How Do Telescopes Magnify? School Level.
W. eWatson
diagrams. No equations. I'd like to use it for 6-10th graders and some
lay people. From my physics books long ago, they would show an object
that passes through a lens (objective), and then into and out of an
eyepiece. Each stage would show the object as a vertical line (usually)
at various heights. I want to give this to some educators in about 2
hours who are conducting a class on telescopes. They seem baffled by the
idea. Well, if not at this time, then in a future week. By then I'll
probably have time to describe it to them.
I'm on Google looking, but nothing like what I want seems to be available.
OG
"W. eWatson" <wolft...@invalid.com> wrote in message
news:hgbi21$k98$1...@news.eternal-september.org...
Does it have to be a diagram?
Can you just get a long focal length lens and use it to form an image on a
piece of tracing paper.
The get a short focus lens and use it to magnify the tracing paper image.
You can then remove the tissue paper and show that you have really made a
telescope!
Gil
That is an excellent idea, and will illustrate the idea perfectly.
Quadibloc
> I'm looking for a good description of how telescopes magnify using
> diagrams.
On my own web page, at
http://www.quadibloc.com/science/opt01.htm
you may find something helpful.
John Savard
Joseph Mack
>
>> I'm looking for a good description of how telescopes magnify
> Does it have to be a diagram?
>
> Can you just get a long focal length lens and use it to form an image on
> a piece of tracing paper.
> The get a short focus lens and use it to magnify the tracing paper image.
>
> You can then remove the tissue paper and show that you have really made
> a telescope!
I like the practical approach to education too.
However telescopes don't magnify the image. The sun is about a million
miles in diam and in a telescope the image is about 1cm. A telescope
reduces the size of the object. What it does that we want is increase
the angular size of the image subtended at the eye over that of the object.
Joe
--
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!
Helpful person
> However telescopes don't magnify the image. The sun is about a million
> miles in diam and in a telescope the image is about 1cm. A telescope
> reduces the size of the object. What it does that we want is increase
> the angular size of the image subtended at the eye over that of the object.
>
> Joe
>
image are at infinity. The magnification is angular.
canopus56
Lens Combinations: Telescopes (click the hyperlink "astronomical
telescope" in the text).
http://www.mtholyoke.edu/
~mpeterso/classes/phys301/geomopti/twolenses.html
Exploratorium activity - How to make a telescope
http://www.exploratorium.edu/exploring/space/activity.html
A series of handouts I put together in 2006 for this purpose. Includes
online resource references.
http://fisherka.csolutionshosting.net/astronote/astromath/htmatkit/MakeT
elesProject.html
These demonstrations work best with a bag of cheap lenses, eyeglasses,
hand-held magnifying glasses and/or a small make-up mirror as opposed to
ray tracing diagrams. You can use a two-hand held magnifiers, a hand-
held magnifier and a telescope eyepiece.
- Canopus56
Quadibloc
> OG wrote:
> > Can you just get a long focal length lens and use it to form an image on
> > a piece of tracing paper.
> > The get a short focus lens and use it to magnify the tracing paper image.
>
> > You can then remove the tissue paper and show that you have really made
> > a telescope!
>
> I like the practical approach to education too.
>
> However telescopes don't magnify the image. The sun is about a million
> miles in diam and in a telescope the image is about 1cm. A telescope
> reduces the size of the object. What it does that we want is increase
> the angular size of the image subtended at the eye over that of the object.
Telescopes _do_ magnify _an_ image. The telescope - or, rather, the
*eyepiece* - magnifies the virtual image of the object formed by the
objective lens. This allows the eye to focus on that image while
getting a larger angular size...
John Savard
dke...@hotmail.com
Hi
Most of the suggestions jump right into
ray tracing with lenses. I think that isn't
really what you want to do.
Here is my suggestion:
1. Start with a pinhole projection. A real
demonstration is best here. This demonstrates
the concepts of projected image size, intensity
loss and ray tracing.
2. Bending light with glass. Best if done with
a block of glass and showing a beam traced through
the block.
3. Show how a lens is like a lot of pinholes that
bend the light depending on where the light goes
through the lens. Show focal point.
4. Show how the eyepiece is like a magnifying glass
to look closer at the projected image.
Dwight
OG
"Joseph Mack" <jm...@wm7d.net> wrote in message
news:hgc59s$rp$1...@news.eternal-september.org...
> OG wrote:
>>
>
>>> I'm looking for a good description of how telescopes magnify
>
>
>> Does it have to be a diagram?
>>
>> Can you just get a long focal length lens and use it to form an image on
>> a piece of tracing paper.
>> The get a short focus lens and use it to magnify the tracing paper image.
>>
>> You can then remove the tissue paper and show that you have really made a
>> telescope!
>
> I like the practical approach to education too.
>
> However telescopes don't magnify the image. The sun is about a million
> miles in diam and in a telescope the image is about 1cm. A telescope
> reduces the size of the object. What it does that we want is increase the
> angular size of the image subtended at the eye over that of the object.
>
You would do well to set up the demonstration and actually see how it works.
