Re: Numerical aperture and spatial resolution

Posted by Benjamin Smith on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Numerical-aperture-and-spatial-resolution-tp7591293p7591295.html

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The best demo I have found is to make it physically tangible - a demo using
your own hands.  Imagine that the wavelength of your light is the length of
your hand (fingertip to wrist).  That would mean that the base of your
fingers would be a 180° phase shift from your finger tip.  Now rest your
elbows on a table and point your hands in line with your forearms with the
finger tips touching one another.  This is the center of the Airy disk as
the waves are perfectly in phase.  Now, while keeping your elbows in place,
rotate your forearms until your fingertips on one hand reach the base of
the fingers on the other.  The light is now 180° out of phase - this is the
first dark ring (node) of the Airy disk.  Try this with your elbows close
together (small angle = low NA), and elbows wide apart (large angle = high
NA).  You will find you have to move a lot farther to the side to get the
first node with the small angle than the large angle.

Now, technically this demo traces a petzval surface, but the analogy works
well enough to get the point across.  I've even had students do this demo
during tests.

For more visual learners, Paul Falstad's wave applet:
http://falstad.com/ripple/ has a diffraction demo built in.  It also has a
lot of other great demos, including Rayleigh scattering, Mie
scattering/lensing, single vs multimode fiber, holographic gratings,
refraction, etc.  This other wave applet of his is also great:
http://falstad.com/wave2d/  As an added bonus, the site also has a circuit
simulator for when you want to cover CMOS cameras, an animation showing
orbital transitions which is perfect for fluorescence, second harmonic
excitation, and stimulated emission, and a Fourier Transform visualizer
which is perfect for explaining image processing and mode locking in lasers.

Hope this helps,
   Ben Smith

On Sat, Sep 19, 2020 at 2:40 AM F Javier Diez Guerra <[hidden email]>
wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hello,
>
> I wonder if anybody in the list could help.
>
> I want to convey to biology undergraduate students (very allergic to
> physics and mathematics) the understanding of the relationship between
> numerical aperture and spatial resolution.
>
> I have already given them links to the different microscopy primer
> sites. They find difficult to understand why the airy disk is generated
> in the image plane, how the diffraction orders affect resolution and why
> increasing NA reduces the image spot.
>
> Could anybody share a basic and intuitive infographic slide, animation
> or any other resource that could help to ease comprehension in this
> context?
>
> Thanks
>
> Javier
>
>
> --
> Fco. Javier Diez-Guerra, PhD
>
> Servicio de Microscopía Confocal
> Centro de Biologia Molecular Severo Ochoa
> C/ Nicolás Cabrera, 1
> Campus de Cantoblanco
> 28049 Madrid
> SPAIN
>
> Tel     [phone]
> e-mail: [hidden email]
>

--
Benjamin E. Smith, Ph. D.
Imaging Specialist, Vision Science
University of California, Berkeley
195 Life Sciences Addition
Berkeley, CA  94720-3200
Tel  [phone]
Fax [phone]
e-mail: [hidden email]
https://vision.berkeley.edu/faculty/core-grants-nei/core-grant-microscopic-imaging/