The bellows in a large format camera are the accordioon like, expandable part. When focusing the bellows can go further apart meaning there is further light to travel before reaching the negative, to make up for this the exposure needs altering. This is needed mainly in close up photography.
Bellows Extension is when you are compensating for exposure. F/stop is the focal length divided by the opening of the lens. For example 150mm lens at f/16 is 9.4mm.
Bellows Extension²
Focal Length of lens²
Example:
bellows - 30cm-300mm.
300mm²
150mm² = 90,000
22,500 = 4
Every factor is worth half a stop, so in this case a longer exposure is needed by 2 stops to make up for bellows extension.
1 factor = 1/2 stop
2 factor = 1 stop
3 factor = 1 1/2 stops
4 factor = 2 stops
5 factor = 2 1/2 stops.
Reciprocity:
Reciprocity is the inverse relationship between the intensity and duration of that that determines the photograph that comes out. It is used for either very long exposures or very short exposures. This used to be known as Bunsen-Roscoe reciprocity, created by Robert Bunsen and Henry Roscoe in 1862. It is that an increase of brightness by a certain amount can be balanced out by a decrease of exposure time by that same amount.
Zone System:
The zone system gives you control of your negative, giving correct exposure and details. It was created by Ansel Adams and Fred Archer, to help with film exposure and development. There are two stops between each zone.
The way its works is that the blacks are the shadows and whites are the highlights, with 5 being mid grey the colour the lightmeter reads.
First hint of shadow is zone II
Full shadow is zone III
Full highlight is zone VII
Lightest highlight is zone VIII.
Exposure: focusing on the shadows.
To achieve the correct exposure, you use a reflective lightmeter reading. You take 3 meter readings. Taking a reading of the shadow area, the mid grey area, and the highlights area, and determine which zones they would be in. Focusing on the mid grey reading, you would then underexpose by 2 stops to get the correct the shadows correctly exposed.
Development: focusing on highlights.
You can alter the development by changing the timing.
N - normal
N+1 - add 1 and 1/2 minutes (keeps shadows the same, but changes the highlights)
N-1 - takes away a minute.