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J

Jon Kirwan

Jan 1, 1970
0
Would good ol' Sol be an adequate calibration source? You can
probably look up the daily solar intensity somewhere on the net.
Then you correct for local atmospheric effects. Of course,
if this project has to work in Oregon, it will probably have
to be used only during summer school! ;-)

Oh, and the spectral output is pretty well known and even
includes a few good marker lines.

yeah. See:
http://www.google.com/patents/US5835267

My intent is to only use parts that a student can afford to
buy and OWN at home. Not school equipment. Not access to
expensive tools. Plain, simple, stuff. I have worked out a
folding piece of cardstock paper that makes the box and has
all the right angles set up for them, with baffles (also out
of paper.) The DVD-RW is cheap and is a precision diffraction
grating. The camera is cheap (blister-pack, $10 or less, at
common grocery stores.) The merc-argon bulb is $8 to $12,
depending. That's the ballpark I'm talking about. They build
everything themselves, take it home, and own all of it.

If you come up with a scheme that can align with the sun in a
consistent fashion (without burning their poor eyes out),
get's good data on the sky filtering and effects due to angle
of incidence, uses a stop and baffles in the optical path
that children make by hand using glue and scissors and a
ruler, let me know.

Think 12-year old and up.

Jon
 
J

Jon Kirwan

Jan 1, 1970
0
yeah. See:
http://www.google.com/patents/US5835267

My intent is to only use parts that a student can afford to
buy and OWN at home. Not school equipment. Not access to
expensive tools. Plain, simple, stuff. I have worked out a
folding piece of cardstock paper that makes the box and has
all the right angles set up for them, with baffles (also out
of paper.) The DVD-RW is cheap and is a precision diffraction
grating. The camera is cheap (blister-pack, $10 or less, at
common grocery stores.) The merc-argon bulb is $8 to $12,
depending. That's the ballpark I'm talking about. They build
everything themselves, take it home, and own all of it.

If you come up with a scheme that can align with the sun in a
consistent fashion (without burning their poor eyes out),
get's good data on the sky filtering and effects due to angle
of incidence, uses a stop and baffles in the optical path
that children make by hand using glue and scissors and a
ruler, let me know.

Think 12-year old and up.

What I'm looking for would be analogous to using an ice bath
for temperature calibration. In almost every way, temperature
calibration is difficult. That is, everywhere except for ONE
temperature. And there, it's easy and cheap and any idiot can
do a decent job no matter how clumsy they may be. And single
point temperature calibration is better than nothing at all.

Kind of like that. It needs to be cheap and idiot proof. I'm
not holding my breath. But that doesn't mean I've stopped
looking, either. I just don't think it is in the cards, yet.

Jon
 
G

Geoff

Jan 1, 1970
0
What I'm looking for would be analogous to using an ice
bath for temperature calibration. In almost every way,
temperature calibration is difficult. That is, everywhere
except for ONE temperature. And there, it's easy and cheap
and any idiot can do a decent job no matter how clumsy they
may be. And single point temperature calibration is better
than nothing at all.

Kind of like that. It needs to be cheap and idiot proof.
I'm not holding my breath. But that doesn't mean I've
stopped looking, either. I just don't think it is in the
cards, yet.

Jon

Traceable intensity calibration even to 1%T is not easy. You
could simply aquire some cheap pseudo neutral density filters
such as cheap sunglasses, prefereably with a flat lens, and ask
if you can scan with a local uni's Uv-Vis spectrometer, in
either absorbance or %T mode.

Then armed with a reference, you can do useful %T work. This
assumes using a continuum type source though through your mono.
(If your aim is to analyse the light itself rather than samples
then disregard.)
 
J

Jon Kirwan

Jan 1, 1970
0
OK. What is the final goal as a teaching experience and how will
the difference between 0.1%, 1%, and 10% calibration affect
the learning experience?

1% solar calibration should not be too difficult. Set up
a couple of baffles so that direct sunlight falls on a circle
of known diameter on a piece of white card stock visible to
the spectrometer. The spectrometer looks at this circle of
light and reports a result.

I think 1% will be too difficult that way. I already know how
hard that is to achieve, with good, accurate equipment and
careful procedures. If I get within 1% of NIST as it is, I
consider it very very accurate and very very lucky.

I can't say I know exactly what you are suggesting -- too
many specific possibilities arise in mind. You didn't address
any of my points. So I need to leave it there.

To do an intensity calibration, the students will have to do
a much better job on the entrance slit. I've held off of the
old 'pair of razor blades' idea. (Safety.) But I can
resurrect it if I get in mind something useful to do and it
seems practical.
The alternative is to use your own light source and provide
a sample of known reflectance and spectral characteristics.
After calibration with that standard, the student can examine
leaves, fabrics, minerals, etc, and get a pretty good estimate
of their spectral reflectivity.

The intensity calibration setup I have is rather large right
now and takes up a table. As I said, wavelength calibration
is NOT a problem.

