Are you referring to using averted vision to better see dim objects in the sky?
Your eyes have 2 types of sensors - rods and cones. The cones come in 3 types - each sensitive to a different color. The rods are about 1,000 times more sensitive to light (and more sensitive to motion) than the cones, but are not color sensitive. Because there are more cones in the center of your eye and more rods at the edges, your sensitivity to light is better in your peripheral (or averted) vision, giving you better night vision.
How about when looking through a pin hole? If I don't have my reading glasses and I'm shopping, I want to read the price tag. If I make a very small hole by curling up my index finger and putting it up to my eye, I can see a small area like a price tag just fine. IT REALLY WORKS!!!!
The well-known pinhole effect has a simple explanation.
Refraction occurs when light rays are bent in passing through the interface between two different materials, such as at the surface of a lens. The amount of bending depends on the angle at which the rays strike the surface. Light rays which strike perpendicular continue in a straight line with no bending at all.
In a system of one or more lenses aligned along a central axis (such as the cornea and lens of your eye) the axial rays go straight through, while the off-axis rays are bent in varying amounts. In a perfect optical system the lenses bend all the rays just the right amount to form a clear image. Otherwise the image is blurry.
A pinhole selects just the central (axial) rays which inevitably travel in a straight line without bending, while it excludes the rays that would have to bend just the right amount to form a clear image. In photography, small apertures produce clearer images for the same reason.
The downside is that fewer light rays make the image dimmer. I hope you're reading those price tags in bright light!
Posts: 1967 | Location: U.S. | Registered: 06-03-02
