Convex lens in our Eyes

biologylensesopticsphotonsvision

I just learned that our eyes are made up of bi-convex lens, and I know that convex lens are also called converging lens since they converge to form real images that can be caught on a screen. But why is the image as seen by me virtual and erect? I don't see my world upside down or inverted. Also if I am able to see the whole world as a virtual and erect image, then where is the screen?

Are all these some misconceptions or is it just that the brain does the job to invert the image formed by my convex lens and shows me an erect image?

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The image you see is not virtual; it is real. The "screen" is the retina on each eye, and the real image forms there due to the eye lens. The brain then inverts the image to make it appear upright to your perception.

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[Physics] If I reflect light from a projector using a mirror, then is the reflected image real or virtual

The "rule" that real images are always inverted is not correct. That rule might work when you have only a single optical element (like a lens), but not necessarily when you have two or more.

Take a look at this:

enter image description here

That's a real, upright (aka erect) image labeled $I_B$. You can tell it's real because the rays at the final image actually converge at that physical location, unlike virtual images whose location of "convergence" does not actually have physical rays passing through it (only the "backtracking" rays one typically draws).

As for your projector and mirror, you can draw a ray diagram carefully (if you know the internal workings of a projector) and apply the same test to see if the image is virtual or real. But do remember that projectors can be modified so that the image you see is inverted to accommodate mirrors and such. Anyway, to get something projected on to a screen, I do believe the image needs to be real, so I would say it is indeed a real image you're seeing.

Finally, here's a simple example of two elements that again goes against the rules in your book:

enter image description here

The situation above has a real, inverted image using a lens and mirror (a mirror!). Thus, the rules you've been given aren't general enough to deal with multiple-element situations.

[Physics] Is real image formed by a single optical element always inverted and virtual image always erect

A gradient index rod lens will form an erect or inverted image, depending on its length. A SELFOC lens is usually designed to transfer an image from the flat surface on one end of a rod, to the flat surface at the other end of the rod. A SELFOC lens is usually designed to produce an inverted image, but when made twice as long (that is, with pitch 1.0) it forms an erect image. The ray paths for a single pixel on one surface go through the rod as shown below. They come to an inverted focus in the middle of the rod, then back to an erect image at the other end of the rod.

This image is one frame from a video on the Stemmer Imaging website, though there are several companies who provide gradient index rod lenses. This sort of device is sometimes called a "Contact Imaging Sensor", and would be one element of a "line scan bar".

Edit #1 Some other approaches might meet the uniform refractive index, single-element condition:

Retroreflection: A ball lens with a refractive index of 2.0 and a highly reflective coating on its back half will return light to its source. That means that an erect real image is formed from an erect source image.
Fly's Eye lens: A slab of glass or plastic with small lenses on both sides can form an erect image. Each lens on one face of the device forms a small field-of-view erect real image via the corresponding lens on the opposite side of the slab. The lenses and the slab thickness are designed to ensure that the imaging is precisely 1:1, and the images all add up. This is the principle of the contact image sensors (line scan bars), and is a variation on the principle illustrated by @BarsMonster: just build an array of the rod lenses he described, and fuse them together to eliminate boundaries between the rods, leaving only lens bumps on the surfaces. Of course this element can be cast in plastic.

I'm pretty sure two optical surfaces are required, when the refractive index is positive, because we can show that an single optical surface (reflective or positive-refractive) can only form an inverted real image. HOWEVER, negative index materials, in principle, can do it with only a flat, parallel-faced slab. See "Negative refraction makes a perfect lens" by Pendry.

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[Physics] If I reflect light from a projector using a mirror, then is the reflected image real or virtual

[Physics] Is real image formed by a single optical element always inverted and virtual image always erect

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