Hasselblad H2F Uživatelský manuál stáhnout pdf (Strana 78)

True exposure

e eective shutter speed for a central lens shutter is dened as

the length of time between the opening and closing when measured

at the half height position when expressed in diagram form (see

diagram). e fact that it will take some time to open and close

the shutter will have an inuence on the eective shutter speed as

the lens aperture closes to its setting. e faster the shutter opens

and closes, the less this inuence will be. It is also follows that the

inuence will be greater on shorter shutter speeds.

With the lens at full aperture (largest opening), the amount of

light at the lm plane appears as illustrated by the blue curve in

the diagram. e eective shutter speed then becomes T1. If the

lens is now closed down by one stop, the amount of light appears

as illustrated by the red dashed curve. e eective shutter speed

is now increased to T2, which is longer that T1. e result is that

the exposure is not reduced by exactly one stop (1EV), however,

but slightly less. At the shorter shutter speeds, the exposure error

can be as much as 0,5 – 0,8 EV.

e True exposure mode can compensate for this exposure error

since the behaviour of the shutter is a known and predictable factor.

At shutter speeds of 1/150 second or shorter (faster), the camera

will shorten the shutter speed to compensate, as illustrated by

the green dashed curve. At the fastest shutter speeds, however, it

is not possible to adjust the shutter speed and so the aperture is

adjusted instead.

Although it is probably an infrequently used combination, please

note nevertheless that the fastest shutter speed / minimum aperture

combination cannot be adjusted by True exposure.

= T

Shutter position

Time

Open

Closed

Exposure at max aperture (e.g. f/2,8)

Exposure at aperture f/4

Exposure at aperture f/4 adjusted with true exposure

Shutter position

Open

Closed

Time

Exposure at max aperture (e.g. f/2.8)

Exposure at aperture f/4

Exposure at aperture f/4 adjusted with true exposure

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Hasselblad H2F Uživatelský manuál Strana 78