I'm fairly new here (and to DLSR photography in general) so I'm hoping someone can help. While taking pictures in Av mode recently my EOS100D suddenly began doing something weird - seemingly overexposing some, but not all of the photos. It has happened while using 2 different , and it doesn't seem to be due to me moving / pointing the camera anywhere different. So for example, I would be standing in the same spot clicking off photos one after the other (quickly), and then when I look at them some are overexposed and some aren't. Of course I could hear the going slower / quicker at times too - but again this didn't seem to be due to anything I was doing.
It seems to have trouble focusing also as I'm taking some photos - the ones that turn out to be bad (even when the is good) - I can tell when looking through the viewfinder that it isn't focusing properly.
Here is an example of 2 shots I took one after the other. Obviously my position changed slightly in this example but the was the same:
IMG_2528 resized.JPGIMG_2529 resized.JPG
Settings: 1st pic f/3.5, 1/320, ISO400. 2nd pic: f/3.5, 1/100, ISO400
On another occasion I was taking multiple photos from the same position, and as I went on snapping the got brighter and brighter until they ended up looking like this:
Settings: f/4.5, 1/60, ISO100.
By this stage I was fiddling with settings trying to figure out what on earth was going on.
I've tried resetting the camera to factory default settings, taking battery / SD card in and out and turning on and off, looked up the manual for troubleshooting and looked online, and have no idea what to do next. The problem is still occurring, but it still seems quite random - i.e. in a series of 8 shots some will look overexposed to some degree, and some look normal. I've tried lots of different settings / and it's the same problem regardless.
I'd appreciate anyone's ideas / help? Thanks for taking the time to read this, and for any advice or suggestions. Please let me know if you need more info - I read the guidelines and have tried to provide as much info as possible.