One of the more popular uses of scripts and automated camera actions is to use exposure bracketing to make HDR images (combining several differently exposed images to increase the captured dynamic range far beyond what any camera can achieve in a single shot). This used to require some additional and more complex scripting commands, as can be seen by studying the HDR Scripts posted here. However, since the Allbest Build was introduced there has been a simpler way whereby nearly any intervalometer script may be used for this purpose.
All that is required is that your build of CHDK has the "Extra Photo Operations" menu with the "Bracketing in Continuous Mode" feature, and that your camera has a built-in Custom Self-Timer.
- 1. Go to your camera's menu (not CHDK's <ALT> menu), and select the "Self-Timer -> Custom" feature. Press [Menu] to enter the custom timer options menu. Set the "Delay" to 0 (zero) seconds. Set "Shots" to how many bracketed shots that you want for each HDR sequence (usually 3 or 5). Press [SET] to exit your custom timer settings. Press [Menu] again to exit your camera's menu options.
- 2. Go to CHDK's "Extra Photo Operations" menu and select "Bracketing in Continuous Mode". Set the bracketing type desired for HDR (usually Tv bracketing is used but some people use Av bracketing). Set "Bracketing Type" to "+ / -". Press [Menu] to set.
- 3. Enter CHDK's <ALT> menu and run any single-shot intervalometer script, such as Ultra Invervalometer.
Each time the script triggers to take a single shot, your custom-timer mode kicks in and takes as many photos as it was set for. At the same time, the CHDK built-in bracketing mode changes the exposure for each shot. This process repeats for each intervalometer script's single-shot command.
This may seem confusing at first but once you understand what is going on it becomes a simple process to remember. The script controls how often to take a bracketed sequence. The camera's custom-timer mode sets how many bracketing shots to take, and the CHDK bracketing mode determines the EV range and type of bracketing for each shot.
The upside of knowing this is that you no longer need a gazillion little scripts to do each type of bracketing sequence. Only one decent intervalometer script is needed to do all manner of bracketing shots. The bracketed shots are taken at a high-speed so there will be little change between bracketed shots when it comes time to stack them. An intervalometer script may even be turned into an elaborate focus-bracketing script using this method -- a huge bonus for intervalometer macro-photography where you might need an extremely deep depth-of-field to capture the growth of some plant or fungus. The flexibility of knowing this method far surpasses having dedicated scripts for all these purposes, with no need to re-write or tweak some script if you need it to act different than first intended. Just change your built-in CHDK bracketing method and/or the camera's self-timer options instead.
One more bonus: Using the camera's Custom Self-Timer's counted shots with CHDK's Continuous Bracketing you don't even need a script to take single-event HDR or Focus Bracketing shots. You can manually initiate a counted bracketing sequence this way with each shutter press. No need to even run a script, the camera + CHDK will do it all for you. The flexibility of knowing this method becomes limitless.
One down side to this method is that your camera's self-timer indicator will light up for each shot taken. For cameras that use the AF illumination LED for this purpose, that can cause a distracting environment or even be unaccepable for a given subject matter.