The Shape and Size of Glare Around Bright Lights

Ravi

Senior Member.
20mm, 2mm thick, for 20 bucks. Not bad! Be careful with them, is my advice. If you drop em, they crack.
 

Mick West

Administrator
Staff member
20mm, 2mm thick, for 20 bucks. Not bad! Be careful with them, is my advice. If you drop em, they crack.
It's unpolished. But I've got a polisher, and it will be interesting to see how well it works without polishing. I was quite surprised what a good image you get reflected from a matt metal surface, so maybe a window might work somewhat with not polishing.

Here's a metal surface reflecting my hand in thermal IR.
Metabunk 2020-09-12 12-53-57.jpg

But, it's matt, with near-zero specular reflectivity.
Metabunk 2020-09-12 12-56-33.jpg
 

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Ravi

Senior Member.
Nice example!

It's of course all due to the use of long wavelengths. You need half-lambda surface quality to make a "mirror", for IR of say 10 um, this comes down to 5um, which is what likely is the surface roughness of the metal part shown.
 

Itsme

Active Member
When looking at jet engines in IR, another factor besides glare comes into play.

The elongated hot exhaust plume itself is a source of IR radiation as well. So the black (or white) blob that you see when looking directly at the back of the jet will also be caused by the exhaust plume, which is a rather thick cloud of hot gas from that line of sight (looking directly into the end of the exhaust plume). The IR image from that hot gas will of course not rotate in the gimbal case.

The images showing rotating glare in IR and visible light can be a bit misleading in that sense, since they only show glare.

The images demonstrating glare from jet engines do show the typical spikes radiating out, which indeed do rotate with the optics, but the center of the blob does not since it is a thermal image of something physical (a hot exhaust cloud), not glare.
 

Mick West

Administrator
Staff member
The images demonstrating glare from jet engines do show the typical spikes radiating out, which indeed do rotate with the optics, but the center of the blob does not since it is a thermal image of something physical (a hot exhaust cloud), not glare.
Can you show an example of what you mean?
 
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