ASAHI PENTAX Z-70 Operating Manual page 72

змоцмнздо азомулам ІП
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), flash cannot be used. If the flash is used within
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 numbers (GN) depend upon the film speed
used as shown below.
Guide Number (13) = £/2.8 = 4.6m
46 + 5 = 0.92m
Thus, the flash effective distance is from approx. 0.92m
to 4.6m.
Calculating the aperture according to the camera-to-
subject distance
Aperture = Guide Number + Camera-to-subject dis-
tance
If the calculated aperture value is the one other than an
f-stop on the aperture ring, for instance 1.3. choose
the next smallest aperture ring (f2.8 in this case).
Built-in Flash effective range for Programmed TTL.
Auto Flash with ISO 400 film used
6025 — GNes |
5050 — GN92
150200 ~ GN18
150400 — GN26
150100 -- GN13
If an 150100 film is in used at an aperture of #2.8, the
flash effective distance is obtained as follows:
68
Maximum Lens Aperture Effective Range
1/14 approx. 0.9 - 6.5m (3.0 - 21.350)
1/2 approx. 0.8 - 5.8m (2.6 - 19.0ft)
1728 approx. 0.7 - 4.6m (2.3 - 15.19)
173.54747 approx. 0.7 - 4.6m (2.3 - 15.19)
£756 approx. 0.7 - 4.6m (2.3 - 15.1ft)