Canon Camera Hackers Manual

Contents

4.3 Exposure 31Also, the available correction range is much larger than the two f-stopsprovided by the camera’s native exposure correction. The step size canbe controlled in increments of 1/6 f-stop through the subentry Step size.On cameras where the UP and DOWN buttons are used for chang-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. Pressingthe UP button repeatedly will change the Ev and the ISO speed; theDOWN button will change the Ev and the shooting mode.The workaround is simply to wait a second after each click on UP orDOWN. After that time, the native function will be aborted so that onlythe Ev value is changed. To change the ISO value or the self-timer/seriesmode, simply click faster and afterwards correct the Ev value with theopposite button in delayed fashion. Or, temporarily switch off EnableFast Ev. This less-than-optimal situation will likely change in futureCHDK versions.4.3.2 Custom Auto ISOApart from setting a fixed ISO value in manual mode, the native Canonexposure system provides two automatic ISO modes. These modes try tofind a suitable compromise between sensor speed and exposure timewhen 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 istherefore suited to subject matter without much movement, such as land-scapes or portraits. In contrast, ISO HI puts the emphasis on speed. It useshigher ISO values (resulting in more noise) but shorter exposure times. It istherefore better suited to subject matter with fast movements, such assports, children, animals, etc.Of course, both of these automatic ISO modes are predefined by themanufacturer. The photographer has no chance to customize how theywork. Since the camera does not know how steady your hand is or theminimal shutter speeds required, it can only make worst-case assumptionsthat may result in less-than-optimal ISO settings.Enter the CHDK. The submenu Extra Photo Operations > Custom AutoISO provides you with all the necessary controls to optimize the behavior ofISO AUTO and ISO HI.Let’s discuss the submenu entries one by one:f Enable Custom Auto ISO is used to enable the parameters listed below.When disabled, the camera goes back to the native ISO AUTO and ISO HImechanism.f Minimal Shutter Speed. Here you can set a minimal shutter speed. TheAuto setting can be used when your subject holds still, as in landscapes,portraits, or stills. For moving subjects, this setting will choose aFigure 4-19The Custom Auto ISO submenu