IR Question

[Team Member]

Correct me if I´m wrong, but the higher you go, for an example from 850nM to 940nM on an IR filter, the less output....?

What I´m looking for is a filter that has very little visible red light coming out from the IR filter. In military use it´s not too good if you turn on a red looking spotlight in the middle of the night when you don´t want to be seen at all

I have been looking at my Surefire M1 and that one is supposed to be 880nM. When I look directly into it I can see a red spot. But the flip-up IR filters that Surefire is selling is stated to be 1000nM and when I´m looking att them I don´t see a red spot...

I also have a IR filter for my Polarion PH50 but that is more looking like a dim, red spotlight when turned on. And I don´t know how many nM that filter is.


Sooo, what should it be? Or have I already an answer for my Q?

 

[csshih]

yup.
the "higher" the NM ratings, the greater the cutoff of light there will be.

after 940nm, there shouldn't be anything visible.. I think.

 

[purduephotog]

Correct me if I´m wrong, but the higher you go, for an example from 850nM to 940nM on an IR filter, the less output....?

What I´m looking for is a filter that has very little visible red light coming out from the IR filter. In military use it´s not too good if you turn on a red looking spotlight in the middle of the night when you don´t want to be seen at all

I have been looking at my Surefire M1 and that one is supposed to be 880nM. When I look directly into it I can see a red spot. But the flip-up IR filters that Surefire is selling is stated to be 1000nM and when I´m looking att them I don´t see a red spot...

I also have a IR filter for my Polarion PH50 but that is more looking like a dim, red spotlight when turned on. And I don´t know how many nM that filter is.


Sooo, what should it be? Or have I already an answer for my Q?

You don't say what your source is- I'm assuming LED?

Filters are 'band pass'. That means that, at some wavelength, they will pass (or block) 90% of the photons of a certain frequency and higher/lower.

What you're looking for is a deep IR filter. You can get them from a number of sources- you can even image through them.

If I may suggest take a look at this page:
http://www.edmundoptics.com/onlineCatalog/DisplayProduct.cfm?productid=1918

This particular filter starts passing IR at 675 and goes up to 800 for 100%. Since you want a deeper filter than that the cost is definitely going to go up.

This page will detail specific start wavelengths-
http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=2683

They're expensive.

These guys will also do the trick, but there is a fair amount of leakage.
http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=1512&StartRow=21&PageNum=2
They're also significantly cheaper than above.

The 'young man' eyeballs can see the IR leaking out of a filter better than the older folks. I have lost almost all of my IR sensitivity and I'm 33. Guys in the military will have the highest accuity- but even then the visibility falls off by 1/r2 so that by any appreciable distance the light will not be visible by human eyes. It is a tradeoff.

I'm also assuming you are not really going to use this in the military because anyone with even a cheap pair of modified IR goggles would pick that pulse of IR up at a range far enough to reach out and tap you on the 'noggin. If you are, I'd ask that you talk to your CO and clarify it's use- yes I'm a contractor working with these sorts of systems.

Anyway... hope it helps!

 

[ZDP189]

In military use it´s not too good if you turn on a red looking spotlight in the middle of the night when you don´t want to be seen at all

In military terms, one wouldn't want to be emitting any IR wavelength at all, seeing as every man and his dog are carrying intensifiers.

Unsuspecting girlfriends however, can't see the further wavelengths. Unless they also have night vision.