Cheap spectroscope ?

[robz]

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:thumbsup:

[Merlin66]

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]

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

Regards,
Rob.

[higginsdj]

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]

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]

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]

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]

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]

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

[robz]

Damn!..........I see.............:sadeyes:

[robz]

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:lol:).
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.:question:

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]

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]

Will do Merlin!

Having a ball with this :thumbsup:
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]

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]

:lol:.....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:rolleyes:.

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 :screwy:

Cheers!

Rob.:)

[Merlin66]

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]

Yes, I've noticed and thought about these also:question:
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]

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]

Hi Rob,
Try this site.
http://www.amnh.org/education/resources/rfl/pdf/du_u03_spectroscope.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]

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 :confused2:

[Merlin66]

Rob,
I could be a combination of the groove shape (when used as a transmission) and the quality/ thickness of the CD.....

[robz]

Thanks Merlin.
So,.........if I'm going to play around with CD's for astronomical spectra, the ''reflective'' method would be the way I presume?

I don't know what type of gratings the R.A and Rigel Systems use, but I've found that the direct view spectra with CD's or DVD's seems to be way off to the edge of the grating and not close to the image of the star.
What is the reason for this I wonder?

[Merlin66]

The Rigel uses a 600 l/mm grating.
The deviation angle ( between the zero order and the spectrum) is roughly 3.8 degrees per 100 l/mm; so for the CD at 630 l/m that's almost 23 degrees and double that again for a DVD.

[Barrykgerdes]

So you want a cheap spectroscope.

Here is a program with instructions to make an effective spectrascope. It was originally supplied by Meade to use with a 416 CCD on a LX series telescope. The program is shareware but you can try it for free. It is compiled basic so may not run on a 64 bit computer but runs OK on my XP.

You will need a CCD camera or similar and a good laser printer that can print the grating onto overhead projector film. I successfully printed out a 200 line/inch grating with a HP 5p laser printer but the overhead paper won't go through through my Konica

Unzip the program read the manual and look at the star spectra

Barry

[robz]

:eyepop:.....................no wonder!!!:rolleyes:
That's an enormous distance/difference.No good as a transmission grating in this case:(

Makes me forget about D.I.Y. and just get the Rigel :confused2:

Is it worth playing around with CD's?
So far, the Edmunds reflective gratings appear very small and VERY expensive.

[robz]

Wow, just saw your post Barry!
Thanks for that!
This will be interesting to say the least. I'll give it a try:thumbsup:

Rob.

[Merlin66]

barry,
At 100 or 200 lines per inch (4 to 8 l/mm) that's a very low line count.
More like a Ronchi grating than a diffraction grating. At 8 l/mm the resolution will be very poor and only macro detail will be observed in the spectrum.
A Cokin B40 "Cosmos" filter would be better, it is a 240 l/mm grating.

[robz]

Oops!................just recalculated and it's NOT that much of a difference:question:

Oh well, something to think about:thanx:

[robz]

Yes...............;)............... .CD reflective grating experiments on table top with small light source are looking very, very good;)

Being an incredibly stubborn and persistant D.I.Y.er, I think I may be on to something here:question:
Going back to the cheap cardboard spectroscope article, I've learnt some important rules on angles, viewing angle amongst other things.

If a crudely made spectroscope (I cheated with an existing small cardboard box) can show a fluro light pin hole spectra, then a star through a telescope should also work............I hope?...........or do I need a slit, collimator, etc.?:help:

[AstroGuy]

Hi Robz,

PM me, I have links to everything you need real cheap (I mean real cheap not shady :) ). I'm not a seller or affiliated with one. Just know of a good supplier.

:thumbsup:

[Merlin66]

As I already mentioned Rainbow Optics don't ship outside the US.

[AstroGuy]

Hi all,

mmmm....I don't know why I did not mention this before:P

I have a thread on a DIY LCD Digital Optical Filter Project in the ATM/DIY section. It uses a LCD screen to filter wavelengths of visible light. The software could incorporate a full spectral scan and in a sense turn it into a digital spectroscopic analyser! If your a little adventurous, you guys should check it out.

