Re: Eyepiece and virtual image

Posted by Aryeh Weiss on
URL: http://confocal-microscopy-list.275.s1.nabble.com/PSF-with-DIC-tp3781952p3787390.html

Try removing the ocular and repeating the test. I think that you will
see the same image on your paper, except it may be brighter. The very
small depth of focus of your objective translates into a very large
image depth. There ia table that shows this at:
http://www.microscopyu.com/articles/formulas/formulasfielddepth.html

It may be that on your paper, you are seeing an undeviated component of
the real image from the objective/tube lens combination, which passed
though the center of your ocular. If I am correct, then you will not see
a very sharp image if you use a low mag/low NA objective, and you will
see the best images with high mag/high NA objectives.

--aryeh

Joachim Hehl wrote:

> I would say it is in focus. But yes it gets a bit sharper when adjusting
> the focus. And the wider I go back with the paper the bigger the image
> is, like a projector.  Maybe you try it out with one of your scopes?
>
> Joachim
>
> On [DATE], "Guy Cox" <[ADDRESS]> wrote:
>
>     But is this image truly in focus?  If you adjust the microscope
>     focus, does it get sharper?
>
>                                                                   Guy
>
>
>     ------------------------------------------------------------------------
>     *From:* Confocal Microscopy List
>     [mailto:[hidden email]] *On Behalf Of *Joachim Hehl
>     *Sent:* Thursday, 8 October 2009 8:03 PM
>     *To:* [hidden email]
>     *Subject:* Re: Eyepiece and virtual image
>
>     Dear Guy,
>     The point is that I neither adjust the focus nor lift the eyepiece.
>     I look through the eyepiece (without my glasses, I am
>     short-sighted), focusing and then I only hold a piece of paper in
>     front of the eyepiece and can see the picture on it. And this also
>      happens  to my normal-sighted colleagues.
>     Joachim
>
>     On [DATE], "Guy Cox" <[ADDRESS]> wrote:
>
>         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
>         ______________________________________________
>         Associate  Professor Guy Cox, MA, DPhil(Oxon)
>         Electron Microscope Unit, Madsen  Building F09,
>         University of Sydney, NSW  2006
>         ______________________________________________
>         Phone [phone]     Fax [phone]
>         Mobile [phone]
>         ______________________________________________
>              http://www.guycox.net <http://www.guycox.net/>  
>
>          
>
>          
>         ------------------------------------------------------------------------
>         *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
>
>         Web: www.lmc.ethz.ch
>         Phone:     [phone]
>         Natel:     [phone]
>         Fax:        [phone]
>         e-mail: [hidden email]
>
>
>

--
Aryeh Weiss
School of Engineering
Bar Ilan University
Ramat Gan 52900 Israel

Ph:  972-3-5317638
FAX: [phone]