Cheap spectroscope ?

robz (Robert) · #1 18-02-2011, 07:01 PM

Hi guys.
Just a quick question as I can't spend any considerable amount of money on a star spectroscope a la ''L200'' or ''Rainbow Optics'', ''Star Analyser'' etc.

I've found myself playing with blank DVD's, CD's both reflective and transmissive (with aluminium backing removed)
Some interesting results, but transmissive (as in Rainbow Optics)does not seem to provide a close to the source spectra that's bright enough??

Any ideas on a cheap way to be able to directly view some star spectra using DVD's or CD's?
Help appreciated

Merlin66 (Ken) · #2 18-02-2011, 07:23 PM

Great to play with and demonstrate diffraction....
You can get a solar spectrum from the reflection....
In Tonkin's "Practical Amateur Spectroscopy" there's a chapter on setting up both the CD and the DVD disks to obtain spectra.
IMHO they're of limited value for any scientific measurements.
(Google CD spectroscope...plenty of links there)

A Paton Hawksley 100 l/mm grating which comes mounted in a 35mm film frame is better but then you face the issues of fitting it.
OK as an objective grating (mounted in the lens hood of a standard lens on your DSLR) but a bit more difficult to fit to the scope.
I have some telescope mounting frame designs available over on the Y! group astronomical_spectroscopy forum.
Hope this helps....

robz (Robert) · #3 18-02-2011, 10:39 PM

Thanks Merlin, I'll check them out and do some research.

Regards,
Rob.

higginsdj · #4 19-02-2011, 10:06 AM

You can also buy cheap holographic transmission grating material from Edmund Optics. It was something like $20 per sheet or you could buy it mounted int 35mm slide frames.

robz (Robert) · #5 22-02-2011, 03:05 PM

Thanks higginsdj.

I was thinking more along the line of reflective gratings rather than transmissive, hence my DVD/CD idea.

BTW, where are you guys getting this L200 thingy?........and how much does it cost?

I've looked back on some posts but haven't found much..............have I missed it?

higginsdj · #6 22-02-2011, 03:14 PM

We've been posting on the astronomical_spectroscopy yahoogroup (owned by Ken I believe)

I'm 80% through construction/setting up my L200 and will likely start calibrating/adjusting soon. Got to wait for my new CCD camera before making any permanent changes. The unit cost ~$900 AU. Not sure if Ken has any left.

Cheers

Merlin66 (Ken) · #7 23-02-2011, 02:53 AM

The Spectra-L200 Littrow spectroscope Kit was designed and developed to assist amateur astronomers get into serious spectroscopy at a reasonable price.
It is only available to members of the Y!group astronomical_spectroscopy. There are currently three in Australia.

robz (Robert) · #8 23-02-2011, 01:39 PM

Thanks everyone, but it's too much money for me at the moment.
May have to go for the Rainbow Optics gratings for the time being by the looks of it.

Merlin66 (Ken) · #9 23-02-2011, 01:42 PM

I believe that Rainbow Optics are no longer shipping outside the US.
That leaves the P-H Star Analyser....

robz (Robert) · #10 23-02-2011, 03:22 PM

Quote:

Originally Posted by Merlin66

I believe that Rainbow Optics are no longer shipping outside the US.
That leaves the P-H Star Analyser....

Damn!..........I see.............

robz (Robert) · #11 24-02-2011, 02:13 PM

Merlin and all..................had a read of Merlin's ''classic spectroscope '' article and started toying around with a few bits and peices I had lying around the house.

Used a tungsten lamp with a small slit cut into a cardboard mask covering the lamp.
Then placed a 35mm slide projector lens (backwards) as a collimator.
Propped up a cd verically against a small cardboard box (poor man's grating

).
Grabbed a Tamron 28 - 200 mm camera lens (ex 35mm film camera)and set it to 200mm and focussed at infinity.The aperture looked open fully as far as I could tell(designed to be used with a fully automatic SLR camera)
Viewing was done with a 25mm eyepeice.

