Quote "Even if things worked "correctly" the live view would only show you whatever settings you used in the preceding shot."
I'm a bit confused ... it should/would, but it doesn't? ... should ISO override not work like Tv and Av overrides do now?
Based on what you're saying I tried this ...
... always staying in M mode and always using CHDKPTP only, I set the camera to 1/2s f2.0 and ISO 1600. For simplicity keeping iris fully open and not caring about it here, my liveview brightness is governed by the 1/2s and ISO1600 to be a bright view.
> (1) I press the SHOOT button I get an image at 1/2s and ISO 1600, with correct EXIF tag. That's OK.
> (2) Next, if I type shoot -tv=1/4s -sv=800, I get an image at the 1/4 the brightness level of (1) & EXIF tag 1/4s & ISO 800 // so far so good. This operation should *not* change the original camera settings of 1/2s and ISO1600, and it does not. Right?
> (3) But right after the shot, my liveview brightness goes *dim* to an *equivalent* ISO setting of 100 (gets dark) even though the Canon display icon is still displays the original setting of ISO 1600.
> (4) The important word above is *equivalent* because 2 days ago I estimated the unwanted darkness value by restoring the original high brightness, and then manually dropping the ISO setting while visually inspecting brightness level until I got the same dark after (3), and that turned out to be ISO 100.
> (5) New today: while still dark after step (3), I again press the SHOOT button but I do *not* get the same image as in (1). Instead I get 1/2s but at ISO 100, despite that the Canon icon still says 1600. Note that the Tv did *not* get changed from the original, as I would expect.
That means my estimate in (4) was correct, so ....
a) after shoot with an -sv parameter the camera does take the shot correctly,
b) but after the shoot it dims liveview to ISO 100 << bad >>
c) ... and ... internally sets ISO to 100 << bad >>
d) but still shows ISO 1600 in the OSD.
e) and ... if I say now shoot -tv=1/2s -sv=1600, I get the same bright JPG as in (1), but liveview stays dark !!!
f) but all SHOOT button shots now come out at ISO 100 despite the ISO 1600 display.
So in essence ... with respect to liveview brightness, the SHOOT button keeps liveview brightness the same, but shoot command when used with -sv, dims the liveview.
I just want to be sure that we are both looking at the same thing. I think something weird happens when I send the camera an -sv in the shoot command that always sets the internal ISO to 100 after correctly taking the shot. Is this your understanding? Is this what you were able to reproduce?