The best camera is the one you have with you.
—Plato
Since the iPad is easily one of, if not the, largest camera viewfinders I can think of, it makes sense that Halide, a pinnacle of camera apps, recently arrived on it.
Among its many great features for crafting a great shot in both automatic and manual modes is a focus loupe. If you tap the AF (auto focus) button at the bottom, you can dial in focus on your own.
To ensure a sharp image, tap the plus (+) button in the focus tool for a sort of super magnifying glass in the middle of the viewfinder. This zooms in on a small detail of your subject so you can make it’s in focus.