crn3371 wrote in post #14250582
The only way you get that shutter speed without changes in iso or aperture is by having the flash fire, which auto does by default.
Yeah, I agree. If your aperture and ISO caused the camera to select 1/2 second for correct exposure (which given your settings, indoors, sounds about right - normally indoors you need a faster lens than that and still have ISO up around 3200 at the very least) then putting it into auto would cause it to pop the flash up and use that to light up the room. In that case, nothing unusual is going on, you just had the wrong start point in Av, causing the camera to have to use areally slow shutter speed for correct exposure. Next time, just see what shutter speed the camera is giving you and if it is too slow, either open the aperture (if you can) or bump up the ISO. In this case you really needed to do both to get a sensible speed.
If you compare Av to full auto outdoors, in decent light, you should get the same exposure level (although not necessarily the exact same settings) as the camera won't need to use the flash.