The source code is available from a git repository hosted at Sourceforge. You can check out the current head revision by
>$ git clone http://git.code.sf.net/p/lensfun/code lensfun-code
The build system is based on CMake. Enter the Lensfun folder and create the CMake build directory:
>$ cd lensfun-code/ >$ mkdir cmake_build >$ cd cmake_build/ >$ cmake ../
Beneath many other files this should have created a Makefile that can now be used to compile and install as usual with
>$ make >$ make install
More information about the build system and available options can be found in the README file in the root folder.