geometric-opticslensesopticsrefraction
I'm doing magnification and lens in class currently, and I really don't get why virtual and real images are called what they are.
A virtual image occurs the object is less than the focal length of the lens from the lens, and a real image occurs when an object is further than focal length.
By why virtual and real? What's the difference? You can't touch an image no matter what it's called, because it's just light.
which as far as I know is formed when the light diverges?
The lens tries its best and makes the light less divergent but is not powerful enough to make it convergent.
What you are asking for is a virtual intermediate image to the left of the first lens light from which is focussed a second lens.
Here is a possible arrangement of lenses where the first lens produces a virtual image and the final image is at infinity.
This is the ray diagram for a Galilean telescope which is much shorter than a conventional refracting telescope where the intermediate image is never formed and is said to be a virtual object for the second lens..
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:
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.
Best Answer
You can project a real image onto a screen or wall, and everybody in the room can look at it. A virtual image can only be seen by looking into the optics and can not be projected.
As a concrete example, you can project a view of the other side of the room using a convex lens, and can not do so with a concave lens.
I'll steal some image from Wikipedia to help here:
First consider the line optics of real images (from http://en.wikipedia.org/wiki/Real_image):
Notice that the lines that converge to form the image point are all drawn solid. This means that there are actual rays, composed of photon originating at the source objects. If you put a screen in the focal plane, light reflected from the object will converge on the screen and you'll get a luminous image (as in a cinema or a overhead projector).
Next examine the situation for virtual images (from http://en.wikipedia.org/wiki/Virtual_image):
Notice here that the image is formed by a one or more dashed lines (possibly with some solid lines). The dashed lines are draw off the back of solid lines and represent the apparent path of light rays from the image to the optical surface, but no light from the object ever moves along those paths. This light energy from the object is dispersed, not collected and can not be projected onto a screen. There is still a "image" there, because those dispersed rays all appear to be coming from the image. Thus, a suitable detector (like your eye) can "see" the image, but it can not be projected onto a screen.