Why many thermal cameras cut frequency responding on purpose?

[naze]

I remember Flir told me some of it's thermal cameras have filters that block energy out of it's designed range, such as those under 7um or 8um are blocked for LWIR cameras, why do they waste those energy?

[Vipitis]

The sensor substrate is often limited, so is the lens and coating. There is also an atmospheric window. Cameras are band limited for different applications such as optical gas imaging.

[David Hess]

Unless the sensor is cooled and the optics are suitable, the far infrared spectrum will have low signal to noise making it less useful or useless.

Maybe there are arms control requirements on this aspect of performance like for frame rate and resolution but I am not aware of them.

[Max Planck]

I remember Flir told me some of it's thermal cameras have filters that block energy out of it's designed range, such as those under 7um or 8um are blocked for LWIR cameras, why do they waste those energy?

There is one single reason. Impact of humidity contained in the air (see its absorption spectrum).

Max

[bap2703]

Also known as the need to feed distance and humidity to the radiometric model.

[cnxunuo]

Most likely a high pass filter coating at 7/8um, is for solar protection, which is state in many many literature and brochures.

[Max Planck]

Solar filter is a different story related to cooled MWIR cameras.

Max

[Ben321]

I remember Flir told me some of it's thermal cameras have filters that block energy out of it's designed range, such as those under 7um or 8um are blocked for LWIR cameras, why do they waste those energy?

Filtered LWIR cameras are the sun-safe ones. Ones that do not have a long-pass filter can be damaged by the MWIR from the sun, because MWIR wavelengths pass through germanium lenses (though less then LWIR wavelengths do). The temperature of the surface of the sun is about 5500K, and at this temperature MWIR emissions are a couple orders of magnitude stronger than LWIR emissions (more than enough to not only pass through the germanium lens, but also damage the LWIR sensor).