I've made an attempt to start documenting the new Custom Auto ISO for the 1.2.0 user guide.
http://chdk.wikia.com/wiki/CHDK_1.2.0_User_Manual#Custom_Auto_ISOBefore we lock down 1.2.0 as the stable trunk, I'd like to do some cleanup of this function & its UI so I thought I'd re-open this thread.
First of all, to answer msl's question from above, there are basically two changes to this module vs the old code :
- there is an additional [minimum shutter speed & maximum ISO pair] added - to be used when the camera cannot keep the ISO & Tv setting within the original range
- there are three new "exposure" compensation parameters that look at the histogram for the scene and allow you to specify a fixed exposure offset if a user defined number of pixels exceeds a user defined exposure threashold

Simple items to be cleaned up :
1) Max ISO HI (x10) menu item is in the wrong place - should be below Max ISO Auto
2) Delete the word "Second" from two menu lines - it should be just "Alternate Min Shutter Speed" and "Alternate Max ISO" - the word second is redundant and it makes the menu lines too long for my cameras
3) ISO menu items that accept numeric values as (x10) are confusing. Just use regular numeric inputs. Or better still an enum'd range of choices.
More Interesting Questions :
1) The SX230, SX240 and SX260 seem to interpret the menu ISO values as "real" ISO value. All other cameras treat the menu entries as "Market" ISO and do a nasty hack to convert them to "real" ISO. This makes no sense - it should be one way or the other and the default for CHDK is usually "real" value AFAIK.
2) Similarly, the SX230, SX240 and SX260 handle the exposure compensation differently. From what I can tell, they apply the compensation in all situations. Other cameras only do so in "day light mode" - which seems to be defined as the ISO value not being at one of the upper limits. Again, why are those three cameras different.
3) Finally, why is the whole exposure compensation mechanism embedded in the AutoISO menu? Its more like a tweak to "P" mode that just happens to get enabled when you enable AutoISO.
Comments?