One of the most commonly asked questions regarding depth of field is, ‘How do I get front-to-back sharpness?’
The usual advice for beginners is to focus a third of the way into the scene. This is because depth of field extends twice as far behind the point of focus as in front of it.
Infinity - what is it?
In photographic terms, infinity can be one of two things:
"Focused on something infinitely far away",
or “an infinite amount of focus”, so everything possible within the frame is in focus.
Focusing on something infinitely far away is better for astro-photography, while an infinite amount of focus is better for landscape photography.
Hyper-focal Distance - what is it?
Hyperfocal distance is defined as “the distance into the scene, when the lens is focused at infinity, where objects from half of this distance to infinity will be in focus for a particular lens”.
Alternatively, Hyperfocal distance may refer to the closest distance that a lens can be focused for a given aperture while objects at a distance (infinity) remain sharp. The Hyperfocal distance is variable and a function of the aperture and focal length.
In other words, focusing at the optimum focal distance, (73 feet), for a 50 mm lens set at f/5.8, will result in an image that is in focus from 36.5 feet, (half the focal distance), to infinity.