Pentax ZX-30 ZX-30 Manual - Page 64

Pentax ZX-30 Manual

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SNOI1V1:13dO 333NVAaV 62 Calculating the flash effective distance according to the camera-to-subject distance. Maximum flash distance = Guide Number ÷ Selected aperture Minimum flash distance = Maximum flash distance ÷ 5* When the distance to the subject is less than 0.7m (2.3ft), the flash cannot be used. If the flash is used within that distance, it causes vignetting in the picture corners, light is distributed unevenly and the picture may be overexposed. * The value 5 used in the formula above was obtained from the built-in flash. The guide number (GN) depends upon the film speed used as shown below. I SO25 • GN5.5 ISO50 • GN7.8 ISO100 • GN11 ISO200 • GN15.6 ISO400 • GN22 If an ISO100 film is used at an aperture of f/2.8, the flash effective distance is obtained as follows: Guide Number (11) f/2.8 = 3.9m 3.9 ÷ 5 = 0.8m Thus, the flash effective distance is from approx. 0.8m to 3.9m. Calculating the aperture according to the camera-to-subject distance Aperture = Guide Number ÷ Camera-to-subject distance If the calculated aperture value is different than an indicated f-stop in the viewfinder, for instance f/3, choose the next smallest aperture indication (f2.8 in this case).

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62
SNOI1V1:13dO
333NVAaV
Calculating
the
flash
effective
distance
according
to
the
camera
-to
-subject
distance.
Maximum
flash
distance
=
Guide
Number
÷
Selected
aperture
Minimum
flash
distance
=
Maximum
flash
distance
÷
5*
When
the
distance
to
the
subject
is
less
than
0.7m
(2.3ft),
the
flash
cannot
be
used.
If
the
flash
is
used
with-
in
that
distance,
it
causes
vignetting
in
the
picture
cor-
ners,
light
is
distributed
unevenly
and
the
picture
may
be
overexposed.
*
The
value
5
used
in
the
formula
above
was
obtained
from
the
built-in
flash.
The
guide
number
(GN)
depends
upon
the
film
speed
used
as
shown
below.
I
SO25
•
GN5.5
ISO200
•
GN15.6
ISO50
•
GN7.8
ISO400
•
GN22
ISO100
•
GN11
If
an
ISO100
film
is
used
at
an
aperture
of
f/2.8,
the
flash
effective
distance
is
obtained
as
follows:
Guide
Number
(11)
f/2.8
=
3.9m
3.9
÷
5
=
0.8m
Thus,
the
flash
effective
distance
is
from
approx.
0.8m
to
3.9m.
Calculating
the
aperture
according
to
the
cam-
era
-to
-subject
distance
Aperture
=
Guide
Number
÷
Camera
-to
-subject
distance
If
the
calculated
aperture
value
is
different
than
an
indi-
cated
f-stop
in
the
viewfinder,
for
instance
f/3,
choose
the
next
smallest
aperture
indication
(f2.8
in
this
case).