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IR question

Discussion in 'Night Vision Optics and Illumination' started by Whistler, Dec 19, 2013.

  1. Whistler

    Whistler Donator

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    Sorry if this has been covered :eek: As a simple chap I thought NV was totally invisible to quarry, but the IR torches I have seen still emit a red glow, which is obvious to me and I assume to quarry ?

    I seem to remember reading something about "black IR" torches, is the beam from these "invisible" or does it just not work like that :confused:

    If its all been covered before, no need to repeat - just point me in the right direction for my education :D

    Thanks
     
  2. r10hunter

    r10hunter Honorary Member

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    940nm ir is invisible. But most sensors work far better with the 840nm that gives off the slight red glow from the illuminator.
    I have a yukon ranger pro that uses 940nm ir, that says in the instructions that it uses a pulsed beam to get range so this is not really the kind of thing that will work on a DIY setup.
    If you use just enough ir with the 840nm setups it's not a problem.

    Also only move slowly when the illuminator is on and don't leave it on more than needed. I also find a larger torch head with a dull large glow is better than a small torch head with a bright point of light.
    Cheers Andy
     
  3. terry1001

    terry1001 Major Poster

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    It's worth mentioning again, the light sources emit light which consists of a range of wavelengths. The coloured led emitters (including ir) emit a fairly narrow spectrum of light but there will be some outside of the specified one. The 850nm ir emitter will contain a tiny amount of visible red. Each persons eyes vary in sensitivity to the various wavelengths and what is quite visible to one person will be invisible to another.
    If you illuminate something with ir light you won't see anything at all so the 'beam' itself is invisible, if you look back at the torch you will probably see a red glow which is fairly faint. Rabbits are not supposed to be able to see red light at all although it does seem clear that a bright red light can spook them but this may be more to do with the way the light is used rather than the colour itself.
    The most common illuminators emit 850nm ir light which is what most of the cctv cameras are tuned to but you can also get 940nm emitters. Unfortunately the cameras are much less sensitive to this wavelength and so your range is reduced by quite a lot, probably at least 50% depending on the camera/lens/scope. These wavelengths are in the 'near infra red' part of the spectrum and ir does continue beyond this but it becomes very specialised.
    The answer probably is that there are 'degrees of invisibilty' :)
     
  4. Chippy1988

    Chippy1988 Busy Member

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    Location:
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    I am going to try and use some un-exposed developed camera film as a ir pass filter, which should in theory let the ir through but have less of the red light emitted. The rabbits on my perm seem to be spooked by the red glow so thought it would be worth a try.


    atb James
     
  5. terry1001

    terry1001 Major Poster

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    I'll be interested to hear how you get on with this, are you going to put it in front of an ir led?
     
  6. Chippy1988

    Chippy1988 Busy Member

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    yes terry I intend to put it behind my t20 lens, if you look at commercial cctv ir they have a black glass in front, and apparently the camera film will do the same only cheaper.

    atb James
     
  7. terry1001

    terry1001 Major Poster

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    Yes the ir pass filters do appear to be black as they don't let any visible light through. I've heard of people using film negatives but haven't heard how successful they were. You can probably still buy the film that was designed specially for ir photography, I don't know if that is any different to the 'normal' film when developed unexposed. If it works ok you can buy the ir pass filters for photography quite cheaply on ebay and may well be able to get one the correct size to fit in your torch. These do come in several different wavelengths and the cheap sellers don't normally say what their product is, if you put a 940nm pass filter on a 850nm emitter you wouldn't get anything through.
     
  8. r10hunter

    r10hunter Honorary Member

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    This may help.
    [​IMG]
    Cheers Andy
     
  9. kenhawker

    kenhawker Honorary Member

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    Because you are mostly static (not moving around) whilst shooting you won't really spook your quarry. For instance when I go rat shooting I sit on my butt and shoot from a stationery position. But my ir will be dancing around as if it a firefly with its nuts on fire. And the rats have no idea that I'm there.
    Same with the bunnies but im on the move then.
     
  10. terry1001

    terry1001 Major Poster

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    That filter will pass some visible red light (<3% ) so there may still be a red glow visible. When I get a chance I'll look up the spectral output of the Oslon Black and see how much might fall into the slightl visible spectrum.
     
  11. kenhawker

    kenhawker Honorary Member

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    Terry have you got a link for a oslon black led and driver?.
    Cheers
     
  12. kev1299

    kev1299 Engaging Member

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    I've tried a piece of IR filter. Over an incandescent lamp, no visible light comes through, over an Oslon black the red is still clearly visible.
     
  13. terry1001

    terry1001 Major Poster

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    If you have a look here http://uk.mouser.com/new/osram/osramIRoslonblack/ you can find the data sheet for the Oslon Black - the 4715S version, it's the middle one of the 3 listed. On the data sheet it shows the spectral emission of the chip and there is virtualy no output below 700nm in percentage terms. However this is a powerful led and this tny amount will still be visible particulalry if the torch is zoomed to a narrow beam.
    You do have to be careful buying ir filters as there is seldom any indication of what wavelength they pass unless you spend a lot of money on one. If you get a 950nm version even a cctv camera won't see much especially if it has an ir cut filter on it to correct for the colour cast in daylight. These cameras are intended to be used with 850nm ir light.
    This type would be ol http://www.ebay.co.uk/itm/Infrared-...es_CameraLensesFilters_JN&hash=item35cea54351 but
    this type http://www.ebay.co.uk/itm/43mm-950n...es_CameraLensesFilters_JN&hash=item4ab05d1fd2 would not work very well at all.
    White lights, whether they are led, halogen, xenon or incandescent do not contain much ir light, if they are 'warm' colour lights and have a yellow tint then they will contain more red than the cool blue ones. Putting a filter in front of one of these light sources to get coloured light simply wastes a lot of the energy of the lamp, a dedicated emitter is more efficient.
     
  14. Whistler

    Whistler Donator

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    Wow, thanks chaps ! I'm using an NS200, so far very successfully, but when rat shooting the other night I left it switched on when I went to pick up - when I looked back the red glow was quite obvious. That's what got me scratching my head...
     
  15. terry1001

    terry1001 Major Poster

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    That's so that you can find your rifle again :up:
     

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