For those interested in IR transparent materials there is plenty of information on the NET detailing how different materials behave at the various wavelengths used in thermal imaging. I attach a simple table of materials that may be used in lenses and a link to another version that clearly shows the three different wavelengths used in the industry, Short, Medium and Long wave. The E4 is a long Wave thermal camera. Some material, such as silicon are not well suited to Long wave lens structures yet work fine at shortwave
http://www.infraredtraininginstitute.com/infrared-transparent-materials/There are similar tables for thin plastic but I have not tracked them down yet. I will add them if/when I do.
Dave's experiments have been good at demonstrating how materials behave in these areas of the EM spectrum.
Something that is also worthy of experimentation is emissivity. This can have a really dramatic effect on any temperature readings. As an example, a nice shiny aluminium heat sink can be running at +80 Degrees Celcius yet the thermal camera can misread it due to emissivity error and show it at ambient ! The emissivity setting in the camera should be set to the value of the target item to achieve the most accurate measurement. Life is never that simple though....how do you know the true emissivity of a target surface ? That's a whole other story that I will not go into here. Some people may think that to solve the emissivity problem, just paint the target matt black..... well they are on the right path but readers should be aware that where paint in concerned, colour often makes no difference at thermal wavelengths in terms of emissivity. Silver paint and paint loaded with metals may behave differently (worse) to a nice matt paint but basically you will still not have a perfect emissivity in either case. To achieve 'Black body' levels of emissivity (1.00) a very special paint coating is needed that radiates the heat far more efficiently than any generic paint. It may also be interesting to know that the soot from a candle is a very good coating where good emissivity is required. Also a common material used as a quick and dirty emissivity enhancer is everyday standard PVC insulation tape. Colour is NOT critical
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/xwink.gif.pagespeed.ic.cldandycH0.png)
A shiny metal surface with low emissivity may be easily measured with a TIC once a piece of PVC insulation tape is applied. From memory the emissivity of PVC insulation tape is 0.96 to 0.97.
Readers should also be aware of the issues created by reflections. If a thermal camera is brought into close proximity of an object that has reflective thermal properties, it is possible to actually skew the measurements as the camera actually starts to see itself reflected in the target and the E4 has a core running at around +30 degrees C that emits through the lens and may be reflected back at the camera. To see an extreme case of this, point the E4 at a mirror or glass and you will see a selfie
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)
The lens will look warmer than the case....you are seeing the reflected core temperature.
Cryo-cooled cameras project a cold image from the 70K core through the lens that has the opposite effect on readings. These effects are most apparent when working in a close-up configuration with variable target materials. There are plenty of traps for the newbie thermographer
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/xwink.gif.pagespeed.ic.cldandycH0.png)
All this is drifting off topic I know, but I just wanted to highlight that there are some very interesting experiments that may be carried out using a thermal camera. Hours of fun on a wet day if you are bored
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/xgrin.gif.pagespeed.ic.QVVz6XIT20.png)
Oh and nit picker time..... the Ex series cameras do not use a Germanium lens as stated in the videos. Chalcogenide glass is the material used in these and many other 'budget' thermal cameras as it is far cheaper than Germanium in terms of production costs. Germanium crystals are cut to shape with a single diamond tool, Chalcogenide glass may be moulded.
http://www.lightpath.com/infrared-optics/thermal-imaging-assemblies.html