0
$\begingroup$

I am near-sighted. Here is the phenomenon: I stand in front of a light source that is situated on the ceiling so that it reflects off my eyeglass lenses and appears circular. It is a white light source but appears shifted a blue-green in the reflection. When I tilt my head so the reflection is in the very corner of the lens, the circle becomes dramatically oval-shaped and the color has shifted. On the side closest the edge it is red and on the more medial side, blue. First, why is the reflected image (no head tilt) green? Second, why does the image shift in color when situated on the edges? I am guessing the thickness of the lens has a role to play, being thicker on the edges but I don't know how to explain all of it. I'm am guessing also as I tilt my head the angle may hit a critical point where it acts like a prism where you can get all the colors out. Again just speculating here though

$\endgroup$
  • $\begingroup$ I think that oval shaped circle is due to the change in curvature of the lens. Also, the changes in the spectral colours observed may be due to the changes in the relative refractive indices of different parts of the lens. $\endgroup$ – Shishir Maharana Aug 5 at 3:48
0
$\begingroup$

Probably the colors are due to an antireflection coating or UV rejection coating on your lenses. Those shift color with the angle of reflection.

You are right that the oval shape of the reflected image of a circle is due to curvature of the lens. If you look at the reflections in, e.g., a christmas tree ball or fishbowl, you wiĺl see a similar effect ( though not the color shift). To see a similar color shift, you could look at reflections in good quality camera lenses or binocular lenses.

$\endgroup$
  • $\begingroup$ I guess in a christamas tree ball (red one for example) there'd be a drastic color 'shift' ? ;) $\endgroup$ – DakkVader Aug 5 at 6:39
  • 1
    $\begingroup$ Yes, except that the color would not change with angle. However, if the color is due to multilayer interference (as in the case of oil on water or thin coatings on glass) the reflected color is a function of angle. $\endgroup$ – S. McGrew Aug 5 at 12:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.