G3 - P versus A modes

Discussion in 'Panasonic Cameras' started by tonasc, May 14, 2013.

  1. tonasc

    tonasc New to Mu-43

    Apr 26, 2013
    Hi. So the G3 is my first adventure away from compact cameras, so still learning the ropes.

    I'm trying to work out the difference between P and A modes. I know that in P you are supposed to be able to adjust both aperture and shutter speed, but when I turn the dial, the aperture changes with it. The system changes the speed to match it... which is the same as what happens in A mode.

    Am I missing something?

  2. jziegler

    jziegler Mu-43 Veteran

    Dec 15, 2012
    Salem County, New Jersey
    Real Name:
    It sounds like you might be confusing P mode with M mode.

    In M mode, you turn the dial to adjust either shutter speed or aperture, and then press the dial in and you can adjust the other. They are controlled independently, and the camera will not change what you set, with the exception of a variable aperture zoom lens if you zoom in or out.

    In P mode, the dial adjusts either exposure compensation, or program shift. What you are describing is the program shift, where the camera keeps the exposure constant, changing the aperture and shutter speed together.

    I can see how P and A would look the same to you, but where they would differ is going between different subjects or lighting conditions. In P mode, every new shutter half-press will calculate a new exposure that could cause a different aperture to be chosen, or it will change if no shutter speed will result in the metered exposure. In A mode, that aperture will always be used until you change it, even if there is no shutter speed that will result in the metered exposure.

    I hope this helps, please ask again if you need more clarification.
  3. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL

    Only in M (manual) mode will adjusting one control (f/stop or shutter speed) be independent of the other. In any of the automatic modes (P, A, & S) when you override one the other changes in response. The difference between the three auto modes is only in how the camera makes adjustments when the lighting changes:

    A: the aperture is fixed and the camera only alters the shutter speed until the shutter speed reaches a limit in how much it can be adjusted.

    S: the shutter speed is fixed and the camera only alters the aperture until the limit of adjustment is reached and only then is the shutter speed altered.

    P: the camera adjusts both based on some built-in program, or set of programs. Some cameras have multiple "programs" chosen by the camera based on the lens in use.

    When using an auto mode, most camera will allow to to alter the settings. In such cases both the aperture and shutter speed will change so that the overall exposure remains the same.
  4. tonasc

    tonasc New to Mu-43

    Apr 26, 2013
    Thanks both.. That's cleared it up nicely!