This calculator is a quick and easy way to calculate the exposure adjustment for bellows extension in the field. When shooting cameras that use bellows, an EV adjustment must be added to the metered light reading to account for light lost from extending the bellows to focus. This calculator allows the user to enter the amount of bellows extension and lens focal length values, and outputs a simple, easy to read, EV adjustment. No need need to carry around complicated formulas, scratch pads, or scientific calculators in the field.