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root/radiance/ray/doc/notes/filmspeed
Revision: 1.1
Committed: Sat Mar 15 17:32:55 2003 UTC (21 years ago) by greg
Branch: MAIN
CVS Tags: rad5R4, rad5R2, rad4R2P2, rad5R0, rad5R1, rad3R7P2, rad3R7P1, rad4R2, rad4R1, rad4R0, rad3R5, rad3R6, rad3R6P1, rad3R8, rad3R9, rad4R2P1, rad5R3, HEAD
Log Message:
Added and updated documentation for 3.5 release

File Contents

# Content
1 Francis found the appropriate equation for film exposure in the IES
2 handbook. There isn't an exact relation, but the following formula
3 can be used to get an approximate answer for 35mm photography:
4
5 Radiance EXPOSURE = K * T * S / f^2
6
7 where:
8 T = exposure time (in seconds)
9 S = film speed (ISO ASA)
10 f = f-stop
11 K = 2.81 (conversion factor 179*PI/200)
12
13 This came from the IES Lighting Handbook, 1987 Application Volume, section 11,
14 page 24.
15
16 So, if you were trying to produce an image as it would appear shot at
17 1/60 sec. on ISO ASA 100 (DIN 21) film at f-4, you would apply pfilt
18 thusly:
19
20 pfilt -1 -e `ev "2.81*1/60*100/4^2"` raw.pic > fin.pic