I have a few simple questions about lenses;

  1. In convex lenses, an object that is further away from the lense's focal length produces a real and inverted image on the other side of the lens because the light rays cross, right? If I'm understanding this correctly, does the brain essentially flip the image (sorry for my lack of scientific terminology) when the rays cross on/before the retina?

  2. If this is the case (or even if it isn't), why does the image appear to invert when one holds a magnifying glass further away than its focal length? Shouldn't it only appear to invert at all when the object is closer than the focal length?

  3. Building on the last question, why does the image not invert for glasses? Do they not also use convex lenses? I feel like I'm missing something simply but I really can't get my head around it.

Basically, I thought I understood lenses before I realized that if I hold a magnifying glass away from my face, it seems to break all the rules I learned! I have literally spent the last 4 hours researching this and can find nothing. Any explanation would help, and I am really interested in learning.


1 Answer 1


I'll answer your question by order:

  1. Yes, the brain does flip the image that is on the retina.

  2. 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.

  3. 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


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