Can a thermal sensor see through a glass lens?

[AndreusMaximus]

So this question is based merely on curiosity and not on any practical reason to know, but my question is, can a thermal sensor see through a glass lens?

As I understand it, thermal imaging uses a sensor to detect the heat of any object it is pointed at by picking up on the infrared radiation that all objects that have heat put off.

So if you tried to look through a rifle scope, for example, with a thermal sensor (specifically a thermal sensor, NOT a night-vision sensor which amplifies low levels of visible light) what would happen? Would the thermal camera just pickup the temperature of the glass lens, and thus render the optic essentially opaque to the sensor? Or does glass refract the infrared radiation the same way it does visible light, thus making the optic work just the same for a thermal sensor?

 

[foszoe]

When I have tested double paned windows, it reads the surface temp of the glass.

 

[Rookie]

Nope. It reads the temperature of the object in front, not behind.

 

[42769vette]

You can see your reflection, but nothing on the other side

 

[gds]

Ditto !

 

[ZurokSlayer7X9]

Allegedly it is possible to see through a scope with a thermal sensor, however the scope can't use conventional glass, but must use a specialized crystalline silicon or something. I'm not an expert, but I believe this has something to do with glass blocking the longer wavelengths used by thermal sensors. It is also why IR lasers and lights won't be picked up by a sensor, as they transmit photons at a much higher wavelength.

 

[AndreusMaximus]

Allegedly it is possible to see through a scope with a thermal sensor, however the scope can't use conventional glass, but must use a specialized crystalline silicon or something. I'm not an expert, but I believe this has something to do with glass blocking the longer wavelengths used by thermal sensors. It is also why IR lasers and lights won't be picked up by a sensor, as they transmit photons at a much higher wavelength.

Interesting. I didn't know that about IR lights or lasers, either, but that makes sense.

 

[ZurokSlayer7X9]

Interesting. I didn't know that about IR lights or lasers, either, but that makes sense.

I forgot to give the caveat of "in my experience". My thermal will not pick up either my IR laser, or any IR security cameras that I tested it on. However, while I was fact checking there was a mention that in certain situations you could see something. If that one anecdote is correct, this is how I might not be seeing IR stuff with my thermal:

Infrared has a spectrum like visible light. Roughly 700 nanometers to 1 millimeter. While the visible spectrum is divided into red, yellow, blue, etc., so is infrared (near infrared, mid-wavelength, far, etc.) Most IR stuff maybe operates in the Near range, while thermal sensors are "colorblind" to anything not in the Far range. For the record, thermal radiation is around 7-14 micrometers.

It's surprisingly very difficult to research that because too many people call thermal sensors "IR cameras or scopes". Too many sites saying you can see IR, only to find out they're talking about IR imaging (PVS-14, digital night vision, etc.) and not a freaking thermal sensor.

 

[Brandon]

My fluke thermal imager can't "see" through glasd.

Take that for what it is worth.

 

[BR8818]

No, you'll only see a reflection.

 

[AndreusMaximus]

I forgot to give the caveat of "in my experience". My thermal will not pick up either my IR laser, or any IR security cameras that I tested it on. However, while I was fact checking there was a mention that in certain situations you could see something. If that one anecdote is correct, this is how I might not be seeing IR stuff with my thermal:

Infrared has a spectrum like visible light. Roughly 700 nanometers to 1 millimeter. While the visible spectrum is divided into red, yellow, blue, etc., so is infrared (near infrared, mid-wavelength, far, etc.) Most IR stuff maybe operates in the Near range, while thermal sensors are "colorblind" to anything not in the Far range. For the record, thermal radiation is around 7-14 micrometers.

It's surprisingly very difficult to research that because too many people call thermal sensors "IR cameras or scopes". Too many sites saying you can see IR, only to find out they're talking about IR imaging (PVS-14, digital night vision, etc.) and not a freaking thermal sensor.

Yep. I've been consistently surprised how difficult it seems to be to look up basic questions about thermal/infrared/nightvision due to the constant misuse and misunderstanding of different terms involved, and the way those terms overlap with each other. Glad to hear from someone who actually has experience using the technology.

I really hope to make the dive into thermal someday myself, but right now it's just not realistically in my budget, and I don't want to try to squeeze in something cheap that would just turn out to be trash. So for now I'm just being curious.

 

[ZurokSlayer7X9]

Yep. I've been consistently surprised how difficult it seems to be to look up basic questions about thermal/infrared/nightvision due to the constant misuse and misunderstanding of different terms involved, and the way those terms overlap with each other. Glad to hear from someone who actually has experience using the technology.

I really hope to make the dive into thermal someday myself, but right now it's just not realistically in my budget, and I don't want to try to squeeze in something cheap that would just turn out to be trash. So for now I'm just being curious.

When I first got a Gen 3 PVS-14, I was blown away. When I got my ATN Thor, I was blown away even more. The thermal was just way better at night vision than the PVS-14. Some advice however, be sure to get the magnification you want, and pay attention to the FOV. I got a 5-10x scope, and while I have seen a mouse scurrying in a field 100 yards away at midnight, the scope is unusable at 25 yards or less. If I had to go back and do things over, I would get one with a base magnification of 1x with a higher FOV that could zoom to higher magnifications. Second is be aware that NVs can have much longer battery life vs. thermals. (55 hours for PVS-14 vs. 4 hours lithium for ATN Thor) A lot of thermals last around an hour.

 

[Rookie]

2.5-3 native is just about perfect assuming you have a 640 core. It gives you a wide field of view and allows you to zoom for longer shots without having a horrible picture. My scope is 4.5 native, but my scanner is 3. I typically take the 150+ yard shots and my hunting partner takes the 150- yard shots with his 2.5 native.

My thermal scope will last about nine hours on a single charge. My scanner lasts about 4 hours.