We already use the sun as a source for transmission methods
in a small box. A fluorescent yellow highlighter dipped a few
times into distilled water, kept still transparent clear so
very dilute, produces a beautiful green, for example. It does
require a strong light source to be striking, so that's why
the sun.

DVD-RW is 1350 lines/mm or spaced by 0.74µm. The yellow
spectral doublet of mercury at 577nm and 579nm is very
visible to the eye and a lot of the solar Fraunhofer lines
are also clearly discernable. Which is way better than I'd
expected from cheap DVDs when I started doing this.

Anyway, I will make some thoughts first and then maybe some
attempts regarding the sun (in a few months time) and see
where it takes me. I'll have to consider safety, consistency
regardless of time of year, position of sun in sky, ... and
work out a procedure students can achieve.

Thanks,
Jon
 
J

Jon Kirwan

Jan 1, 1970
0

Yes, $30 is too much and so is requiring a computer. To start
out, the students build a paper box and use a DVD and just
their eyes. The DVD is far far less than $1. (20 cents?) The
box is ONE sheet of cardstock (a few pennies.) The glue is
Elmer's and doesn't need much. That's it. The DVD is the only
tricky part. I just prefer the DVD-RW because it doesn't have
a terrible blind spot in the red band (DVD-R absorbs heavily
over a range in there.)

Some students will then move on to the idea of a camera and
using a computer to process the pixels. There is some work
involved in that next step (I've already written all the
wavelength calibration software, though.) Not all students go
there. Most just stop at the box and use their eyes.
I've been using a piece of DVD-RW grating over the lens of my cell
phone camera as a spectrometer for looking at LED lighting. Not
great, but usable. Most 12 year olds and up have cell phones, usually
with cameras.
<http://www.news.illinois.edu/news/10/1007scheeline_spectrophotometry.html>
Now, getting the picture out of the cell phone camera is another
story.

However, if you want cheap, diffraction grating glasses at $30 for 50
glasses:
<http://www.ebay.com/itm/280806593566>

I'll stick with the DVD-RW. 1350 lines/mm.

Jon
 
J

Jon Kirwan

Jan 1, 1970
0
Yes, $30 is too much and so is requiring a computer. To start
out, the students build a paper box and use a DVD and just
their eyes. The DVD is far far less than $1. (20 cents?) The
box is ONE sheet of cardstock (a few pennies.) The glue is
Elmer's and doesn't need much. That's it. The DVD is the only
tricky part. I just prefer the DVD-RW because it doesn't have
a terrible blind spot in the red band (DVD-R absorbs heavily
over a range in there.)

Some students will then move on to the idea of a camera and
using a computer to process the pixels. There is some work
involved in that next step (I've already written all the
wavelength calibration software, though.) Not all students go
there. Most just stop at the box and use their eyes.

P.S. I also see that the above $30 unit specs "better than
3nm spectral resolution." I'm already getting much better
than that, being able to easily separate 577nm and 579nm
mercury doublet. Easily.

Jon
 
M

Mark Borgerson

Jan 1, 1970
0
What I'm looking for would be analogous to using an ice bath
for temperature calibration. In almost every way, temperature
calibration is difficult. That is, everywhere except for ONE
temperature. And there, it's easy and cheap and any idiot can
do a decent job no matter how clumsy they may be. And single
point temperature calibration is better than nothing at all.

Kind of like that. It needs to be cheap and idiot proof. I'm
not holding my breath. But that doesn't mean I've stopped
looking, either. I just don't think it is in the cards, yet.
OK. What is the final goal as a teaching experience and how will
the difference between 0.1%, 1%, and 10% calibration affect
the learning experience?

1% solar calibration should not be too difficult. Set up
a couple of baffles so that direct sunlight falls on a circle
of known diameter on a piece of white card stock visible to
the spectrometer. The spectrometer looks at this circle of
light and reports a result.

The alternative is to use your own light source and provide
a sample of known reflectance and spectral characteristics.
After calibration with that standard, the student can examine
leaves, fabrics, minerals, etc, and get a pretty good estimate
of their spectral reflectivity.

Mark Borgerson




Mark Borgerson
 
J

Jon Kirwan

Jan 1, 1970
0
Another good experiment might be to make up a chlorophyll
solution---think spinach and rubbing alcohol in a blender,
followed by a paper towel filter. (the paper towel filter
will also produce quite a nice paper chromatogram under the
right circumstances.)

You will see some nice absorbtion spectra for the
chlorophyll and other pigments, you should also see a strong
fluorescence peak in the red when looking at right angles
to the sunlight.

Yup, I also demontrate chlorophyll. I've been writing to
scientists about this for such ideas.

I could post up some pictures, I suppose.

Jon
 
M

Mark Borgerson

Jan 1, 1970
0
We already use the sun as a source for transmission methods
in a small box. A fluorescent yellow highlighter dipped a few
times into distilled water, kept still transparent clear so
very dilute, produces a beautiful green, for example. It does
require a strong light source to be striking, so that's why
the sun.

