I am working on some research on the Kinect for XBOX One. I am looking into the depth measurements of the device. I have read that the depth values are calculated from the devices focal plane. So i had to determine the exact position of the focal plane within the device. I did camera calibration to determine the devices focal length.
The thing i am confused about is the use of the term focal length. In some sources (http://www.sony.net/Products/di/en-us/Learnmore/knowledge/01.html) it is directly used as the distance between the lens and the image sensor and they also say that the image sensor is located at the focal plane. In other sources (http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/image.html) that are more physics focused the make a distinction between the focal length and the image distance.
I asked my advisor at the university and he said i could use the calculated focal length as distance to the image sensor and said that in fixed-focus cameras the image sensor is located at the focal length but could not really explain why.
So my question is can i use the focal length i got from the camera calibration as the distance from the lens to the image sensor or would that be wrong?
I am new here and hope that did this correctly and would be glad for all feedback!