ExpoDev's Factors screen allows you to apply one or more exposure factors to the exposure calculation process. The factors that you can choose from include Filters, Bellows Factor (for close-up compensation), and an overall Exposure Adjustment factor.
When choosing a Filter, ExpoDev will show you the list of your managed filters to choose from along with additional information such as the filter factor to be applied.
The Bellows Factor is used to adjust the exposure for the amount of bellows extension used in close-up compositions. You can choose one of three methods: by subject distance (as measured from the lens nodal point, usually the lens board, to the subject), measuring the amount of bellows extension (film plane to lens nodal point), or by a subject magnification factor (with 1.00 representing a 1:1 reproduction ratio). When a selection is made that requires compensation, ExpoDev will calculate and show the necessary Bellows Factor and apply it to the exposure. ExpoDev will apply a Bellows Factor when the compensation amount is 1/6th of a stop or greater.
Note: In subject distance mode, if the distance is less than or equal to the focal length selected it will be physically impossible to focus the lens on that subject and therefore impossible to calculate a bellows factor. In this special case, ExpoDev will state that the subject it too close.
The Exposure Adjustment factor can be used to give an overall adjustment to the exposure. The range is +/- 2.0 stops in 1/3rds of a stop.
Note: It is generally better to use an accurate Film Profile rather than use the exposure adjustment factor.