What would be the best way to use an aperture setting? Via Av mode or via CHDK overrride?
In theory, either should be OK. I suggested using canon controls because they are less likely have bugs or special quirks than CHDK controls.
In Av mode aperture dial goes to 8 but the Av override goes to 16. (does anything over 8 work on the sx260?)
Maybe, maybe not. In general, it's likely that you can go higher than at if you are zoomed in with the optical zoom, but the exact details are up to you to determine by experiment, if you care.
An example on sx160
http://chdk.setepontos.com/index.php?topic=12297.msg121510#msg121510CHDK mode is easiest to do; also in there I can override the distance to infinity.
Regarding the video you sent me in PM:
I don't see any obvious defects except for a very small amount of flicker. I'm not sure which "darker spots" you are referring to, I see shadows on the ground and birds (and maybe bugs or other debris close to the camera) on the sky.
As c_joerg says, you always have to trade how much over exposure you want to accept against how dark you want to allow the rest of the scene to get. The script offers you a lot parameters to adjust this, but you will probably need to do many runs to get a good feeling for how they work. I'll try to provide a few comments suggestions.
First, a general description of how it works:
* The script uses two measurements to control exposure: A "meter" area centered in the scene, and a histogram of the entire scene.
* The exposure system tries to keep the average value of the meter at some target exposure value, and uses the histogram keep over and under exposure within some limits.
* By default, the meter is 30% of the sensor width and height, something like spot metering mode in the canon firmware. Stuff outside of this area only influences exposure if it reaches the histogram limits.
* By default, the target exposure value for the meter is a "neutral" exposure, roughly what what Canon AE would give if you aimed the camera at a uniform grey subject.
* The meter target value, limits, and balance between meter and histogram control are all adjustable in the script settings. The individual settings are described in the readme.
Some notes on this specific run:
* Meter was the default 30%, which is mostly sky in this scene.
* The log shows that the exposure was almost entirely driven by meter. The meter_weight, over_weight and under_weight columns show the relative contribution of meter and histogram over and under exposure limits.
* Since you set Underexp thresh to 0, under exposure is ignored. The under_frac column shows there was substantial under exposure, with 15-20% of the scene -4 ev or below.
* There was some over exposure toward around 3/4 of the way through the run, but over_weight never exceeded 1 (except the very start before the algorithm settled), so it had very little impact.
Some things you could do differently
* In a normally composed landscape scene, the sky is bright and should be more exposed than "neutral". So if your meter mostly on the sky, you may want to use the script "Ev shift" option to increase the target exposure. I'd suggest +1/4 to +1/2.
* Alternatively, you could use a larger meter, so it would include the ground. You can use something like 90% if you want.
* If you had under exposure protection enabled, it would have pushed the exposure higher until the sky started to hit the over exposure and / or meter high limits. You can use the "max weight" and "prio" options to control the relative influence if there is both under and over exposure.
* Since the meter is mostly on the sky, clouds moving by cause the brightness of stuff on the ground to change even when the actual lighting hasn't changed. You can use the "Bv Ev shift" option to reduce this effect. This adjusts the target exposure by the absolute brightness of the scene. I find a value around 30% gives reasonable results. The "Bv Ev shift base" option controls sets the brightness at which there is no shift. "First" uses the initial exposure. A well lit subject in daylight would be around 10.