After some fiddling and angling the cd around, I managed now and then to focus (I think?) on the spectrum image entering through the camera lens. So, in theory,my crude system works, but how well with a CD or DVD grating, I don't really know.

It was getting late and I didn't get the opportunity to try a mercury based light source which would have provided some more definitive answers on the results.

Rob.

Merlin66 (Ken) · #12 24-02-2011, 02:25 PM

Rob,
That's all good fun and shows what can be done...
With the lenses you already have all you really need is a small reflection grating say 300 l/mm and you'd get some VERY nice results!!
Keep it going....

robz (Robert) · #13 24-02-2011, 05:10 PM

Will do Merlin!

Having a ball with this

Will be looking around for a proper grating as you suggest and who knows............may get a working star spectroscope............something I've allways wanted to do!

I'll report on what transpires at a later date.

Cheers,

Rob.

higginsdj · #14 26-02-2011, 11:06 AM

You know, I think this is my downfall in this hobby. I love tinkering (building things) but I hate setup (if it doesn't work right off I lose my patience) and my real passion is doing something with the data. Its that middle bit that drives me to distraction.....

Robert I applaude you for your patience

Cheers

David

robz (Robert) · #15 27-02-2011, 10:31 PM

.....David, many thanks, but trust me I'm not that much different to you

.

Set up is the worst part no doubt, and I have lost it(patience) many times in various projects

.

In nearly every case though, I've slapped myself on the wrist for being such an idiot and gone back to the problem at hand..........some more swearing and cursing and then it finally comes together

Today I popped in to the local Cash Converters store and picked up a compact lightweight 28-200 Tokina camera lens.........perfect for this spectroscope project (half the size and weight of the Tamron I have been fiddling with)...........how much?............$19.00 !!!!!!

I can only give one tip : never let anything beat you too easily.In most cases you are so close that you don't even know it until it dawns on you - days, weeks or even months later............such is D.I.Y

Cheers!

Rob.

Merlin66 (Ken) · #16 27-02-2011, 10:35 PM

Re CD and DVD gratings....
I just noticed on a bulk stack of CD's I bought that there's a "spare" clear protective CD at the top of the stack...it looks as if it has the same groove pattern as the other CD's but is transparent. May be worth checking out...you could use a dremmel tool to cut a 28m filter sized disk...

robz (Robert) · #17 28-02-2011, 02:33 PM

Yes, I've noticed and thought about these also

In regards to a DVD as opposed to a CD, the DVD when cut,firstly in half, actually delaminates in to TWO DISCS (dual layer)
From half of that DVD comes a thin and quite bright grating(reflective) and one clear grating..........how good it is to a CD or non delaminated DVD is not as yet known.

Initial tests easily reveal spectrra from bright street lamps and fluro house lighting..............and this is from a CD or DVD!!!

Some trivia : CD = 600+ lines per mm, DVD = 1300+ lines per mm.

Merlin66, any suggestions on which will be better - CD or DVD ?

Cheers,
Rob.

Merlin66 (Ken) · #18 28-02-2011, 05:35 PM

IMHO I'd start with the CD - the deviation angle is less and the dispersion wide enough to collect useful spectra - if it works.

theodog (Jeff) · #19 28-02-2011, 07:09 PM

Hi Rob,
Try this site.
http://www.amnh.org/education/resour...ectroscope.pdf

It may provide a template for a more substantial s.scope made of cardboard or ply.
I have made several of these with my students and it suprises them how much detail can be seen of energy saver lights.
I have even hand-held a 'happy snap' ccd camera to image the spectra seen.

I have posted about this 'paper spectroscope' here before, but can not find it.

robz (Robert) · #20 01-03-2011, 03:19 PM

Merlin, Jeff, I have used the CD in the cardboard box/viewer arrangement and yes, ............it works!..........no problem at all.

It seems that the ''REFLECTIVE GRATING'' method is the preferred as directly placing a stripped/clear cd or dvd over the eyepeice does not seem to work..........even on a bright star like Sirius