something here. I've used an IR LED & it's IR emission is able to pass through glass & transparent thermoplastic much the way visible wavelength light does. It is also blocked by opaque objects & coatings. Why wouldn't a negative monochrome transparency (black surround & transparent image) give me an IR projected image ? Am I missing something here or are we on differing wavelengths ? pardon the pun.
If you want to see the "infrared world", take an older Sony camcorder with nightshot, add an ir pass filter over the lens, and the camera will only see ir light. The camera will turn the ir light into a visible recorded image. In fact, all ccd imaging devices can "see" ir light. Go outside on a nice sunny day with it and start filming in nightshot mode. Now play it back on a projector. I even have an ir filter for my digital camera, the images it captures are very surreal looking.
Thanks for the reply - 10mm sq is easy. I could go to 30mm sq if required. Do you maybe mean 10cm sq ? - 4" ? - Hope not.
I'd like to project at about 40 degrees total included angle of projection though. This might be a problem.
What sort of 'small hand held projector' do you have in mind ? Any idea what lens I'd require if I wanted to use a bank of IR LEDs ?

BTW - This Ashes series is pretty exciting eh ? I'm impressed. It's about time you Poms (no offense intended) taught our cricketers how to win (or lose) with grace. I'm ashamed of the lack of dignity our team has shown in their dominance. Good luck. Care for a cyber wager ?
is it really black?

>Why wouldn't a negative monochrome transparency (black surround & transparent image) give me an IR projected image ?

It might, or it might not: It all comes down to the wavelengths the "black" part of the transparency blocks. You may perceive some film as being black, even if it passes IR. Black is just the absence of any energy that would stimulate your retina's red, green, or blue sensors.

For example, if you put Wratten blue and red filters together, they will block all visible light. But since these filters do not block IR, the combination will give you an IR pass filter.

If you decide you need a stronger IR source, you could use a standard halogen lamp with such an IR pass filter. Halogen lamps put out a broad spectrum of IR, while IR LEDs put out a single wavelength. The LED "looks" bright to a narrow-band sensor, but your application may be able to use a wider bandwidth.

Another terrific IR source is the sun! Most IR communication systems are completely swamped by the IR content of sunlight, even on a cloudy day in the shade.
Thanks Guy. I'm just beginning to understand IR. For instance I discovered that Quartz Halogen tube shaped lighting elements were the most efficient heaters of the opaque thermoplastics I commonly use in a large vacuum forming machine I just built. Expert advice would have me believe that ceramic or other expensive heaters were the go but over lunch at a seminar the owner of a German Manufacturing Company of plastics machinery showed me some research his Engineers had done & saved me thousands. Only minor hitch is that this machine won't even warm transparent thermoplastics.
Back to the subject at hand - I need to do some homework on understanding the IR spectrum. Can you suggest a short concise text or source of this information please.
For the application at hand I like the idea of avoiding heat generating incandescent bulbs & also the lower (?) power consumption of LEDs. The equipment needs to be portable.
Am I going to have focussing difficulties if I use a bank of LEDs rather than more of a 'point source' typy of the IR generator like a halogen lamp & filter ? The image projection is short distance & low intensity.
The term 'infra red' covers quite a range of wavelengths, and you need to establish which part of the spectrum your application requires.
I like the idea of avoiding heat generating incandescent bulbs
OK, but that heat is mainly infra red - i.e. they are one and the same thing - but of a different frequency from that emitted by, say a remote control transmitter. A good start might be to Google 'black body radiation'. Depending on the part of the spectrum which interests you, you may need specialised optics. Standard lenses are OK for the shorter-wave radiation though, but their effective focal length will be rather different than for 'white' light, and aberrations will not be as well corrected.
I realise that patents, etc. might get in the way, but a bit more description of your application (how the IR image is to be detected, for example) would help us to help you:)
OK Thanks for your input. The image I intend projecting is to be viewed in total darkness - for example to test night vision/thermal imaging equipment. When I observe the TV remote controller beam through my night vision monocular or it's reflection in a mirror or on the wall it's behavoiur seems no different from visible light.
I don't have the experience or training yet to understand why this form of light wouldn't be blocked/attenuated when passing through a transparent film with a negative image printed on it in say - black ?
I've just located a still image visible light projector to experiment with. My idea is to replace the bulb with IR LED(s).
Can you explain the IR 'near/far' description of this spectrum, it's wavelengths, optical behaviour etc ?
I'll do that Google & see if I can find the relevant info there too.

Lots of posts on other threads in this forum discuss the use of LEDs as a light source for projection. The theoretical answer is yes, you could replace the lamp with a high-powered LED. But you would have to use an LED that matched the emission pattern of the original lamp, to get light to all parts of the LCD. Like maybe a chip LED without the usual plastic lens.

From a practical viewpoint, the answer is no, unless you can use a VERY dim projection. Or get a high-powered IR laser diode and change the optics quite a bit to spread the narrow beam out to light the whole LCD. But if I had such a narrow beam IR laser, then I would forget the LCD and just use spinning mirrors to scan the beam across the screen, and modulation to vary the intensity to form the image.