If you have a Canon compact camera CHDK is not an option, it's a neccessity.
The fact is: It costs you nothing to have it or own it or install it. It doesn't actually do anything unless you want it to. When you need it (and you will) there is no other solution.
Best first purpose: Override shutterspeed or aperture.
In most compact cameras, you can shoot in manual mode selecting shutter and aperture as you wish and the camera still operates the flash in TTL mode. That is, regardless of your manual settings, the camera will fire and quench the flash for the "best" possible exposure; it will seek a balanced exposure by expertly controlling the flash output.
Experienced shooters take advantage of this (when possible) by selecting an aperture appropriate for the subject, then shooting at several ascending/descending shutterspeeds. Camera TTL logic keeps the subject correctly exposed and rolling through shutterspeeds varies the exposure of the background. This is how to easily obtain just the right amount of detail in the background, or even make it black.
Unfortunately most Canon compact cameras don't do this. CHDK to the rescue.
Example: Use CHDK to override aperture to F/5.0. Set the exposure program to shutter priority. Set ISO to 100.
Now you can shoot using multiple shutter speeds, say 1/60 through ??? The G11 can synch flash as fast as 1/1000, so that is quite a range. Since you are shooting in a program mode ("Tv"-shutter priority), the camera will use TTL metering to quench the flash, so the foreground exposure will remain constant. The changing shutterspeed will obviously affect only the exposure of the background.
In practice, you may have to adjust that f-stop if the background is not bright enough. Alternatively, you can bump the ISO up to 200 or down to 80. It will depend on your camera and conditions. I chose f/5.0 as a starting point because the lens on the G11 is well-behaved there. Your camera may be different.
Example: Use CHDK to override shutter speed to 1/200. Set the exposure program to aperture priority. Set ISO to 100.
Now you can do the same thing as before only shoot with various apertures while CHDK holds the shutterspeed constant. Again you will have TTL flash (because you are using a program exposure mode). The foreground exposure will remain constant while the background exposure will change according to aperture.
Note that these overrides affect every camera mode, even manual. If they are both on at the same time, then that is all you get!
The shutterspeed override requires two fields: The shutterspeed and the "Value Factor" right below it. The shutterspeed override only works when the "value factor" is one. i.e. "1". The only other possible value is "Off" so in effect it turns the shutterspeed override on and off with one click. <Like this>. <Like this a lot>. I tend to use this mode most often. Importantly, I have found that you need at least this much speed (1/200) to freeze the motion of shrimps and antennae. Left to itself, the Canon software chooses 1/60, and its just not good enough.
On the other hand, The aperture override has a singularly impressive feature. On my G11 It lets me stop down to F/16. In practice this is limited to F/11 but still an improvement where depth of field is important. At this setting, the the Aperture override turns off with one button press also because the CHDK menus are sensibly linked at the ends. One step left of "off" is f/16, and ones step right of f/16 is "off".
So there you have it. TTL flash exposure while varying either shutterspeed or aperture.
Impossible to accomplish without this free software. These methods work best of course with cameras that have external strobes, but still hold true for those of you shooting with internal flash and diffuser. You just won't have as broad a range.
Two important things to note:
One
The fact is: It costs you nothing to have it or own it or install it. It doesn't actually do anything unless you want it to. When you need it (and you will) there is no other solution.
Best first purpose: Override shutterspeed or aperture.
In most compact cameras, you can shoot in manual mode selecting shutter and aperture as you wish and the camera still operates the flash in TTL mode. That is, regardless of your manual settings, the camera will fire and quench the flash for the "best" possible exposure; it will seek a balanced exposure by expertly controlling the flash output.
Experienced shooters take advantage of this (when possible) by selecting an aperture appropriate for the subject, then shooting at several ascending/descending shutterspeeds. Camera TTL logic keeps the subject correctly exposed and rolling through shutterspeeds varies the exposure of the background. This is how to easily obtain just the right amount of detail in the background, or even make it black.
Unfortunately most Canon compact cameras don't do this. CHDK to the rescue.
Example: Use CHDK to override aperture to F/5.0. Set the exposure program to shutter priority. Set ISO to 100.
Now you can shoot using multiple shutter speeds, say 1/60 through ??? The G11 can synch flash as fast as 1/1000, so that is quite a range. Since you are shooting in a program mode ("Tv"-shutter priority), the camera will use TTL metering to quench the flash, so the foreground exposure will remain constant. The changing shutterspeed will obviously affect only the exposure of the background.
In practice, you may have to adjust that f-stop if the background is not bright enough. Alternatively, you can bump the ISO up to 200 or down to 80. It will depend on your camera and conditions. I chose f/5.0 as a starting point because the lens on the G11 is well-behaved there. Your camera may be different.
Example: Use CHDK to override shutter speed to 1/200. Set the exposure program to aperture priority. Set ISO to 100.
Now you can do the same thing as before only shoot with various apertures while CHDK holds the shutterspeed constant. Again you will have TTL flash (because you are using a program exposure mode). The foreground exposure will remain constant while the background exposure will change according to aperture.
Note that these overrides affect every camera mode, even manual. If they are both on at the same time, then that is all you get!
The shutterspeed override requires two fields: The shutterspeed and the "Value Factor" right below it. The shutterspeed override only works when the "value factor" is one. i.e. "1". The only other possible value is "Off" so in effect it turns the shutterspeed override on and off with one click. <Like this>. <Like this a lot>. I tend to use this mode most often. Importantly, I have found that you need at least this much speed (1/200) to freeze the motion of shrimps and antennae. Left to itself, the Canon software chooses 1/60, and its just not good enough.
On the other hand, The aperture override has a singularly impressive feature. On my G11 It lets me stop down to F/16. In practice this is limited to F/11 but still an improvement where depth of field is important. At this setting, the the Aperture override turns off with one button press also because the CHDK menus are sensibly linked at the ends. One step left of "off" is f/16, and ones step right of f/16 is "off".
So there you have it. TTL flash exposure while varying either shutterspeed or aperture.
Impossible to accomplish without this free software. These methods work best of course with cameras that have external strobes, but still hold true for those of you shooting with internal flash and diffuser. You just won't have as broad a range.
Two important things to note:
One
CHDK software features; ALL of them, can be turned off instantly by setting the first option in "Extra Photo Operations" to "On". I positively hate that this field is called "Disable Overrides" and that the the choices are "On", "Off" and "Disable". Exactly what are you disabling, eh? Suffice to say
- "Off" and the overrides work.
- "On" and the overrides are disabled, not working, not overriding.
- "Disable" has exactly the opposite effect that you would expect. It disables the disabling of overrides, so they work!
Stick to On and Off.
Two
The [currently] fourteenth feature in the "Extra Photo Operations" menu is:
Clear override values@start
By default, CHDK sets this feature sets this feature to "true"/On/selected. As a result, all the settings you select will be forgotten everytime you power on the camera.
Unless you want to go insane every time you splash, turn this "feature" off. Tell CHDK that you want it to work. Tell CHDK that you will "Disable overrides" when you want all the cool stuff to stop working! Tell CHDK that you want it to remember all your settings: turn this off.
Clear override values@start
By default, CHDK sets this feature sets this feature to "true"/On/selected. As a result, all the settings you select will be forgotten everytime you power on the camera.
Unless you want to go insane every time you splash, turn this "feature" off. Tell CHDK that you want it to work. Tell CHDK that you will "Disable overrides" when you want all the cool stuff to stop working! Tell CHDK that you want it to remember all your settings: turn this off.
Last edited:
