Why does looking through a traw improve the focus or resolution you see?

[philip041]

When I curl my hand up and look through it, even though I have terrible eye sight I can read the title of a book on my shelf even though I can't if I'm not wearing my glasses. Why is this? I just had a lecture on SNOM, (Scanning Nearfield Optical Microscope), where the lecturer made a comparison with this.

 

[mgb_phys]

Your imperfect eye doesn't focus all the rays of light to a single point
The rays at the edge of the field of view have to be bent most and so are affected most by any error in the bending. By putting a hole in front of your eye (it works with just your fingers making a loop) you limit the rays to only those near the axis which are ebtn least.

The same thing applies to all optics, it's why your camera takes sharper pictures with the iris stopped down.

 

[Cantab Morgan]

You can also read better when in bright light, and not only for the obvious reason. When your eye is stimulated by bright light, your iris expands significantly, constricting your pupil to more of a pinhole.