Photography idiot

"Focus" and "zoom" are two different concepts.

The principle of "zoom" is to change the focal length of the lens by adjusting the distance between lens groups inside the lens. Generally speaking, if you regard the lens as a convex lens, "zooming" is equivalent to changing a convex lens with greater curvature (or smaller curvature) and changing the magnification of the image.

And "focusing" is not to change the focal length of the lens, but to adjust the distance between the lens and the photoreceptor (in principle, the whole front and back translation of the lens group), so that the focal plane of the scene falls right on the photoreceptor, so that the shot scene is the clearest (while the scenes before and after the shot scene are not so clear). If you shoot with SLR and telephoto lens, this feeling will be very profound. For example, in a photo, people are photographed very clearly, but the background is blurred. At this time, the focus is on people.

Therefore, if you want to take a wider range of photos, or zoom in on distant scenery, you must "zoom".

And if you want the subject to get the clearest shot, then you have to "focus". When you press the shutter halfway, a focus box will appear. If you want which part of the photo is the clearest, you should use this focus frame to frame the subject. Manual focusing is the same, just adjust to the clearest subject.

I hope my answer is useful to you.