Can´t control shutter speed/aperture values in P mode, half clicking the shutter

by Anders Lindén   Last Updated May 19, 2018 21:18 PM

When I half click the shutter on a Canon XSi/450D in program mode to setup shutter speed and aperture, theese values will show up in the topmost two boxes in the interface (starting from yesterday):

10" F3.5

What is this?

I expect something like

1/90 F5.6

Also, if I change the values using the index finger on the dial, the shutter speed will not change. It seems to be stay to a couple of seconds.

How do I change the shutter speed?

Edit: The ISO has been 100 when the problem started and have been set to 400 later on, still having the problem.



Answers 2


10" F3.5

What is this? I expect something like

1/90 F5.6

" is the symbol for seconds. It means that the camera has chosen an exposure time of 10 seconds, and an aperture of f/3.5 (likely the widest possible). That indicates that the camera is metering the scene as quite dim, and is choosing values to let as much light in as possible in order to produce a normally-correct exposure.

mattdm
mattdm
May 19, 2018 20:36 PM

In P (Program Auto Exposure) mode, exposure and aperture are automatically set. The only thing you can control manually is ISO (unless you put it into auto ISO mode, in which case they are all automatically set. The only thing you can do is use the aperture dial to underexpose or overexpose your shots by a relative number of stops.

The behavior you describe suggests that you are in a dark environment (10 second exposure, wide open) and you turned off auto ISO, possibly while shooting in a different mode. Annoyingly, Canon's ISO mode is not dependent on the position of the mode dial, so turning auto ISO off while in manual mode means you get stuck at a fixed ISO when you put it back into a more automatic mode.

This is, IMO, a fairly serious programmer error/design flaw, as I have almost never wanted manual ISO when in program AE mode, and have absolutely never wanted automatic ISO when in manual mode. This is the single biggest usability flaw in the Canon system, bar none, IMO. Sorry you ran into it. Trust me, it happens to all of us.

dgatwood
dgatwood
May 19, 2018 20:39 PM

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