I recently purchased a Seek RevealPro Thermal Camera, which boasts a 320 x 240 thermal sensor with >15 Hz frame rate at an incredibly affordable price.
One of the only issues that I have with this camera is that it comes with a fixed 32° field-of-view lens. This is OK for general thermal inspection, but it’s a real disadvantage when trying to use the camera for close-up work to assess dissipation on printed circuit boards, or for identifying a faulty or undersized component. On the opposite side of the distance range, the 32° FOV lens makes it difficult to see and measure the temperature of objects at a distance, or of smaller objects at normal distances.
I thus decided to build magnifying (“macro”) and close-up (“telephoto”) converters for the RevealPro. I’m passing along information on my designs in hopes that others will find it useful. You can read detailed instructions in the following whitepaper: Diy-Thermal-Camera-Telephoto-Converter
Macro Lens Converter
The paper describes how a simple Ge or ZnSe plano-convex lens allows the camera to be placed much closer to the object under examination, providing magnification that is inversely proportional to the lens’ focal length. The upper-left pane of the figure shows the heatsink vents of my laptop as imaged by the Seek RevealPRO’s fixed lens. The fixed focus of the RevealPRO requires a minimum distance of around 6”. Placing plano-convex lenses of decreasing focal lens in front of the camera allows larger and larger magnifications of the image, revealing details that are completely lost with the unaided camera:
Telephoto Lens Converter
Imaging an object at a distance with a thermal camera requires a simple telescope made with lenses that work in the 10 µm range. A basic refracting telescope that has two optical elements, an objective and an eyepiece. The objective is a large lens that collects light from a distant object and creates an image of that object in the focal plane. The eyepiece is just a magnifying glass through which the thermal camera can view the virtual image. The paper provides details about the selection of lenses and design of the telephoto converter.
I’m very pleased with the results. The following figure shows some sample images of the telephoto converter in use. The left panes show the image captured through the Seek RevealPRO’s fixed lens. The right panes show the same scene using the ×3.33 telephoto converter of Figure 9. I added an orange rectangle to the images on the left panes to indicate the region magnified by the telephoto converter. The rectangle’s dimensions are 1/3.33 those of the image frame, demonstrating that the magnification achieved by the telephoto converter is indeed ×3.33.
Download detailed whitepaper: Diy-Thermal-Camera-Telephoto-Converter
Attaching Converter Lenses to the Thermal Camera
Macro and telephoto converters are easily used when hand-held in front of a camera. However, for a more stable solution you may want to consider permanently attaching a Thorlabs SM05NT ($6.58) SM05 Locking Ring (ID 0.535″-40, 0.75” OD) to your camera’s lens mount so that you can quickly mount macro or telephoto converters in front of the camera’s lens without affecting its original functionality.
For my application, I needed the camera and telephoto converter to remain at a fixed location referenced to the device on which I was performing a thermal analysis, so I post-mounted the camera and telephoto converter on a small aluminum optical breadboard as shown in the following figure:
The telephoto converter is also presented as an Instructables project at: https://www.instructables.com/id/Diy-Thermal-Camera-Telephoto-Converter/
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