I will try and describe my observations the best I can.
I placed a candle in front of me and my spectacles a bit further ahead of the candle. I have negative power so my spectacles must be concave. I tried to see the image formed from behind the candle and noticed two things :
- There were two images formed, one of them was noticeably further away than the other.
- the image that was further away was green in colour while the original flame was yellow (I believe the technical term is blueshift?)
For the first observation, I came across the concept of a "virtual object" (or as an answer here suggests calling it the "would-have-been image") defined for a convex lens. Using the same logic for a concave lens, I can see why there will two images formed at some distance away from each other. However, I cannot think of any reason for that change in the colour of the second image (A friend suggested Doppler effect but I am thoroughly unconvinced).
Could someone please explain the second observation and correct me if I am wrong about the first one?
A picture of my experiment