JEITA CP-3451
- 122 -
Annex C
APEX Units
The camera information in this standard conforms to the APEX (Additive System of Photographic Exposure) unit
system. APEX is a convenient unit for expressing exposure (Ev). The relation of APEX to other units is essentially
as follows.
b) ApertureValue (Av) = 2 log 2 (F number)
c) ShutterSpeedValue (Tv) = - log 2 (exposure time)
d) BrightnessValue (Bv) = log2 ( B/NK )Note that: B:cd/cm2, N,K: constant
Film sensitivity (not used in this standard) is expressed as follows.
e)
Film sensitivity (Sv) = log2 ( ASA / 3.125 )
Using these values, exposure (Ev) is calculated as follows.
f) Ev = Av + Tv = Bv + Sv
The table below gives examples of values actually used as camera information.
Table 48 Typical APEX Values
ApertureValue
F-Number
ShutterSpeed
Value
ExposureTime
BrightnessValue
foot lambert
(APEX)
(APEX)
(second)
(APEX)
0
1
-5
30
-2
1/4
1
1.4
-4
15
-1
1/2
2
2
-3
8
0
1
3
2.8
-2
4
1
2
4
4
-1
2
2
4
5
5.6
0
1
3
8
6
8
1
1/2
4
15
7
11
2
1/4
5
30
8
16
3
1/8
9
22
4
1/15
10
32
5
1/30
6
1/60
7
1/125
8
1/250
9
1/500
10
1/1000
11
1/2000
