Re: Eyepiece and virtual image

Posted by Guy Cox on
URL: http://confocal-microscopy-list.275.s1.nabble.com/PSF-with-DIC-tp3781952p3786986.html

You can always get a real image from an eyepiece by refocussing so that the first image is in front of the focal plane of the eyepiece - either adjust the microscope focus a little or lift the eyepiece slightly in its tube.  If you see a sharp image without refocussing from your normal viewing position, it probably means that you - like me - are long-sighted!

 

                                                                    Guy

 

Optical Imaging Techniques in Cell Biology
by Guy Cox    CRC Press / Taylor & Francis
    http://www.guycox.com/optical.htm
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Associate Professor Guy Cox, MA, DPhil(Oxon)
Electron Microscope Unit, Madsen Building F09,
University of Sydney, NSW 2006
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From: Confocal Microscopy List [mailto:[hidden email]] On Behalf Of Joachim Hehl
Sent: Thursday, 8 October 2009 7:36 PM
To: [hidden email]
Subject: Eyepiece and virtual image

Dear all,

I have a –maybe stupid- and not confocal but “basic optic” question:

As you can read in all textbooks concerning microscopy and geometric optics the objective produces a real, inverted and magnified image since the distance from the object to the object front lens is bigger than one but less than two focal lengths of that given objective.
This intermediate image is then  magnified by the eyepiece. Since the intermediate image lies exactly in the front focal plane of the eyepiece the result is a virtual, true sided and magnified image which occur in the infinite space.  Our eye with its optical components is then producing a real image on the retina.
So far, so good.
By definition, a virtual image can not be captured on a screen. BUT: When I hold a piece of paper in front of the eyepiece in a distance bigger or smaller than the  back focal plane of the eyepiece (the distance I use when I look through it with my eyes) I am able to capture a pretty sharp image of my object on the paper. Why is this? I should not since it is a virtual image?
Thanks for your input!

Joachim


Joachim Hehl
LMC-Light Microscopy Centre, ETH Zurich Hönggerberg
Schafmattstrasse 18, HPM F16.1
CH-8093, Zurich, Switzerland

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