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 Posted: May 24, 2012 - 07:37 PM |
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Joined: Feb 19, 2003
Posts: 2233
Location: Seattle, WA
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We are looking at purchasing a thermal imaging camera at work. I'm trying to choose one. A vendor is telling me that I must get the Flir E40 along with the 45 degree close up lens. They are saying that I can see objects that are 125 microns wide with this setup. My math suggests that I can see objects that are 1mm wide. (and 8x difference!)
But I'm no optics guy.
The specs for the lens are:
Field of view (FOV): 45° × 33.8°
Minimum focus distance: 0.20 m (0.66 ft.)
Focal length: 9.66 mm (0.38 in.)
Spatial resolution (IFOV): 3.93 mrad/2.45 mrad
F-number: 1.3
The sensor's resolution is 160x120. So, to get the mimimum pixel size, I do this:
(Image width/2) / focus distance = tan(FOV/2)
Spot size = image width/resolution
Spot size = tan (FOV/2) * focus distance * 2 / resolution
= tan (45/2) * 0.2m * 2 / 160 pixel
= 01.03mm/pixel (not 0.125mm/pixel)
Am I messing something up here?
Thanks!! |
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Posted: May 24, 2012 - 11:14 PM |
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Joined: Jun 15, 2008
Posts: 1757
Location: North Carolina USA
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My eyes glaze over with those numbers at the moment, but seeing objects x microns wide does not require x/2 micron resolution. If an object scatters enough it will introduce enough contrast to say there is something there to the nearest pixel.
The resolution becomes involved when you want to know how far apart are two objects such as points or lines. It is customarily based on a 20% dip in contrast between the two, although three sigma S/N contrast can be much smaller than that.
Drill down in the specs to the resolution or point spread function. |
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