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.

  • I cannot remember for sure if the 450D offers that feature, but is it possible that you set your ISO from Auto to e.g. 100? To me, it seems that your camera decided that it is way too dark - and it cannot alter the setting because (maybe) 10" is the upper limit for automatic exposure times and 3.5 is the widest aperture your lens offers. – flolilo May 19 '18 at 20:27
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    Why do you expect the faster shutter speed and smaller aperture? Is your scene particularly bright? – mattdm May 19 '18 at 20:33
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    If you take a picture with these settings, does the result appear to be correctly exposed? – mattdm May 19 '18 at 20:39
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    Yeah, this sounds like a different problem than I expected. It's helpful to provide this kind of information up front! – mattdm May 19 '18 at 20:46
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    Your problem was that you wanted to adjust the shutter speed. However, it sounded like in P-mode, your exposure settings were completely stuck and you need help with that. To me, that is at least close to X-Y. – flolilo May 19 '18 at 21:22

In P (Program Auto Exposure) mode, shutter speed 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 exposure compensation (press the 'Av[+/-]' button while turning the main 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.

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    To be fair, your needs and mine seem to be mutually exclusive: I love that the ISO stays the same. :-D But granted, there's no way to teach the camera a different behavior - except with higher-range cameras that offer custom-modes. – flolilo May 19 '18 at 20:41
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    "Program mode" and "Program auto exposure" are both valid ways of referring to the same thing. – mattdm May 19 '18 at 20:44
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    And yes, shutter speed could easily increase a lot when moving to spot metering if a less targeted metering mode is being fooled by dark backgrounds. – dgatwood May 20 '18 at 5:53
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    @EricDuminil I don't think he is saying those modes are design flaws. What he is saying is that he wishes he had the option to set the camera so that each exposure mode would independently "remember" what the ISO was set to the last time that mode was used. As it stands now, if I'm shooting in P mode at ISO Auto, go to M mode, change the ISO to 100 while shooting in M mode, then go back to P mode the ISO will still be at 100, rather than return to ISO Auto where it was when I last used P. – Michael C May 20 '18 at 23:29
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    @flolilolilo Doh! But there is no "aperture control dial" on any Canon camera. Thanks for the heads up. I'll fix it. – Michael C May 21 '18 at 1:00

I will try to collect all the pieces from all comments and the question.

Note: Most information about this can be found in the camera's manual, which I tried to link accordingly. This is a rough explanation; some things are described in great detail in the manual, other things can be found on photo.stackexchange.

Am I not able to pick the shutter speed freely in P mode?

No, you are not. p. 56 in the manual offers the following information about P mode:

To obtain a good exposure of the subject, the camera sets the exposure (shutter speed and aperture) automatically.

In P mode, you can either change the exposure compensation (see below), the ISO, and/or the relation between shutter speed and aperture. So if you want to have a fixed ISO of 800, but switch from f/4 and 1/250" to something with a greater depth of field and/or more motion blur, give the main dial a push. 6 clicks and it should become ISO 800, f/8 and 1/60", which offers the same exposure value.

How do I change the shutter speed?

To set the shutter speed, use either Shutter-priority (Tv) mode (only setting the shutter speed) or Manual (M) mode (setting both aperture and shutter speed). Bulb (B) mode would also work, but you would have to hold the button as long as you want the exposure to be - not useful for anything below 1", and usually not really useful without a timer-controller remote shutter control.

Is metering and EV Scale related?

Yes, it is. The EV indicator (p. 18 for the LCD representation, p. 19 for the viewfinder one - and p. 78 for general information.)

The EV indicator shows either your dialed-in exposure compensation (in all modes except M and B) or the result of the camera's metering (in M mode).

Think of the EV indicator as temperature readout display / adjustment knob, while the metering is the thermostat itself. You can see how hot (light) it is via the display or you can adjust the temperature (exposure compensation) via the display, while the thermostat (metering) is then working with your values and trying to get the radiators (aperture, shutter, sensor) to achieve the desired values.

Therefore, when you set exposure compensation to 0, the camera will try a "neutral" approach: a grey card should come out perfectly grey. If your shots are overexposed (because most of the subject is black), you can dial in a negative exposure compensation (left side of the scale), while for underexposure (because much of your subject is white) needs a positive compensation (right side of the scale).

In M mode, you have to do your own exposure - and the EV indicator helps you at that: it shows you how the camera believes your shot will be exposed. This is not as good information as a histogram (or, even better: a waveform), but it offers a bit of orientation.

Should shutter speed increase like this because of the change to spot metering?

Metering (p. 77), on the other hand, defines how the camera evaluates the frame. Spot metering, for example, will just evaluate the middle of the frame and nothing else. So if the middle of your frame is pitch black, but the surrounding area is white, then your exposure will be quite bright. As a rule of thumb, spot metering is best left alone unless you really know what you do.

  • This summary is awesome! – Anders Lindén May 19 '18 at 21:58
  • @AndersLindén Glad you like it. :-) – flolilo May 20 '18 at 1:41
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    The 450D offers a bulb setting in M mode. 'Bulb is the last shutter time just past 30 seconds. – Michael C May 20 '18 at 5:22
  • @MichaelClark Ah, I thought so but couldn't remember, and being a bit lazy, I just took a look at the 450D's mode wheel. Will change that ASAP. Thanks! – flolilo May 20 '18 at 8:12

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.

  • Now, when I tried to change the shutter speed (in a dark room), I could not pick a shutter speed smaller than 1"6. Am I not able to pick the shutter speed freely in P mode? Is there a restriction on how low value I can choose? – Anders Lindén May 19 '18 at 20:40
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    @AndersLindén, "P" mode is "semi-automatic" mode -- the camera will give you some control, but won't let you do anything it sees as messing up the shot too badly. If you want full control over exposure, switch over to "M" mode. – Mark May 20 '18 at 9:46
  • In fact, I'd say P is a mostly automatic mode, which allows a little bit of override. Use Tv or Av for specific control over shutter speed and aperture (respectively), or M for total control. – mattdm May 20 '18 at 15:36

On Canon camera: frame the picture, press the star button to set the exposure (without pressing the shutter button). Use (front on my M5) scroll wheel to exchange aperture for shutter speed. Then press shutter.

Once exposure is set by pressing star - not only can you exchange A and T as above, but if you press ISO button you can use the rear dial (canon M5) to adjust ISO. Very useful.

(On my LX100 exposure is continually minitored and values continuously visible, and in p mode you can exchange values by scroll wheel all the time (no star press needed))

Hope it makes sense.


If you want to change shutter speed, ISO and aperture, use M(manual) mode.

In manual mode you can change everything.

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