Corrective glasses are usually intended to help focus light on your retina. Supposing I had good vision already, but simply wanted more light, could I make glasses that would send more light into my eye without magnifying, focusing, or distorting the image? (Ignore chromatic aberration.)
[Physics] Is it possible to make glasses that make everything brighter, but do not magnify or focus
geometric-opticsoptics
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In the same way as a telescope eyepiece, they create a virtual image at infinity.
In the HUD the objective lens focus the image from a display (on the left in the diagram) and the lens at the front of the HUD reimages it at infinity.
In order to get a large aperture in a small thickness and with low weight they typically use fresnel or holographic lenses.
As you said, the big advantage of the HUD isn't that the user doesn't have to look down at their instrument panel - but that they don't have to wait for their eyes to refocus. It's even more important for military pilots using helmet mounted image intensifiers (night sights) which are focussed for viewing at infinity.
I'll answer your question by order:
Yes, the brain does flip the image that is on the retina.
You are mixing 2 separate things. When an object is placed closer than the focal plane to a lens, there will be no real image, only an 'imaginary image' that is not inverted. When an object is placed farther apart, the lens make the rays cross like you said and when you are looking at the object, you see a real inverted image, so your eyes invert it again and there is a straight image on your retina, but your mind flips everything he sees (because your eye lens) so you see the inverted real image.
Glasses help your eyes bend the light in the right way, you do not look at the image the glasses would produce if they were a foot away from your face.
I hope it helped! If you have any more questions you are welcome to ask
Best Answer
First, let me try to clarify the question, because not everyone seems to get it ("where would the photons come from?"). If I'm buying binoculars, I might choose from 8x24, 8x36, or 8x50 binoculars. The first number is the magnification; 8x for all the examples. The second number is the size of the objective in millimeters, 24 to 50 millimeters in the example. All else being equal, the larger objectives will gather more light, and produce a brighter image. The 8x24 and 8x50 binoculars will deliver the same 8x magnification, but the 8x50 pair will be brighter.
So it's reasonable to ask if you could make 1x binoculars that have a big objective that brightens the scene in front of you. There's no conservation of energy issue here; the larger front objective would gather more light. The problem is that there's a relationship between the magnification and the sizes of the entrance and exit pupils:
If you create a binocular with an entrance pupil (objective, basically) that's larger than your eye's pupil, so that it can gather more light than your eye's pupil, then at 1x magnification, the exit pupil is going to be just as big as the objective lens. And since that's bigger than your eye's pupil, the "extra" light is going to run into your iris instead of going through the pupil, and you will gain no advantage from it.