Thermal Imaging Lenses

  • Lenses for Thermal Imaging Cameras
  • Focus Infrared Light without Introducing Spherical Aberration
  • Horizontal Field of View (FOV) Options from 18° to 56°


4.0 mm Focal Length


7.7 mm Focal Length


15 mm Focal Length


20 mm Focal Length


24 mm Focal Length

Related Items

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Common Specifications
Lens Substrate Black Diamond-6a
AR Coating Range 8 - 12 µm
Reflectance over Coating Range (Avg.)b <0.75% at 0° AOI
AR Coating Reflectance
(Click Icon for Plot)
(Click Icon for Plot)
Substrate Properties
Refractive Index 2.7867 at 8 µmc
Coefficient of
Thermal Expansion
22.5 x 10-6 / °C
Thermooptic Coefficient (Δn / ΔT) 30.5 x 10-6 / °C
  • Click link for detailed specifications on the substrate.
  • Per Surface.
  • See the Refractive Index tab for the wavelength-dependent refractive index.
Zemax Files
Click on the red Document icon next to the item numbers below to access the Zemax file download. Our entire Zemax Catalog is also available.
Webpage Features
info icon Clicking this info icon below will open a window that contains specifications, a reference drawing, and horizontal field of views for various detector sizes.


  • Focus Infrared Light without Introducing Spherical Aberration
  • 8 - 12 µm AR Coating for Long-Wave Infrared (LWIR) Applications
  • Black Diamond Substrate Provides Stable Operation up to 110 °C
  • Horizontal Field of View (FOV) Options from 18° to 56°
  • Focal Lengths of 4.0 to 24 mm Available
  • Mounted in Threaded, Engraved Black Anodized Aluminum Housings
  • Internally Sealed to IP67 Standard

Thorlabs offers Thermal Imaging Lenses that are ideal for focusing long-wave infrared (LWIR) sources onto detectors or image sensors. The lenses, manufactured by LightPath Technologies, are mounted in threaded, black anodized aluminum housings engraved with the focal length and f/# (see the table below for details). Designed using Black Diamond-6 glass, their aspheric geometry allows them to focus light without introducing spherical aberration. The TIL4 and TIL8 lenses feature singlet designs, while the TIL15, TIL20, and TIL24 are doublets.

Black Diamond
Black Diamond-6 (BD-6), a chalcogenide made of an amorphous mixture of arsenic (40%) and selenium (60%), has several advantages over germanium, which is traditionally used to fabricate IR optics. BD-6's thermally stable refractive index (see the Refractive Index tab) and low coefficient of thermal expansion (22.5 x 10-6 / °C) result in a smaller change in focal length as a function of temperature than for germanium. Additionally, germanium suffers from transmission loss as temperature increases, while BD-6 aspheric lenses can be used in environments up to 110 °C. This material performs particularly well over the 2 - 12 µm spectral range (click here for the transmission of an uncoated 1 mm thick sample).

Item # Info EFLa WDb HFOVc VFOVc Ideal Detector Formatd Surface Quality Aperture Height f/#e Design Thread
TIL4 info 4.0 mm 5.33 mm 56° 42° 320 x 240 / 12 µm 80-60 Scratch-Dig Ø3.33 mm 6.50 mm 1.2 Singlet M10 x 0.5 - 6g
TIL8 info 7.7 mm 10.06 mm 41° 31° 320 x 240 / 17 µm 100-60 Scratch-Dig Ø5.80 mm 11.50 mm 1.3 Singlet M19 x 0.5 - 6g
TIL15 info 15 mm 10.07 mm 25° 18° 640 x 480 / 10 µm 80-50 Scratch-Dig Ø12.46 mm 17.00 mm 1.2 Doublet M19 x 0.5 - 6g
TIL20 info 20 mm 7.96 mm 18° 14° 640 x 480 / 10 µm 80-50 Scratch-Dig Ø16.60 mm 21.42 mm 1.2 Doublet M19 x 0.5 - 6g
TIL24 info 24 mm 10.00 mm 26° 19° 640 x 480 / 17 µm 100-60 Scratch-Dig Ø19.90 mm 26.50 mm 1.2 Doublet M25 x 0.5 - 6g
  • EFL is magnification-based.
  • Assumes 0.76 mm Si Window, Nominal Focus at Infinity
  • Given for Ideal Detector Format
  • Given in Resolution (H x V) / Pixel Size
  • Obtained by dividing the effective focal length of the lens by its aperture.

EFL = Effective Focal Length
WD = Working Distance

HFOV = Horizontal Field of View
VFOV = Vertical Field of View

A 2.787
B 1.194 x 10-1
C 1.760 x 10-2
D -1.161 x 10-4
E -3.870 x 10-8
F -6.037 x 10-11

The refractive index, n, of Black Diamond-6 (BD-6) as a function of wavelength, shown above, was calculated using the Herzberger Equation, an infrared-specific analog of the Sellmeier Equation. The Herzberger coefficients for BD-6 are given in the table to the right.

Herzberger Equation (for λ in µm)

Herzberger Equation

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Lightpath Thermal Imaging Lenses

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+1 Qty Docs Part Number - Universal Price Available
TIL4 Support Documentation
TIL4Lightpath Thermal Imaging Lens Assembly, 4.0 mm Focal Length, f/1.2, M10 x 0.5
TIL8 Support Documentation
TIL8Lightpath Thermal Imaging Lens Assembly, 7.7 mm Focal Length, f/1.3, M19 x 0.5
TIL15 Support Documentation
TIL15Lightpath Thermal Imaging Lens Assembly, 15 mm Focal Length, f/1.2, M19 x 0.5
TIL20 Support Documentation
TIL20Lightpath Thermal Imaging Lens Assembly, 20 mm Focal Length, f/1.2, M19 x 0.5
TIL24 Support Documentation
TIL24Lightpath Thermal Imaging Lens Assembly, 24 mm Focal Length, f/1.2, M25 x 0.5