How Bellows Extension compensation works
Extra exposure for the light loss when the bellows racks out.
Where to find it
Tools tab Bellows Extension
Summary
Calculator for view-camera bellows extension exposure compensation. When the lens racks out for close focus, light has further to travel and the image dims; this modal works out exactly how much extra exposure to add.
Detail
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How it works
When you focus close on a view camera, the bellows racks the lens away from the film. Light has to travel further, and the further it travels, the dimmer it gets. This modal works out how much extra exposure that costs you so the image is not silently underexposed.
Bellows draw
The distance from the lens diaphragm to the film plane. At infinity focus this equals the focal length. As you focus closer, it gets longer. Some cameras have a tape on the bed; otherwise measure with a ruler.
Focal length
Pulled from your selected lens. The compensation depends on the ratio of bellows draw to focal length, so a long lens needs less compensation for the same magnification than a short lens does.
How much extra
At 1:1 magnification (life size on the negative) you need plus two stops. At 1:2 magnification it is plus one stop. The modal shows the exact stops to add to your metered exposure.
When you do not need it
Modern SLRs with internal metering already see through the lens, so the meter automatically accounts for bellows. This modal is for view cameras and any rig where you meter externally.