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UBASIC/Scripts: Focus Bracketing

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Revision as of 16:14, November 23, 2013 by Waterwingz (Talk | contribs)

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Focus Bracketing v1.1

AUTHOR'S NOTE: This script was written in the very earliest phases/builds of CHDK, before the get_focus and set_focus commands were available.   It will only work for cameras that support manual focus via the buttons on the camera, as it uses those to bracket the focus.

There are much better scripts written for focus-bracketing now. Please refer to those similar and better scripts. While this script should still work as-is, it is a rather poor work-around to using the more efficient set_focus/get_focus commands in focusing scripts. I'd delete this script from the lists here, but it might be handy for a learning example or just for archival reasons.


Written for/on: Powershot S3 IS, CHDK Build 106 Changeset 159, or later, required.

For Powershot A610: change all occurances of click "down" to click "right" and click "up"' to click "left". NOTE: Not sure if this new version with those edits will work on A-series cameras with the new "press" and "release" commands of CHDK Build 106, can someone confirm?

Also works on: (unknown at this time)

I wrote this script because the camera's built-in focus-bracketing was just WAY too limited for my needs. When doing macro-photography you are working with a minuscule DOF most times. It can take up to 20 or more new focal-planes to get all parts of a subject completely in focus. Using programs like CombineZ (excellent freeware) or Helicon Focus (nice costware) you are able to combine the "in-focus" bits from as many frames as you are able to take. Thus, the need for this more advanced focus-bracketing script. A future version may include an exposure-bracketing option for HDR macro-photos. You'd not only get an amazing DOF but also HDR (high-dynamic range) images too. However, with this script just the way it is, if you put your camera into it's own exposure-bracketing mode you can still get 3 different exposures for each shot -- just not with as much exposure latitude as a CHDK script might create for you. Keeping in mind you will get 3X's more shots for each focus-bracketing step. (CHDK is pretty amazing, no? :-) I know of no other cameras on earth that can automatically do what CHDK cameras are now capable of.)

Documentation/Help (save as a small "focus-brkt.txt" file to your /CHDK/SCRIPTS/ folder)


When starting out, make sure your subject's focus distance is not too close to infinity or the nearest focus setting of the camera. Meaning: allow some focus-space for the bracketing steps chosen so it won't bottom-out hitting a focus limit. Set your "Script shoot delay" to 0, 1, or 2 (depending how fast your camera can use this script). Set the number of bracketing steps you desire, keeping in mind that there will be twice this number of shots taken. 5 bracketing steps = 5-near + chosen-focus + 5-far, 11 shots in total. Step sizes of 2, 3, 4, 5, and even 6 work well. Much will depend on what zoom-setting you are using at the time. More zoom (longer lens FL) means more shallow DOF. And the more you zoom-in the more finer focusing steps are available for you to use. i.e. Wide-angle = few manual-focus steps available. Long-zoom (telephoto) = more manual-focus steps available.


Script Code (save as "focus-brkt.bas" to your /CHDK/SCRIPTS/ folder)

rem Author ~Keoeeit~
rem For S-Series cameras
rem May work on others with edits
rem See documentation

@title Focus Bracketing 
@param a Number of +/- steps 
@default a 2
@param b Step size
@default b 3

if a<1 then let a=2
if b<1 then let b=3

print "Preparing..."
press "mf"
for n=1 to a*b
    click "down"
next n

print "Shoot 1 of", a*2+1
shoot
for s=1 to a*2
    for n=1 to b
        click "up"
    next n
    print "Shoot", s+1, "of", a*2+1
    shoot
next s

print "Finalizing..."
for n=1 to a*b
    click "down"
next n
release "mf"

end
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