Canon Camera Hackers Manual page 190

minIso = 384 -- ISO 50
--[[ Correction values for
high shutter speeds
(unit = 1/96th f-stops).
First value for 1/1000,
second value for 1/2000, etc.
+ too dark, make brighter
- too bright, make darker
]]
corr = {0,0,0,0,0,0,0,0,0,0}
function compute_corr(tv)
if tv >= 960 then
local i1 = idiv(tv-960, 96)
local c1 = corr[i1]
local c2 = corr[i1+1]
return idiv(
(c2-c1)*(tv%96),96) + c1
else
return 0
end
end
All the prerequisites are now set up, and the script execution can begin. The
parameter s is clipped to its limits, and the maximum acceptable Sv96 is
computed. Then the Bv96 value is read by half-pressing the shutter button,
waiting until the camera signals "ready to shoot", and reading out the Bv96
value.
Next, the ND filter is switched out, the Tv96 value is read, and the Av96
value is read, too. This seems to be superfluous for cameras without dia-
phragms, but it isn't: the aperture changes with the focal length. At a tele-
photo setting, the aperture is usually smaller than at wide-angle setting:
if s < 1 then
s = 1
elseif s > 8 then
s = 8
end
maxSv = 288 + s * 96
press("shoot_half")
repeat
sleep(1)
until get_shooting()
5.7 Example scripts
181