Reversibility of light and returning lens backward

[Eric]

Dear all,

I have quite a naive question but I can't manage to really figure the explanation and even if my assumption is true.

let's suppose you have an object, a lens and the object image ;
with the object at the exact same location if you turn the lens backwards so so frontal face is now the back, will the image be the same as before ?

I presume that for a thin simple lens this is true, but I also guess that it's not true for more complex optical systems which do not behave the same if you return them backwards.

But I also think that the reason why it is so is due to reversibility of light, so that I'm confused because thsi principle should work in both situations wether with a simple thin lens or with a complex systems with multiple elements (like a microscope or a telescope).

Can you help me and tell where I'm wrong ?

Thanks

Fred




--------------= Posted using GrabIt =----------------
------= Binary Usenet downloading made easy =---------
-= Get GrabIt for free from http://www.shemes.com/ =-


---
L'absence de virus dans ce courrier électronique a été vérifiée par le logiciel antivirus Avast.
https://www.avast.com/antivirus

[Lu Wei]

Post by Eric
Dear all,
I have quite a naive question but I can't manage to really figure the
explanation and even if my assumption is true.
let's suppose you have an object, a lens and the object image ; with
the object at the exact same location if you turn the lens backwards
so so frontal face is now the back, will the image be the same as
before ?

Not in the general case.

Post by Eric
I presume that for a thin simple lens this is true, but I also guess
that it's not true for more complex optical systems which do not
behave the same if you return them backwards.

You are right. For complex "thick" systems there is a only special point
(maybe called origin point) by which you can turn the system backwards
and the image remains at the same place.

Post by Eric
But I also think that the reason why it is so is due to reversibility
of light, so that I'm confused because thsi principle should work in
both situations wether with a simple thin lens or with a complex
systems with multiple elements (like a microscope or a telescope).

No, the reason is the symmetry of imaging formula:
1/od + 1/id = 1/f
in which object distance and image distance is exchangeable -- if turned
at the origin point.