Hugin Exposure tab
TODO explain why there is an Exposure tab.
Camera and Lens variables
The Camera and Lens variables are the photometric analog of the geometric lens correction model, hugin assumes that all input photos with the same lens number have identical values unless they are unlinked in the hugin Camera and Lens tab.
Vignetting is dependent mainly on your lens and the aperture. Usually the centre of the image is brighter with a falloff towards the edges, hugin can calculate this falloff curve as part of the photometric optimisation process or you can enter it manually here as three numbers.