Nikon F25B Bedienungsanleitung PDF herunterladen (Seite 24)

EXPOSURE

MEASUREMENT-continued

Exposure

Control

The

amount

of

light reaching

the

film plane

is

deter-

mined

by

a

combination

of

the

lens

aperture

and

the

shutter

speed. Since

the

two

are interrelated,

different

combinations

will give

the

same exposure. A 1-step

change

in

the

shutter

speed,

or

a 1-stop change

in

the

aperture

setting, will

either

halve

or

doubl

e

the

exposure.

For

example, a

shutter

speed

of

1/125

second passes

twice as

much

light as a setting

of

1/250

second,

and

only

half as

much

light as a speed

of

1/60

second;

for

an

aperture

setting

of

f/11,

twice as much light as

f/16,

and

half as

much

as

f/8,

is

passed. This

feature

characterizes

the

oJ)eration

throughout

the

available range

of

shutter

speeds

and

aperture

settings. With this

in

mind, it's easy

to

see

that

if a

correct

exposure

for a scene

is

1/125

at

fill,

then

1/60

at

f/16

or

1/250

at

f/8

will be equally

acceptable.

The

best comb ination for

your

needs will

depend

on

the

results desired. Use

fast

shutter

speeds

to

freeze

motion,

or

use slow speeds

to

produce

deliberate and creative

blur. Small

apertures

give greater

depth

of

field, while

large

apertures

restrict sharp focus

to

the

main subject.

The

creative selection

of

both

speeds

and

apertures

will

greatly

enhance

your

photography.

24

Metering Range

If

the

center

"correct

exposure"

LED fails

to

illuminate,

even

after

all possible lens

-a

perture/shutter

-s

peed com-

binations have been tried,

then

the

available light

is

too

bright

or

too

dim

for

the

meter's

range.

To

correct

this

situation, several measures m

ay

be

taken, as follows:

Switch

to

a new film (either higher

or

lower ASA)

that

more closely

matches

the

available light;

mount

a neutral

density filter on

the

lens

to

decrease

the

light reaching

the

film plane;

or

use artificial lighting (i.e

.,

an electronic

flash unit)

to

increase subject illumination.

Remember

,

too,

that

the

lens

in

use can greatly influence suitability

for bright

or

dim shooting.

For

example, a

50mm

f/1.4

lens (with ASA

100

film) couples from EV - 2

(f/1.4

at

8 seconds)

to

EV

17

(f/8

at

1/2000

second) for excel-

lent low-light

performance;

on

the

other

hand, a

200mm

f/4

lens proves more usable

at

bright-light levels, coupl-

ing (with ASA

100

film) from EV 1

(f/4

at

8 seconds)

to

EV 20

(f/22

at

1/2000).

Thus, choose

the

lens carefully

to

match

the

existing lighting conditions.

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