How to use Tv value - Script Writing - CHDK Forum

# How to use Tv value

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#### shane1800

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##### How to use Tv value
« on: 15 / September / 2011, 16:05:21 »
Hello,

I'm a bit new to this world and am trying to figure out how to make this script to start with around a 20 second exposure or 25 or 35 etc.  I figured out 32 and 64 seconds by playing with the numbers but I really don't understand the variables.

Thanks,
Shane

http://chdk.wikia.com/wiki/UBASIC/Scripts:_Shutter_Speed_Stack_(AllBest_build)

There are 7 parameters that can be set:
a - EV fraction (1/x EV) - specify the EV fraction, used for both Start/End and stepping (e.g. 3 = 1/3EV, 6 = 1/6EV, etc.)
b - Start Tv (1EV) - specify the starting EV in whole EVs (relates directly to shutter speed), 0=1sec, +slower speeds, higher exposure, -higher shutter speeds
c - Start Tv (1/xEV) - specify starting EV fraction (is appended to b to allow partial EV, must be from 0 to a)
d - No.Shots - Number of shots to be taken (>0, can be set to take one shot only)
e - Step Size (y/x EV) - how much to step up/down each exposure for each shot (can be 0 to lock shutter speed)
f - Start Delay (s) - delay to start shooting
g - Delay between shots (s) - delay between consecutive shots
When starting the script, the start and end shutter speeds will be calculated and presented on-screen (only start if 1 shot), the user then hits set to accept or any other key to cancel. The script will then take the shots required. For each shot, the shutter speed will be displayed, as well as the shutter value.
EG:
a =  3
b = -11
c =  2
d =  2
e = -1
2 shots to be taken, step size = -1/3EV (e/a)
start EV = -11 2/3
end EV = -12
Tv Start ~1/3243 s
Tv End ~1/4096 s