🚀 go-pugleaf

On Mon, 13 Aug 2012 17:21:17 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Aug 13, 1:52 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
>> On Mon, 13 Aug 2012 15:01:24 -0700, Mark Borgerson
>>
>> <mborger...@comcast.net> wrote:
>> >In article <labh28dt456903pr8ktglq1du55em53...@4ax.com>,
>> >j...@infinitefactors.org says...
>>
>> >> On Mon, 13 Aug 2012 04:52:24 -0700, Mark Borgerson
>> >> <mborger...@comcast.net> wrote:
>>
>> >> >In article <34je285htmmfscg6643s4qqlqdfjbch...@4ax.com>,
>> >> >j...@infinitefactors.org says...
>>
>> >> >> On Sat, 11 Aug 2012 23:22:35 -0700, I wrote:
>>
>> ><<SNIP>>
>>
>> >> 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.
>>
>> 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- Hide quoted text -
>>
>> - Show quoted text -
>
>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