Bellows extension exposure compensation
Compiled by Q.-Tuan Luong for the Large Format Page
Formulas
Michael Gudzinowicz: ...
4.) BELLOWS EXTENSION FACTORS
As you rack out a lens to focus closer, the light has to travel further from lens to film. F/stop is the focal length divided by the opening of the lens. The opening of a 150mm lens at f/16 is 9.4mm. (150 / 9.
Bellows Extension: When photographing at normal distances you don't need to make any exposure corrections. When you get closer to your subject, you need to compensate for light loss due to bellows extension.
Long bellows extension is also necessary if you want to use lenses of long focal length that are not a telephoto design.
BELLOWS EXTENSION.-A copy camera should be capable of a bellows extension of at least two, and preferably three times or more the focal length of the lens being used.
A bellows comes with a distinct advantage over extension tubes: You can vary macro distance simply by increasing or decreasing the bellows extension, without relying on specific levels of maganification.
safe-keeping of the focusing screen from moisture and dirt
lens board allowing vertical shifts
bellows extension at least double as long as the longest side of the maximum image format
usabilty also with short bellows extension and wide angle lens ...
At the lower magnification range this may not always yield the magnification desired so it may be necessary to retract the lens the necessary amount in combination with bellows extension to achieve the desired magnification.
Different types of specialty lenses.
Extension rings and their uses.
Filters.
How to care for your lenses and camera body.
Bellows extension and filter factor explained.
How to pick the right lens for the job.
 See also: Back, Extension, Image, Bellows, Camera
  
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