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Forum: Troubleshooting and Beginner Help
11-14-2014, 04:45 PM
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It depends on the mode you choose and whether you have set a fixed ISO or Auto-ISO. There are three settings that control exposure. The camera has a mode for each one to allow you to control it directly. For example, Av mode means you set aperture directly. If you choose a single setting for ISO, the camera doesn't change that either in Av mode, you have to control that too. So the only thing left for the camera to alter is shutter speed. Tv mode is similar with a fixed ISO - the camera changes aperture. In TAv mode, you have control over shutter speed and aperture directly so the camera only has ISO control. ln Sv mode, you control ISO. Shutter speed changes with compensation until the camera hits its minimum or maximum shutter speed. I think aperture is set to the "program line". The K-50 doesn't allow you to set the program line; top-tier cameras allow you to change it for sharpness or depth of field or other stuff. Program mode lets the camera control aperture and shutter speed on its own, also referring to the program line. Exposure compensation can change both those settings. (Aperture seems mostly controlled by the program line on my camera.)
Setting the ISO to Auto ISO appears to make the camera throw all that logic out the window. :) In Av or Tv modes, exposure compensation raises or lowers ISO first, until the limits you've set on Auto ISO are hit. Then the camera adjusts the remaining parameter it controls. In P mode plus Auto ISO, ISO changes first, then shutter speed and aperture affected by the program line. TAv already has Auto ISO and in Sv it makes no sense.
Green and B mode don't allow exposure compensation.
M mode is a special case because you are supposed to be setting all the stuff yourself directly. You compensate by directly changing the setting you want to change. However, Pentax allows exposure compensation to change the meter reading up or down. No settings are changed directly, but if you are taking shots under conditions where the meter is going to be consistently off, like in the snow, you can bias the meter to overexpose, then use your settings to get a nice zero setting. It's a convenience feature. Auto ISO doesn't work in M mode - Pentax has TAv mode for that.
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