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The working wavelength of Optotherm LWIR thermal cameras is typically between 7 - 14 microns, with the center wavelength at approximately 10 microns. And for object temperatures between 0 and 100°C, peak emittance is close to 10 µm.

The spatial resolution that can be achieved using a LWIR lens is limited by diffraction, which provides a practical limit of approximately 1/2 the working wavelength according to spatial resolution calculations such as the Rayleigh criterion.

LWIR Diffraction Limit = 0.5 * 10 µm = 5 µm.

This is the primary reason we developed the 5µm lens for the IS640-17 thermal camera as it provides the smallest spatial resolution achievable (each 5 x 5 µm area on the target is imaged onto each sensor pixel element). Due to diffraction effects, there is slight overlap of energy on adjacent sensor pixel elements.  Magnification beyond this level only results in significant blur over adjacent sensor elements and very low working f/#, reducing measurement sensitivity significantly.

If smaller spatial resolution is required, consider the Optotherm MW640-15 cryogenically cooled MWIR camera with 2µm lens.