looksharp65
Well-known member
Sancho once coined a phrase about binoculars merely being tubes with glass in the ends.
There's a deeper truth into it, remembering they're afocal systems.
If you look up the sky, then put a 10" wide pipe in front of your face, the sky will not appear darker. And if you take a long black 1" pipe to look through, the brightness of the light in the tunnel is constant all the same.
It might in fact appear brighter than in the first instance, but that's because the eye struggles with the harsh contrast, trying to compenate for the dark pipe wall.
That's essentially everything there's to it. The beam pencil of parallel and diverging light rays isn't somehow compressed, increasing the photon density or speed. It's just a seemingly magnified slice of the reality.
Like David pointed out, it's about modified observation angles.
//L
Edit: Again, the light falling on the iris is "lost" but this does not reduce the brightness. As soon as the exit pupil is smaller than the observer's pupil, brightness will decrease.
There's a deeper truth into it, remembering they're afocal systems.
If you look up the sky, then put a 10" wide pipe in front of your face, the sky will not appear darker. And if you take a long black 1" pipe to look through, the brightness of the light in the tunnel is constant all the same.
It might in fact appear brighter than in the first instance, but that's because the eye struggles with the harsh contrast, trying to compenate for the dark pipe wall.
That's essentially everything there's to it. The beam pencil of parallel and diverging light rays isn't somehow compressed, increasing the photon density or speed. It's just a seemingly magnified slice of the reality.
Like David pointed out, it's about modified observation angles.
//L
Edit: Again, the light falling on the iris is "lost" but this does not reduce the brightness. As soon as the exit pupil is smaller than the observer's pupil, brightness will decrease.
Last edited: