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Calculate thermal camera lens specifications of Flir B4xx T4XX E6X


I recently aquired a B4xx thermal camera with a broken front lens.
I found a few suppliers that would make a custom coated germanium lens.
They are just asking me for the specs of the lens , does anyone have them?
From what i can gather it's a 25mm diameter wide positive meniscus lens (concave convex).
I would be grateful if anyone has specifications of that frontal lens.
All T4XX B4XX and E6x series cameras use the same type front lens element.

FLIR do not release the lens block element specifications, even to service centres. They have no reason to do so. Sadly you are on your own with this challenge. If you have all the parts of the shattered lens you could reassemble it with adhesive and carry out lens tests using your working thermal camera for beam output observation and a thermal target source to illuminate the lens. No different in principle to testing a visible light lens to establish its basic optical specifications. You can also place the unknown lens in front of a thermal camera that has had its lens removed and make tests using that method.

You could also try using a micrometer to measure the profile of the meniscus compared to the profile of the front face but this is fraught with issues as lenses can have complex profiles. It is better to optically profile the lens.

I considered buying this camera but the shattered lens was too much work to rectify for it to make sense in my case. I considered trying the front lens elements from various spare thermal camera lenses that I own to see whether one was a close enough match to work with the other lenses in the lens block. It is the internal focus design that would present a significant challenge to this approach. Even if I had identified a lens that would work, I had the hassle of recalibrating the camera and setting the optical flat field correction for the new lens. I decided against it as a project. I hope you can get it working though.

Have you seen any quotes for a similar custom pure Germanium lens with AR coating yet ? Be warned that they are anything but cheap !

Good luck with your efforts with this camera.


Hi Fraser,

Yeah i saw a few similar specification germanium coated lenses ranging from £130 to £170 from a few suppliers, hoping to get something in between.
Frankly i'm not too bothered if it's not exact match as long as it gives me a decent enough image and accuracy.
The camera is actually very useable for PCB inspection as it is and the image is good enough, that front lens seems to just be for further image field widening rather than anything else. I would even get a slightly wider lens as the default 24 degree is a bit narrow.
The focus can still be adjusted both manually and auto even with the front lens missing.
If a cheap and cheerful germanium lens gets me a fully working camera then i'll be happy, considering it’s a decent spec model.
I'll keep you updated with how things go once i found the right lens.


You could first try with a ZnSe lens of 25mm from Ali-Express. These are quite a bit cheaper and would allow you to try the focal length/design before committing to buy a custom made germanium lens...

Yeah I have one of those too but not happy with qua6, I think germanium coated lenses are much superior.
Price wise a ZnSe is £20-30 and germanium is £100+ though so I get your point.


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