Please explain why objects can be seen more clearly when looked through a small hole. Is this because of the diffraction of light? Thanks in advance 😊.

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    $\begingroup$ ..... Maybe it's just me, but I see things more clearly when I don't have to look at them through a small hole $\endgroup$ – Jim Aug 30 '16 at 13:02
  • $\begingroup$ @Jim You may have seen people looking at an object squint or look through a gap between their fingers? Reduction of the aperture of the lens which is used results in only a small part of the cornea of the eye being used and for many people a sharper image. $\endgroup$ – Farcher Aug 30 '16 at 16:20
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    $\begingroup$ Possible duplicate of How "How to See Without Your Glasses" works? $\endgroup$ – ptomato Aug 31 '16 at 5:01
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    $\begingroup$ If this really makes the image better, your glasses are not strong enough, as your optometrist will be delighted to tell you for a fee. $\endgroup$ – user10851 Aug 31 '16 at 5:22
  • $\begingroup$ @ChrisWhite I'll tell you that too for half what the optometrist will charge you. Can't beat that deal $\endgroup$ – Jim Aug 31 '16 at 12:23

No, it's not because of diffraction. Diffraction is only most observable if the source is monochromatic, and the size of the hole is comparable to the wavelength of light (approx. 400-750nm).
You might have blurred vision, or the object you are looking at may not be in your seeing range, maybe because you are near or far sighted. As a result, the image formed from the incoming light may not converge perfectly or accurately on your retina,
Looking through a small hole narrows the source of incoming light, and thus making the image formed on your retina seem more focused.
This has a similar analogy to cameras. If you want to capture a picture in which almost everything from near to far will be focused, you will have to narrow the camera aperture, but the drawback is that there is less incoming light so you have to lengthen the exposure time (which motion-blurs images of fast moving objects). On the other hand, if you want the picture to have an effect which focuses a specific object, and blurring out the rest, you have to widen the camera aperture, then adjust the focus to focus the object.

Below is a sketch of the image formed on the detector when incoming light is out of focus (1st setup), with aperture/hole (2nd setup), correct focus(3rd setup).
enter image description here


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