There are a lot of posts regarding real vs virtual images. I 'think' I understand the distinction clearly, however, there is one thing that I can't quite wrap my head around. What is the "shape" or apparent shape, of a virtual image?

I understand that I can photograph a virtual image because a real image is eventually formed on the sensor. I am not sure what it means for a camera to focus on a virtual image though.

I assume that a virtual image from a mirror, will remain the same proportion to the object, but if a virtual image is formed from a lens, does it become "curved"?

In case I'm not asking the right questions, the very specific use case that I'm trying to understand is a camera in a underwater housing, looking out a curved glass port into water. Everything I have read states the camera focuses on a virtual image that and that the virtual image is curved.

However, all of the lens examples I've found show 2 dimensional - if the image flipped, where it's located, and it's magnification. From that, I don't see how I could determine if a virtual image is curved. Can anyone help guide me to what I'm missing here?



To give a simple answer: a virtual image has the same shape as it's 'real' counterpart (up to magnification and flipping, maybe) - the only difference is that a real image is located in a region in space you can touch, i.e. you can put your hand where the image is forming.

A virtual image is an imaginary object that appears as if the rays of light you are seeing are originating from it.

The good example is a mirror hung on a wall. The light rays reflected from the mirror are such that they seem to originate from a region inside the wall, but you realize that there is no such region - they just appear that way.

On the other hand, a projector (like in the cinema) it a good example of a very real image you can 'touch'.

  • $\begingroup$ So it sounds like the virtual image itself is not necessarily the cause of any curving in my example. Perhaps this is specific to a spherical surface then... $\endgroup$ – g3cko Apr 10 '18 at 18:01
  • $\begingroup$ I assume that by curved you mean it's distorted. Distortion is one of a few primary aberrations of an image that are unavoidable when imaging with spherical or cylindrical lenses. Anyway, there's no preferred image for distortion to take effect. Real and virtual images can be distorted and prettry much the same manner. $\endgroup$ – Yuval Weissler Apr 11 '18 at 4:45
  • $\begingroup$ "Also note that the virtual image is curved. Since the dome is spherically symmetric, every object at infinity will produce a virtual image at the same distance from the dome, regardless of the object's direction. Hence, 'infinity' is mapped onto a sphere that is concentric with the dome but has a larger radius. Extended objects that are closer than infinity produce virtual images that are more flattened, but still wrapped onto a curved surface." -- this is the specific quote from the link above. Perhaps "distorted" is the better phrase? $\endgroup$ – g3cko Apr 11 '18 at 5:36
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    $\begingroup$ Yep. You search and read about optical distortion. $\endgroup$ – Yuval Weissler Apr 11 '18 at 6:24

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