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When you place two lenses one behind the other, the effective focal length is a function of their distance. This is the principle behind a zoom lens - with the same pieces of glass, a zoom lens achieves a range of distances. What you are describing is the simplest case of a zoom lens - just two elements. The first element is the cornea + lens in the eye - ...


0

In my answer to this question: (What is the sun's spectral series?), I give a very detailed answer about why mixing colours of light produces other colours and how it is purely a result of biology and evolution. I also delve a bit into the structure of the human eye and why, in fact, only three colours are necessary to reproduce all of the colours we can ...


2

A "normal, healthy" human eye has two types of light-sensitive cells in the retina: rods ("color blind", but capable of sensing low light levels) and cones: cells that are sensitive to different bands. See this figure for their relative sensitivity (from http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colcon.html) When you look at a spectrum of light, ...


1

The cells in our retina that detect by frequency (read: colour) detect most strongly in three slightly different bands we know as Red, Green and Blue. To make a slight correction I would say an incadescent bulb is quite far from white, so I would rather proceed talking about sunlight on a clear day. The reason why sunlight appears as white as say a white ...


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I am just guessing on this based on the reference you posted in the comments. Sometimes dB's are referenced to a max level, like with audio at 120dB. In this case they look at the difference between the maximum. In your case, 10,000 is the max, or 40 dB. Based on this scale comparison: I would guess apostilibs to dB is done like this: $dB = 40 - ...


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This is a real effect, but it doesn't have anything to do with coma or any of the optical aberrations. It is caused by the fact that the effective focal length shortens as you tilt a lens. When your eyesight gets worse, you need a stronger focal length lens in your eyeglasses, and tilting the lenses has this effect. The problem with doing this all of the ...



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