The eyepiece operates exactly like a magnifying glass on the image produced
by the objective lens. A long focal length objective gives a larger primary
image, and a shorter focal length eyepiece gives greater magnification of
the primary image.
OG
Surely in an astronomical telescope the image produced by the objective
is a *real* image rather than a *virtual* image - which is why it can be
seen on the tracing paper.
Martin Brown
> I'm looking for a good description of how telescopes magnify using
> diagrams. No equations.
OK. Do you know the classical constructions for drawing a scaled ray
trace diagram? That is one way to proceed without equations.
The problem is that your audience might just about understand it at the
time but would never be able to reproduce it for their class.
> I'd like to use it for 6-10th graders and some
No idea how old that makes them.
> lay people. From my physics books long ago, they would show an object
> that passes through a lens (objective), and then into and out of an
> eyepiece. Each stage would show the object as a vertical line (usually)
> at various heights. I want to give this to some educators in about 2
> hours who are conducting a class on telescopes. They seem baffled by the
> idea. Well, if not at this time, then in a future week. By then I'll
> probably have time to describe it to them.
>
> I'm on Google looking, but nothing like what I want seems to be available.
If you can slightly change the topic to microscopes and magnifying
glasses then they are a *lot* easier to explain to a lay audience.
And in a very real sense a telescope objective is just a light
collecting device that creates an image at its focal plane for an
eyepiece to look at. Choose the eyepiece and alter the magnification.
You can do some very simple demos of how the lens curvature affects the
magnification since cheap 3" magnifying glasses, crystal balls and clear
marbles are cheap and easily obtainable. Looking at fabric with them
reproduces how exactly linen makers first got into the game. If you are
feeling really daring making a crude high power spherical lens for a
Leeuwenhoek microscope is well within the bounds of what a school lab
can do. Image may be a bit ropey unless you are *very* good at it.
Chromatic aberration will be awful but you can show the general
principles without expensive components or a collimated light source.
Regards,
Martin Brown
Quadibloc
wrote:
> W. eWatson wrote:
> > I'd like to use it for 6-10th graders and some
>
> No idea how old that makes them.
First graders are students who have just entered school, so they're
usually 6 years old.
That makes a typical 6th grader 11 years old, and a typical 10th
grader 15 years old.
John Savard
wsne...@hotmail.com
Project an image onto a screen using a suitable objective lens. Allow
participants to view that scene with a magnifier.
Using a similar objective lens allow the participants to look through
a similar magnifier, but this time straight through, without the
screen. They can compare the general similarity of the images seen.
AM
Hi.
Speaking from experience here.
For typical kid's that age, I go out of my way not to
use numbers and technical *speak* as much as possible
when demonstrating how a refractor or reflector works.
I use the GalileoScope, and CI FirstScope Newtonian
and show them how an image is formed. And just a basic
introduction to focal length and focal ratio. Both
the scopes are excellent in giving them the basic idea.
My reasoning is simple. I want to get them interested and
if interested enough, they will go out and find more
information on their OWN. Which to me is the most important
part. The key thing is to get the spark going in them.
From 6 - 14 yrs old, the numbers bore them quickly. And
from 15 - 18 you are competing with cars, girls and the
like. So again, most important is to surprise them, and
show them how easy it is for them to get involved and
figure things out for their own. Those who really want
more information will always ask, or contact teachers
and or look on the web for more. Having info materials
handy to pass out works well there.
I've been doing outreaches for many years now, (I'm now
the club outreach coordinator) and from experience this
is what works best.
I tried the IAU presentation (s) and found them to literally
put kid's to sleep. Hence I made my own, and they have been
a great success. Showing them what they can do FOR astronomy
like variable star, and double star observing, imaging and
mirror making seem to get their attention the best !
Getting them hooked on astronomy is the most basic and
important thing IMHO. The rest is easy after that...
"Give A Man A Fish You Feed Him For A Day
Teach A Man To Fish You Feed Him For Life"
This approach seems to work best for people of all ages.
--
AM
W. eWatson
I think you are close to the answer. To illustrate how it magnifies, one
needs a diagram that shows how the eye sees an object without any
lenses. That is, what is the angular size of the object. Next show how
the angular size changes by using lenses.
Another way would be to do a comparison with a two lens system. Keep the
objective focal length the same. Show the size of the projected image on
a wall in each case where the focal length of the second lens is 1/2 or
1/3 of the first.
W. eWatson
Note surround long links with <>. It prevents wrapping.
<http://fisherka.csolutionshosting.net/astronote/astromath/htmatkit/MakeTelesProject.html>
W. eWatson
touches upon simple numbers and mathematics. In the chapter titled A
Story About Numbers he makes the interesting comment that we relate much
more strongly to stories than numbers. However, this can be to our
peril. This is not necessarily true on the subject here, but there are
times when we need to deal with the numbers and not the story.
He illustrates this very clearly in the controversy of breast implants
back in the early 90s causing breast cancer. The public wanted to hear
the story, but the real story was in the numbers (data). It took over a
decade to reverse the idea that the implants produced cancer. He again
illustrates the problem with a couple of very simple questions involving
numbers. About 90% of people answer incorrectly. With a simple
application of algebra, the correct answer is obvious. Don't hide it all
the time.