Electrophysics offers a complete line of high-performance infrared cameras, thermal imaging and night vision cameras. Our products include: image intensifier, IR thermal imaging, low light products and more.
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Spot Size Ratio Guidelines
 
Guidelines
 

1. This calculator is not meant to describe a rigorous approach for determining measurement spot size. It merely describes a method by which a user can estimate either the minimum object size measurable with a certain infrared camera at a specified distance or to estimate the maximum distance that a specified object size can be measured.
 
2. When selecting a camera, keep in mind that IFOV is a good figure of merit to use. The smaller the IFOV, the better the camera for a given total FOV.
 
3. For some infrared cameras in certain circumstances, the measurement spot size may vary for different positions on the display. In general, the best measurement spot size is achieved in the center of the field of view.
 
4. The Camera Parameters "Horizontal Field-of-View" and "Detector Array Size (horizontal)" are specifications that are readily available on a camera specification sheet or operating manual. "Effective pixels/spot" is a characteristic that is unique to each individual infrared camera and is used here for convenience to estimate the camera measurement modulation transfer function (MTF) performance. Cameras with fewer "Effective pixels/spot" perform better at measuring small objects at a distance. In general, this number cannot be less than 1 for non-dithered detectors and will not be more than 10 for even the lowest performance camera. If you are uncertain about a value to use, experimentation should be used to estimate it (whereby a known small object is measured at different distances and a value is determined that corresponds to the limiting measurement distance).
 
5. For the sake of simplicity, it is assumed that measurement spot areas are circles. This is usually a good estimation since infrared cameras normally use pixels that are square and arrays with equal horizontal and vertical pixel pitch.
 
6. Spot Size Ratio (or SSR) is given by the formula: SSR = distance to object/measurement spot size. The higher the number the better since it means that small objects can be resolved at relatively large distances. SSR is not just to make estimates for objects that are far away. It can also be used to estimate sizes for close-up inspection. In these circumstances, the camera's minimum focus distance must also be considered. For shorter target distances, some manufacturers offer close-up lenses.
 
DISCLAIMER: We have made every attempt to provide accurate information. However, we cannot accept any responsibility for errors or inaccuracies. Should you identify errors or require assistance, please contact us directly. Thank you.
 
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