What you're describing my friend is called: Accommodation; it is mostly involuntary (some people can accommodate voluntarily though)
When we look at near objects - the brain signals a smooth muscle in the eye (called the ciliary muscle and controls the shape of lens) to contract, this causes the lens of the eye to become rounder and kinda fatter and that will give us a clear near vision. When we look far ahead for distance the muscle relaxes causing the lens to become flatter and that gives us a focused distance vision.
What you're doing is essentially accommodating- and changing the focus, or more accurately, bringing the focus closer to your eyes, therefore things get fuzzier beyond that point.
Try these couple of things: first look at a distant object, blur it, hold the blur and then slip another object such as a pen in your line of vision and closer to you, you'll see that it is clear/er. Also try to hold something very close to your nose and you'll see that you can't really blur it or at least not for too long. That's because accommodation is limited (and gets worse as we age)
Anyway nothing wrong with accommodating and it's normal- hope that helps.
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