FINAL VERSION OF THE SCRIPT
(and instructions)
This script attempts is meant to shoot time-lapse videos of sunsets: starting from full daylight and ending in full night, always adapting exposure for a correct shot.
Up to a certain point (when there is enough light to be directly measured) the script exposes automatically, then starts guessing the exposure, increasing first exposure time (up to a certain limit) then ISO (again, up to a certain limit).
Suggested camera settings:Camera mode: manual
White balance: Sun (other settings, if desired but
not auto)
Image size: a small image size (S) is suggested, in order to allow more shots
Flash: off
Focus: manual, set to infinity
Aperture: maximum
Note: all the parameters here are expressed in APEX*96 units, with equivalence.
First, you wll have to decide the delay between one shot and the other (how many seconds between each shot)
Suggested values: 5 or 10 seconds. Longer might also be ok, bu the resulting video will be shorter.
Then, you will have to decide what will be the final exposure parameters. These will depend strongly on the type of scene you will be shooting.
Examples of suggested values:
Landscape with strong lights (city), illuminated sky 5" (Tv -224) ISO 1250 (Sv 767). Stars will be barely visible
Landscape without lights (countryside), dark sky 15" (Tv -384) ISO 2500 (Sv 864) Stars will be well visible
These parameters are called "Limit Tv" and "Limit Sv" in the script.
Finally, you have to decide the "Default Sv", (the ISO settings to start with). I suggest ISO 100 (Sv 419)
Other values ("Guess mode limit" and "Slope in guess mode") are better left to their default values
You can now run the script.
For debugging purposes, the program logs quite some information in the PR_SCREEN.TXT file (in CHDK/SCRIPTS). If you have problems with the script, save the PR_SCREEN.TXT so that problems are better pinpointed.
This is the script:
@title Sunset4
rem Script to shoot time-lapse videos of sunsets
rem v. 4, Fbonomi apr 30th 2008
rem Released under GPL
@param a Delay (sec)
@default a 10
@param b Limit Tv
@default b -414
rem (-414=20 sec; -384=15 sec; -320=10 sec; -224=5 sec.)
@param c Default Sv
@default c 480
rem (480=160)
@param d Limit Sv
@default d 776
rem (776=1250 ISO; 960=5000)
@param e Guess mode limit
@default e -200
@param f Slope in guess mode
@default f 5
print_screen 1
print "Sunset Time Lapse"
rem initialize guess mode value
x=e
rem get start Tv
get_tv96 T
rem picture counter
p=1
:loop
rem measure luminance and aperture
press "shoot_half"
sleep 500
release "shoot_half"
get_bv96 B
get_av96 A
rem release "shoot_half"
print "Measured: ",B ,A
rem resulting Tv would be:
T=B-A
T=T+c
print "Calculated T: ", T
rem check Tv Values
if T>e then
rem normal mode, shoot with calculated Tv and default Sc
X=T
Y=c
print "Mode: Standard"
else
rem Guess mode, every shot will be 5/96th steps longer
x=x-f
if x>b then
rem we are in dark, but exposure is not too long
rem normal mode, shoot with guessed Tv and default Sc
X=x
Y=c
print "Mode: Guess"
else
rem we are in very dark area, we want to avoid too long exposures
rem shoot with maximum allowed time (b) and
rem adjust Sv accordingly
X=b
Y=c+b-x
rem BUT check we don't go in too high ISO!
if Y>d then
Y=d
endif
print "Mode: Guess with High ISO"
endif
endif
rem we can now shoot
sleep 100
set_sv96 Y
set_tv96_direct X
sleep 100
shoot
sleep 100
print "SHOOT ",p,X,Y
p=p+1
sleep a*1000
goto "loop"
