Here is a list of all related documentation pages:

Software license
Credits
Build instructions
Updating Lensfun's database: lensfun‑update-data
Adding mount adapters: lensfun‑add‑adapter
Converting Adobe LCP files to Lensfun: lensfun‑convert‑lcp
Lens database
Database file format
Database format versions
Describing camera mounts: <mount>
Declaring cameras: <camera>
Declaring lenses: <lens>
Lens calibration data format
How database files are found and loaded
How the corrections work
Applying perspective correction
Using this library in your programs
Library architecture
Filling the database
Adding new cameras to the database
Adding new lenses to the database
Sample code
GNU General Public License, version 3
GNU Lesser General Public License, version 3
Creative Commons Attribution-Share Alike 3.0 Unported