I have been trying to take some photos with the camera in aperture priority mode but have found the ISO is not automatically adjusted. Can someone tell me if and how i can use auto ISO in aperture priority mode? I am using a Nikon D3300.
In A,S,P,M modes, you have to turn Auto ISO on, in Setup menu, see manual. Auto ISO is automatically ON in Auto mode, but is not automatically ON in A,S,P,M modes, not unless you turn it On.
User has choices unless in Auto mode. In A,S,P,M modes, you manually open the popup flash if you want to use it, and don't if you don't. You set Auto ISO On if you want to use it, or don't if you don't. You set Auto White Balance On if you want to use it, and don't if you don't. You set which ever Color Profile you want, like Standard, or Neutral or Vivid, etc.
There is a much more complete manual called D3300 Reference Manual, available free from Nikon at http://downloadcenter.nikonimglib.com/en/products/21/D3300.html
Then (page 227 in D3300 Reference manual), in dim light in A mode, Auto ISO will first decrease shutter speed as needed, until it reaches the Minimum Shutter Speed in the Auto ISO menu. Then shutter speed will hold there, and ISO will be increased. Until it hits Maximum ISO there, when it holds, and shutter speed will again begin decreasing (below the specified Minimum).
So.... this Auto ISO Minimum Shutter Speed is important, in that it WILL BE the shutter speed used anytime Auto ISO is in effect and increasing. Try something like 1/80 or 1/100 second.
You likely will not see any ISO change in P mode either, P mode will not change ISO on its own. But you can force change with P mode Flexible shifting.