Custom Auto Iso - Canon Camera Hackers Manual

Also, the available correction range is much larger than the two f-stops
provided by the camera's native exposure correction. The step size can
be controlled in increments of 1/6 f-stop through the subentry Step size.
On cameras where the
ing the ISO setting and for the self timer, however, there is a problem.
With Enable Fast Ev set, these buttons will have two functions. Pressing
the UP button repeatedly will change the Ev and the ISO speed; the
DOWN button will change the Ev and the shooting mode.
The workaround is simply to wait a second after each click on
DOWN. After that time, the native function will be aborted so that only
the Ev value is changed. To change the ISO value or the self-timer/series
mode, simply click faster and afterwards correct the Ev value with the
opposite button in delayed fashion. Or, temporarily switch off Enable
Fast Ev. This less-than-optimal situation will likely change in future
CHDK versions.

4.3.2 Custom Auto ISO

Apart from setting a fixed ISO value in manual mode, the native Canon
exposure system provides two automatic ISO modes. These modes try to
find a suitable compromise between sensor speed and exposure time
when shooting in low light. The mode ISO AUTO puts the emphasis on im-
age quality. It uses lower ISO values and longer exposure times and is
therefore suited to subject matter without much movement, such as land-
scapes or portraits. In contrast, ISO HI puts the emphasis on speed. It uses
higher ISO values (resulting in more noise) but shorter exposure times. It is
therefore better suited to subject matter with fast movements, such as
sports, children, animals, etc.
Of course, both of these automatic ISO modes are predefined by the
manufacturer. The photographer has no chance to customize how they
work. Since the camera does not know how steady your hand is or the
minimal shutter speeds required, it can only make worst-case assumptions
that may result in less-than-optimal ISO settings.
Enter the CHDK. The submenu Extra Photo Operations
ISO provides you with all the necessary controls to optimize the behavior of
ISO AUTO and ISO HI.
Let's discuss the submenu entries one by one:
Enable Custom Auto ISO is used to enable the parameters listed below.
f
When disabled, the camera goes back to the native ISO AUTO and ISO HI
mechanism.
Minimal Shutter Speed. Here you can set a minimal shutter speed. The
f
Auto setting can be used when your subject holds still, as in landscapes,
portraits, or stills. For moving subjects, this setting will choose a
UP and DOWN buttons are used for chang-
UP or
> Custom Auto
Figure 4-19
The Custom Auto ISO submenu
31
4.3 Exposure