What kind of filter is this?

[sporgo]

I have been tinkering around with my webcam with the IR filter removed to get a sort of night vision effect. I have this old massive vhs camcorder which I was also tinkering with, so I thought I would open it up and see what its IR filter looks like. When I finally got in there to it I discovered that it is some kind of powered filter. It has four little leds which glow faintly green when powered on. Anyone know what the purpose of this is?

**broken link removed**

**broken link removed**

These old cameras have an unbelievable amount of circuitry crammed inside of them.

 

[duffy]

What the heck? Green leds? Does the filter itself sit flat against the imaging plane, right on the CCD element?

 

[sporgo]

Yes it does sit right against the ccd, in fact it clips directly onto the end of the ccd housing. This camera does not have any night modes or anything of that sort. I tried looking around online but could not find anything about it.

 

[duffy]

I'll be damned. Can you describe the effect when you switch it on looking at a heavy IR source like a fire or something?

 

[sporgo]

Well I cant do that any longer since parts of this thing have now been cannibalized for another project. I did aim it at some bright lights back when it was working but nothing special happened. I will try pointing my webcam through it while its powered up and see what it looks like.

 

[duffy]

There are a number of optically interesting compounds that use a shorter wavelength to power an effect that happens at a longer wavelength. An "IR test card" is one example - charge it with blue or green and it responds to IR with emission in visible wavelengths.

There are also compounds that darken at visible wavelengths in response to shorter wavelength activation, like UV sensitive sunglasses.

Perhaps the former effect is being used to achieve the latter.