Lost your contact lenses? Crushed your glasses? Well you need stare at blurry public transport signs no longer, as simple physics can be exploited to give your vision a small boost using just your hand.
The 'trick' was posted in YouTube video form by the channel Minute Physics and has been stunning bespectacled users in the hours following.
It's very simple:
Make a tiny hole with your finger (curling up index finger works best) and look through it.
Whatever you're viewing, be it text, object or vista should appear considerably clearer.
It is hardly a replacement for corrective optical devices but a pleasing 20-second time waster all the same.
"I am very nearsighted, and I could read the text on my book across the room. Incredible!" one YouTube user commented.
"It works! That’s incredible! I’m actually stunned right now, this is great." said another.
There's a full explanation of how the trick works in the video, but here's the TL;DR:
Your eyes' lenses focus spread out light to create a crisp image on your retina (unless they're damaged, causing you to need glasses), with eye muscles squeezing them so we can focus at different distances.
Unlike a lens, a pinhole or other small opening can focus light coming from any distance. Because it's such a small opening, it only allows light to come through in one place, and thus in only one direction from any particular source, so there's no blur, and everything is in focus.
Small holes create crisp images by blocking rather than focusing light though, so the images are much darker, which is one reason why we don't use them for glasses, contact lenses, telescopes etc.
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