Re: virtual images and convex lenses

[Robert Cohen <Robert.Cohen@PO-BOX.ESU.EDU>]

> -----Original Message-----
> From: Tim Forth [mailto:tim_forth@HOTMAIL.COM]
> Sent: Thursday, January 03, 2002 5:57 AM
>
> I know that a real image is still formed some distance away
> from the lens,
> but I am wondering about the image I can see _in_ the lens.
> That is, I can
> see an upside down crystal clear image through the lens. Is
> this a real
> image? Apparently not since it appears to be on the other
> side of the glass.
> What causes this?

I think the problem with the setup is that your eye naturally
tries to put the image at the location of something physical.
The image in both cases is not "in the lens" or "at the lens"
but at some point between the lens and your eye.  If the image
is much closer to the lens than your eye (as in the second case
perhaps) it may appear to be "in the lens" but it is not.

What I've used with good success is to place a wire square or
a pencil at the location of the image to provide a reference
for your eye.  It is clear that the image appears to "float" at
the same location as the reference (this can also be used
for virtual images if you are careful).

--------------------------------------------
Robert Cohen           rcohen@po-box.esu.edu
570-422-3428         http://www.esu.edu/~bbq
Department of Physics
East Stroudsburg University
East Stroudsburg, PA  18301
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