Another good experiment might be to make up a chlorophyll
solution---think spinach and rubbing alcohol in a blender,
followed by a paper towel filter. (the paper towel filter
will also produce quite a nice paper chromatogram under the
right circumstances.)

You will see some nice absorbtion spectra for the
chlorophyll and other pigments, you should also see a strong
fluorescence peak in the red when looking at right angles
to the sunlight.
DVD-RW is 1350 lines/mm or spaced by 0.74µm. The yellow
spectral doublet of mercury at 577nm and 579nm is very
visible to the eye and a lot of the solar Fraunhofer lines
are also clearly discernable. Which is way better than I'd
expected from cheap DVDs when I started doing this.

Anyway, I will make some thoughts first and then maybe some
attempts regarding the sun (in a few months time) and see
where it takes me. I'll have to consider safety, consistency
regardless of time of year, position of sun in sky, ... and
work out a procedure students can achieve.

Thanks,
Jon

Mark Borgerson
 
J

Jon Kirwan

Jan 1, 1970
0
Hi Jon, I was walking around thinking about your calibration
question.

Seems to me you really want some way to change the angle.

For what purpose?
So here's my 'cheapest' "picnic plate" spectrometer idea.
You go to the store and buy a package of plastic, or Styrofoam picnic
plates. You want some with nice indentations (crenulations) on the
edges. You cut a hole out of the center of one plate, and mount the
grating in the center of the other plate. Place the 'hole' plate over
the 'grating' plate and duct tape the CCD camera to the hole plate.
Camera pointing at grating. Count number of crenulations on border to
measure the angle increment.

Put into my own words, you are using the crenelations as
"angle steps." When I rotate a plate against the other, there
is some force needed to coax it to rotate to the next bump.
So given enough, it divides down the 360 degrees into
something much smaller. Camera would be looking across the
plate towards the grating at the center, I guess.

But what I do now is to just create a nice hardboard box (the
8 1/2" by 11" paper goes into a laser printer, a picture is
printed on it that shows you where to cut and where to fold,
it includes tabs for gluing, and the student simply folds up
a nice box. It includes a place where a cut must be made for
the DVD to be at the perfect angle, and another place where
the slit is to be cut, and finally a last place for the exit
pupil where the dispersed light exits. A short distance away
from that, you place your eye. Or a camera can be placed a
little further away and focused. When you take a picture, ALL
of the visible wavelengths spread out across the image plane
of the camera, so there is no need to rotate the grating
around. It's all captured in a single picture. The software I
have can use that to calibrate the pixel-to-wavelength
formula constants (there are two common formulas used for
this, one polynomial in form, another using sines.) Anyway,
that's about it.

So I'm not sure what the rotation effort would be for. Unless
you were thinking about intensity and something I can't
gather from your words right now.
The whole thing goes in a cardboard box with some sort of
"entrance slit".

Yes, the expanded version goes into a cardboard box with the
camera. Or it can be mounted in a wood box, too.
There must be some cheap consumer item entrance slit.
How 'bout cheap calipers? They even come calibrated!

Well, the way I have done it before is to use two of the old
style razor blades (new, not worn) across an existing opening
where you can move one of them around and lock it down. If
you can keep the slit parallel it's not bad. And by eye, it's
not too complex to do that. A micrometer uses cheap
capacitive methods (sine, cosine in quadrature) to track
motion. I suppose that might be nice to try out, too. They
aren't too expensive (though more than two razor blades.)

Thanks,
Jon
 
M

Mark Borgerson

Jan 1, 1970
0
Yup, I also demontrate chlorophyll. I've been writing to
scientists about this for such ideas.

LOL! Perhaps you should write to the engineers who design the
instruments used by those scientists. Not all of them are regulars on
C.A.E like myself.
I could post up some pictures, I suppose.

That wouuld be cool. I'm about to retire and might have some time to do
more than read and respond on newsgroups.

Mark Borgerson
 
M

Mark Borgerson

Jan 1, 1970
0
Yeah, I noticed that too. His clock is hosed.

Jon

Wierd. I just changed from syncing with time.windows.com to
time.nist.gov, and the time went from UCT to Pacific local.


Mark Borgerson
 
M

Mark Borgerson

Jan 1, 1970
0
Set your clock correctly, idiot.

LOL! I just noticed that my clock is set to UCT. I often do this on
purpose when comparing with data files that we always clock on UCT---it
really helps when you have project files coming from the Gulf of Mexico,
Oregon, 140W on the equator, and 80E in the Indian Ocean. I don't
remember resetting it this time, but perhaps I reset it in an overdose
of Olympic zeal.


Mark Borgerrson
 
M

Mark Borgerson

Jan 1, 1970
0
Yeah, I noticed that too. His clock is hosed.

The maritime museum in Greenwich would beg to disagree!

I do have this computer set to check with an internet time
server, so I'm not sure what is going on here.

Mark Borgerson
 
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