CD solar spectroscope?

[GeoffMc (Geoff)]

Hi All,

I'm in the process of writing a high school (Year 11/12) teaching unit on the Sun, with the emphasis on observing and experimenting rather than looking up images. Is it possible for school students to see absorption lines reasonably well using a CD spectroscope? I've tried making one with no success (at seeing the lines): just a bright, glaring image surrounded by continuous spectra. Nothing like the images on the net. Any ideas would be helpful.

Thanks,

Geoff Mc

[Merlin66 (Ken)]

Geoff,
There's a chapter on CD/DVD spectroscopes in Tonkin's "Practical Amateur Spectroscopy" - I'll have a look later...
I think the resolution is pretty low and the absorption lines may be difficult to record.
A reflective needle and a cheap "students" grating may be an easier way to go...

[batema (Mark)]

I am also a high school teacher and have students doing investigations into spectroscopy. Is there any way to produce a spectrum of a star that may show spectral lines for a relatively cheap outlay. I have seen where you can print off a diffraction grating and put it onto an Overhead Transperancy that can be put over the front of a telescope. of course I can not find where my mate told me to look for this. Any suggestions.

Mark

[Merlin66 (Ken)]

Unless the design (and your printer) can give at least 100 lines/ mm - then all you have is a glorified Ronchi screen. The resolution will be very poor.
IMHO the easiest and fastest way is either a good prism infront of a telelens (say 135mm etc) or one of the P-H student gratings and use either the needle trick or mount a pencil sharpener slit in the end of a tube/ box about 1400mm long - use a mirror if necessary to shine the sunlight onto the slit and image it with a grating on the front of the lens.
This will definately show the Fraunhofer and Telluric (Atmosphere) lines etc etc. The set up can also be used to show the spectra from various lamps (Flouro/ Neon/ Incandecent etc) as well as the effects of various filters....Some neat projects there....

[robz (Robert)]

Geoff, see my post on Merlin66''s thread : ''SOLAR SPECTRUM WITH BAADER GRATING''

Rob.

[GeoffMc (Geoff)]

Thanks Rob and others. I made a spectroscope using a DVD with similar dimensions to the one Rob described on another thread, using a cereal box and closely spaced masking tape (~0.2mm slit). I cannot seem to get the hang of seeing anything other than a continuous spectrum. No lines are visible. Any ideas?

Geoff Mc

[robz (Robert)]

Hi Geoff, did you split the DVD in half?
I usually cut it down the middle, twist it a bit and begin to carefully pull apart the two halves(remember DVD's are dual layer, even the blank ones).
If you do this carefully you should be able to cut a decent pie wedge from a part that isn't damaged(which happens)

Now, your continuous spectrum : happened to me also.
I realised that for some reason the ''higher order'' spectrum(to the right of the main one was where all the detail was???......that was with a CD though.

When I replaced the CD wedge with a DVD wedge, I mucked around with the angle of the wedge while looking through the view hole and suddenly, there it was............bright and detailed. The image was more to the wide, top end(closer to the view hole) of the wedge.

A couple of things to check: the wedge has to be cut from the CD as you would a ''pie''.
That wedge is mounted directly under the view hole with the wide end at the top and the small end stuck down in to the tube.

The position and angle of that wedge of DVD is important and you may need to fiddle with it a few times.
Also, the slit must be horizontal, NOT vertical in relation to the wedge and view hole.

Keep trying mate............it's a bit fiddly, and a P.I.T.A., but you should see the detail sooner or later. Keep moving your wedge and your eye around and it will pop in to view.

Good luck.

Rob.

[GeoffMc (Geoff)]

Thanks Rob. I'll give it another try.

I spoke to a uni technical officer yesterday, a particularly smart and very experienced physicist with a very practical approach, and he was doubtful that absorption lines could be seen in solar spectra. If I'm successful, he will be particularly pleased.

I'll let you know how it goes.

Cheers,

Geoff Mc

[robz (Robert)]

Originally Posted by Geoff Mc

Thanks Rob. I'll give it another try.

I spoke to a uni technical officer yesterday, a particularly smart and very experienced physicist with a very practical approach, and he was doubtful that absorption lines could be seen in solar spectra. If I'm successful, he will be particularly pleased.

I'll let you know how it goes.

Cheers,

Geoff Mc

Can't argue with an educated and fully qualified physicist can we? :

http://www.cs.cmu.edu/~zhuxj/astro/h...ctrometer.html

Also, see my new photos on the other thread.

