There's nothing to configure, really. As i already said, Corona should give you an optimal quality straight out of the box. There are some controls in render setup>performance tab, like AAvsGI, LSM, MSI and few others, that can be tweaked to try optimize render speed in specific situations, but it's very scene dependent and what's work in one scene, might worsen things in another one. If you don't know exactly what each of these controls are doing, it's much wiser to stick to default settings as this will be much faster than try to find gain minutes of render time by blindly turning the knobs.
Regarding the zoom, i repeat myself again - please provide an example (rendered image, or screenshot) with the issue, otherwise there's nothing to advice you, i'm afraid.
