Polaroid mod?

Hello All,
I have an old barrel lens that I want to use in a polariod 4x5 mod that i am about to start. I am wondering what the focal length of a 12cm lens is at infinity? Any help would be greatly appreciated.

Arthur, NYC

The focal length is measured at infinity so a 12cm lens has a focal length of 12cm. That 120mm is from the nodal point of the lens to the film plane which if the lens is symmetrical means the middle of the cells where the f stop iris is.

Ian