Hi @Jianxin xiao Thank you for posting the question here.
Azure Kinect DK device lets you operate in the following two modes.
Depth camera mode uses ToF sensor which has a focal length of ~1.8mm. Color camera mode operates using RGB sensor which has a focal length of ~2.3mm.
A similar question has been posted on the forum in the past which can be accessed through the following link for additional information - Pixel size of RGB and TOF camera
Hope this answers your question. Let us know if you need any additional information.
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