[GeoffMc (Geoff)]

Hi Rob,

don't misunderstand my comment about the physicist: like most I know, he will definitely and genuinely be pleased to learn something new. He is a very fine teacher and is always open to new ideas and willing to learn. That's why he's so good at what he does.

I have seen the website you suggested and this is the design I made up the other day. I could not see the absorption lines, however. I'll try again. I assume the secondary spectrum is the one to look at? The primary is too glaring to see anything. Should I use reflected light? Do I focus on infinity or on the CD?

Thanks,

Geoff Mc

[robz (Robert)]

Geoff, I replaced the DVD wedge with a CD wedge instead.

The design shown has an angle of 60 degrees which is way out compared to my version.
I have an approximate angle which looks more like 30 degrees.

While experimenting with the angle of the CD/DVD, I noticed that the spectra(and the dark lines!) can be blurred and distorted if the angle is not right on!

Also, the viewing hole is about 12mm diameter, not a huge chunky opening like the design indicates........the interior image needs darkness!

Yes, you need to use reflected light : off a white painted building/sheet/paper or similar.

You should be able to see in the reflection on the CD, with your eye right up against the viewing hole(like an eyepeice), the primary spectra to the left, and a fainter secondary spectra to the right.
You might need to move your eye slightly to the left and right to see these.
It's hard to tell whether the focus is at infinity or not. I had my camera set to normal and macro........both worked.......so it seems?
I would imagine that the focus point would be the slit itself.................someone correct me if I'm wrong.


Please show your physicist freind the photos below:
All taken with a DVD as a grating!

[robz (Robert)]

Merlin66.....................any comments or input on this?

[GeoffMc (Geoff)]

Hi Rob,

I've just finished making a spectroscope following your advice and the result, at least for artificial light sources, is far superior to the version using a box I've tried before. On incandescent bulbs there is a continuous spectrum, but on fluoro tubes and compact fluorescent bulbs, there are several bright lines. I assume these are the emission lines specific to this design of light? Unfortunately, I will have to wait until tomorrow to check out the Sun. Can't wait.

Ironically, this is the first time I can remember wanting the night to end!

Cheers,

Geoff Mc

p.s. Here is another site that shows the construction quite well.
teacher.edmonds.wednet.edu/edmondswoodway/.../cd-dvd_spectroscope.pdf

[Merlin66 (Ken)]

Sorry guys...caught up rebuilding an observatory!
The CD has about 600 l/mm (equivalent) (PAS, Chapter 5)
They recommend using it at a grazing angle of around 3 degrees, with the camera lens (50mm fl) almost touching the surface of the disk. Focused on infinity.
When the CD is used with a slit - the camera should be focused on the slit.
EDIT: Should add that the 2nd order spectrum sits about 20 degrees from the surface (based on 3 degree incoming); 1st order about 40 degrees.

[Merlin66 (Ken)]

If you're using a Neon or a Fluoro lamp for testing, Christian Buil has a fully annotated spectrum of both on his website:
http://astrosurf.com/buil/us/spe2/hresol4.htm

[robz (Robert)]

Thanks Merlin.
It's all a bit technical still for me, but I'm beginning to understand....slowly.
What is ''PAS chapter5''?

Also, what do you think about the photos Merlin?

Geoff, .......congrats mate!........you're nearly there by the sounds of it!

Cheers,
Rob

[Merlin66 (Ken)]

PAS - Practical Amateur Spectroscopy - Ed. Steve Tonkins
I think the images may be slightly out of focus, but I'll try to load them into Vspec - see if we can pull some data....

[robz (Robert)]

Great Merlin.

I noticed that the images on this thread can not be enlarged

On your solar spectrum thread, they can.

If you are going to closely examine the photos, it would be better to use those and not the ones here.

Quite possible that a couple of the shots have poor focus due to the ''autofocus'' function that can not be overidden on a standard digital camera.
From as far as I could tell, the camera was trying to focus on the slit

Anyhow, please let us know what eventuates.

Cheers,
Rob.

[Zaps]

Hi Merlin. One of the two Amazon reviews of Tonkin's Practical Amateur Spectroscopy claims the book is riddled with errors and misprints, etc, and recommends that propective purchasers wait for a corrected edition. Care to comment?

[Rob_K]

Don't know if this might be of interest:
http://www.stargazing.net/david/spec...ctroscope.html

Cheers -