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the image that we produce inside of our view camera is upside down

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takes a picture with lens

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a clear picture

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takes a picture without the lens

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"all you see is more or less uniform nothing"

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why does this happen?

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light spreads out from a point in all directions

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we assume that but there is proof of this

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you point out an object to a friend and your friend acknowledges that he sees it, too

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light that enters your eyes is a different set of photons than are entering your friend's eyes

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why don't we get a picture of an object if we simply expose film in its present

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you can't have an image without some way to focus light

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the reason is that photons from the light source are hitting the full area of the exposed film

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but if you have a sheet of film, an object emitting light, and between then a pinhole

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then only the light that goes through he pinhole will hit the film, but as it goes through hole, the light from the top of the object hits the bottom of the film and vice versa

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adding a lens to the pinhole will focus the light in various ways, but it remains inevitable that the image created on the film is upside-down in relation to the object which is emitting light

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you can also use a curved mirror

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there are differences between the images that we get with curved mirrors

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there are limitations that we currently have with lenses

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or a lens can be used at the point where the pinhole is

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a lens is very thin at the edges

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however, it is very hard and expensive to make a large piece of class which is thin around its circumference

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this is one of the reasons why refracting telescopes which use lenses instead of mirrors are limited

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the largest refracting telescope is only about 40 inches in diameter

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the lens is shaped as it is so that the light has a way to "know where to go" to create the image

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the principle of least time, by Pierre Fermat

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part of the way our modern lenses of cameras are designed today

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recently people have begun to think about the possibility of making a flat lens

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the way you do that is a very strange idea that has to do with the way light bends when it goes through an object

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but it would enable engineers to make larger telescopes