I’ve got a Zenit (Russian brand, available just after the USSR tanked) first generation Image Intensifier. I just put new batteries in it, and with the lens cap on, pushed the button that powers it up. And I could see what it was pointed at, ghostlike and blurry, but nevertheless identifiable, THRU THE FUCKING LENS CAP!!ONE1!!
After a few (not very scientific, admittedly) experiments, it seems that the black lens cap is still transparent to far-infrared. I had my mother put a finger on one of the keys of her computer keyboard for a few seconds, and I was only one key off. While still looking thru the thing, I saw my own footprints where I’d walked to her room, when I went back through the dark living-room. Black dogs and black or black-and-white cats don’t show up. Their fur is far-infrared opaque, apparently. They are dark blurs on a warmer background.
Is the lens cap polyethylene? Polyethylene is pretty transparent to the thermal infrared. In fact, lots of cheap IR lenses, like the fresnel lenses on motion detectors, are made of it.
My father bought it probably in '91 or 2. I have no idea where. I inherited it when he died in '96, because no-one else wanted it, and if I attached it to my 120 mm telescope with my camera mount, it would give equivalent to something approaching 200mm in limiting magnitude, so I fucking wanted it. It worked. I saw a comet that was only visible in an 8" scope. Cool shit. Plus, I’ve looked at wildlife in the dark with it, since, and spied on my neighbors when they were having an argument outside with the lights off, once, but I really haven’t used it much. I just put fresh batteries into it, tonight, and with the lens cap on, powered it up, and found out I could actually see identifiable shit with that lens cap on. WTF??? So I tried to figure out why. It would seem to be because the lens cap is transparent at far IR.
I’ve got a wide range of IR LEDs I can test with. Both of my digital cameras go down to at least 940…
I wonder how low this thing goes.
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Damifino. It don’t fucking know, Wanna test it? I’ve got one. but it was Russian military, circa late 80’s would be my guess. It was for sale to people like my father in '91 or so. Whatever amplification ratio he could by about then, would be my half-assed guess. I’m guessing he never found out about the far-IR ability to see through the fucking black lens caps.
Oh, yeah. I haven’t the vaguest idea. All I know is it’s black. But, given this result, it’s probably rather transparent at far IR frequencies. I’m looking forward to bending the shit.
The lens cap is there to protect the lens from being scratched or damaged. It would also prevent sunlight from entering the unit and over cooking some component. Same as with binoculars, cameras, etc.
It shouldn’t matter to an IR sensor what color the cap is. What would matter is whether or not the material the cap is made of effectively blocks heat or infrared radiation.
Yeah. I don’t know. I’m rather shocked that it will see thru the fucking lens cap. I took it off, but it was just before sunset. I damn near blinded myself.
Time to dig out my various IR LEDs, and see what it responds to. That fucker responds to far lower IR, with an actual image, than any of my digital cameras will.
A surprising number of things that are black to the human eye are transparent in the IR. I always back my lens caps up with a metal plate when I want to be sure that I’m blocking IR light from entering.
My mother just corrected me. Dad didn’t buy it in '91 or '92, he bought it in '01 or '02. I still have no idea where he bought it. And I couldn’t have bought one for myself until '06, when I bought my telescope from the money I inherited from him. I still didn’t have enough to get one for myself, but he’d already bought one, so I didn’t need another.
