Date: Wed Dec 19 14:01:52 2007

Author: Gerald Zani

Subject: Re: Demonstration of optical resolution ?

Post:
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Urs my European friend,

I do a simple demo to show the diffraction effect on resolution.

I mount a 75mm lens onto video camera and place an adjustable aperture in front of the lens but leave it wide open. The lens is focused a small object that is about 30 feet away. For an object I use a piece of paper with the word "RESOLUTION" in small letters printed on it. The letters are illuminated with a light source that has an adjustable intensity. The camera image is projected on a screen where the printed letters are small but visible to the class.

By gradually reducing the aperture on the adjustable pinhole to smaller and smaller size and at the same time gradually increasing the light intensity on the object to keep the brightness constant you can clearly see that the image gets fuzzier and soft when the aperture becomes very, very small.

I know there are other, more accurate ways to show the diffraction limit and resolution tests such as the Rayleigh's Criterion demo and the Airy's Disc demo. But my Professor likes this simple resolution and diffraction demo because it is basic and it appeals to our astronomy class when discussing about diffraction and the resolution of a lens.


We have been getting a lot of snow so far this fall and yet the winter season has not started. Take Care, -- Jerry Z.



At 01:24 PM 12/19/2007, you wrote:
>Hi Taplers,
>
>Re: Urs' remarks seeking a good resolution experiment:
>
>Surely could be a nice component of a modern lab for optics for non-majors.
>They would set digital cameras at various resolutions, photograph objects
>demanding various amounts of resolution and print out and analyze the
>results right in the lab, and b&w would be adequate.
>
>(We "encountered" the resolution variable when revising (to digital) our air
>table collisions experiments with the stroboscope photography. It turned out
>that we had to accept the lowest (or almost the lowest) digital camera
>resolution setting in order that the computer-printer system would operate
>fast enough in the student lab environment - ~30 sec/printed page.)
>
>Bill Norwood
>U of MD
>
>-----Original Message-----
>From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
>Behalf Of Urs Lauterburg
>Sent: Wednesday, December 19, 2007 12:55 PM
>To: tap-l@lists.ncsu.edu
>Subject: [tap-l] Demonstration of optical resolution ?
>
>Dear Tap-lers,
>
>Does anyone of you Taplers do an interesting and instructive demo on
>the theme of optical resolution. Nothing really exiting comes to my
>mind about this but maybe someone else has done or knows something.
>Any shared wisdom is much appreciated. Thanks a lot
>
>and regards
>
>Urs Lauterburg
>
>Physics demonstrator
>Physikalisches Institut
>University of Bern
>Switzerland

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Urs my European friend,
I do a simple demo to show the diffraction effect on
resolution.
I mount a 75mm lens onto video camera and place an adjustable aperture in
front of the lens but leave it wide open. The lens is focused a
small object that is about 30 feet away. For an object I use a
piece of paper with the word "RESOLUTION" in small letters
printed on it. The letters are illuminated with a light source that
has an adjustable intensity. The camera image is projected on a
screen where the printed letters are small but visible to the
class.
By gradually reducing the aperture on the adjustable pinhole to smaller
and smaller size and at the same time gradually increasing the light
intensity on the object to keep the brightness constant you can
clearly see that the image gets fuzzier and soft when the aperture
becomes very, very small.
I know there are other, more accurate ways to show the diffraction limit
and resolution tests such as the Rayleigh's Criterion demo and the Airy's
Disc demo. But my Professor likes this simple resolution and
diffraction demo because it is basic and it appeals to our astronomy
class when discussing about diffraction and the resolution of a
lens.

We have been getting a lot of snow so far this fall and yet the winter
season has not started. Take Care, -- Jerry Z.

At 01:24 PM 12/19/2007, you wrote:
Hi Taplers,
Re: Urs' remarks seeking a good resolution experiment:
Surely could be a nice component of a modern lab for optics for
non-majors.
They would set digital cameras at various resolutions, photograph
objects
demanding various amounts of resolution and print out and analyze
the
results right in the lab, and b&w would be adequate.
(We "encountered" the resolution variable when revising (to
digital) our air
table collisions experiments with the stroboscope photography. It turned
out
that we had to accept the lowest (or almost the lowest) digital
camera
resolution setting in order that the computer-printer system would
operate
fast enough in the student lab environment - ~30 sec/printed
page.)
Bill Norwood
U of MD
-----Original Message-----
From: tap-l-owner@lists.ncsu.edu
[mailto:tap-l-owner@lists.ncsu.edu]
On
Behalf Of Urs Lauterburg
Sent: Wednesday, December 19, 2007 12:55 PM
To: tap-l@lists.ncsu.edu
Subject: [tap-l] Demonstration of optical resolution ?
Dear Tap-lers,
Does anyone of you Taplers do an interesting and instructive demo on

the theme of optical resolution. Nothing really exiting comes to my

mind about this but maybe someone else has done or knows something.

Any shared wisdom is much appreciated. Thanks a lot
and regards
Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern
Switzerland


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