Viewing Through a Window

Particularly common with high heat applications, sometimes we must view through a window, glass, viewing pane.

There are just a few things to keep in mind when doing this:

1. Keep the window as planar to the sensor planes as possible.  Sometimes the cameras are each in its own enclosure.  This is great because the window is planar to the sensor.  Also, with Vic-2D this is typically not an issue because the window will be planar to the sensor.  However, if we are viewing through a single glass window with a stereo system, it's impossible for both the sensors to be planar to the window.  As long as the stereo angle is low, the distortions introduced by the window are minimal.  If you can keep the stereo angle between the cameras a maximum of 20 degrees, this would be ideal.  Keep in mind your lens selection parameters.  With a stereo angle of 20 degrees, you should be working with lenses that are 35mm or longer.
Lens Selection and Stereo Angle

2. There are a couple ways to calibrate through the glass window.  You can calibrate through the actual window (calibrate with glass window in place, so you are viewing through the window, as you do during a test).  But what is actually preferred is that you calibrate with NO glass window in place and then use the External Orientation Calibration with the window in place in order to "Correct" the calibration for the window.  For more on this feature, click here:
External Orientation Calibration

3. With thermal tests, keep in mind that heatwaves can result in huge false strains and noise.  There are several ways to help avoid this.  Using multiple layers of window panes, allowing the test to come to thermal equillibrium, moving the air between the sample and cameras (with a fan), and if the test is static enough you can take several images at each instance and the use our Time Averaging feature in post processing to remove some of the noise.  If you have a heat test, you WILL have heat waves, unless you take the measures above to help remove them.  Click here for more on heatwaves in DIC:
Heat Waves in DIC

4. Keep the glass window as clean as possible.  The more optically clear the glass is, the better results you will have.