How to Determine Specific Screenshot Size(s) for Multiple Views?

Hi, I want to take multiple screenshots of my scene but I want all of the screenshots to be the same aspect ratio. 4:2 aspect ration for example. How would I do this?

Is it possible to render a screenshot from a camera set to a certain size?
Can I set the camera to render 3000 x 1500 px. (For example) and then create multiple cameras to capture stills of my scene?