[Merlin66]

here's the thread mentioned...
http://www.iceinspace.com.au/forum/showthread.php?t=72640
Astroguy,
I'm interested in your experiments. I'm assuming that a conventional LCD screen is made up from individual pixels which emit either green, red or blue...these are then "combined" (?) through a bayer matrix solution to display any one of the 64 million colours...Is this correct?
If so, a couple of comments:
What's the size of the individual pixel? What's the average distance between centres?
In a DSLR the De-bayering process actually "manufactures" a virtual pixel at the intersections based on the mathematical model used ( Craig Stark has a very good write-up on his site) and it's this "virtual" coloured pixel you see in the viewfinder and RAW image of a DSLR.
I don't know how the individual pixels (if they are only RGB) in a LED can be made to emit a different colour...so it may be a combination of varying intensity for each pixel giving the "impression" of colour ie combined by our eye....
It is certainly possible to easily test the outcome. We have access to spectroscopes with bandwidth resolution of 0.01nm......
How can we help each other???

[Barrykgerdes]

Hi
I am not an expert on displays but there are a number of different ways of displaying information on a screen to excite the eye to a respose. I will just look at two types The LCD and the LED screen.

The LCD screen uses a matrix of three filters arranged as three "stripes" of colour filters arranged in a square. This forms one pixel. Put a magnifying glass to the screen and you will see this formation. These filters allow a measured amount of light of each of the primary colours to pass through according to the digitised amount of each colour, illuminated from behind by a white electro lumescent screen. I am not sure of this I think LCD uses CMY as the colours because they filter and LED wil use RGB because they emit but it could be the other way around.

The LED screen emits light in the three colours in the same way but each LED is its own source of light of which the intensity is controlled by the digitised control signal as before.

The eye of course perceives these tri colour spots as a single colour which has as many different tones as the bits of the digitised signal allow.

When you are observing a spectum of a star for instance the actual colour of the various sections will depend mainly on how your screen is set up. The aim here is not the actual perceived colour but the position and number of dark lines that appear on the spectrum corresponding to the absorption spectra of the elements in that star that define its construction and its relative speed.

Barry

[robz]

Getting back on track.....................is a CD or DVD usable or just rubbish as a star spectroscope?

Before I start building proper holders etc.,I need to know if I'm wasting my time.

Should I be using a glass prism instead?:help:

[Merlin66]

Barry,
thanks for that...It's sometimes amazing the things we take for granted..
Looking at my laptop screen with a x30 loupe certainly shows the blue/ green/ red elements.
For the purposes of the discussion I'd still call these individual "elements" a pixel....the same as in a colour camera and the "combined" set of three a "picture box" ???
It appears under magnification, that "RED" is represented by the red pixel, some low intensity in the green pixel and zero intensity (ie black!) in the blue...so there's no de-bayering as such ie each pixel is ALWAYS RGB (In a digital image if you do the same and zoom in on the individual pixels ie Maxim/ AstroArt etc each "pixel" on the screen is one of the 64 million colours - but if you then look at each image "pixel" you see on the laptop screen it is still a collage of RGB screen "pixels")
So the size of the screen pixels will obviously define the resolution seen by the eye..
Summary:
Using a screen matrix to generate a "filter" -
A GREEN filter would be a bright green pixel and black in the other two...similarly for the others.
A non RGB "filter" would have some intensity in each pixel.....
I think the issue may be the colour of the object/ spectrum going through the "filter" if it changes quickly from one point to the other ie across a couple of "pixels" there could be colour distortion...
Certainly well worth a trial!!

[mswhin63]

Hi Robert,

Consider other options about eg: professional grade diffraction gratings and create the spectroscope shell based on dimensions. Cut the CD or DVD to the required size compared to commercial DG's and insert. If it works (great) if not you have a shell ready to insert a professional grade diffraction grating in.

Personally a CD is round and if you look carefully the data does alter the surface diffraction. this would alter the final diffraction. Being round I am not sure if the colours would reflect accordingly too, blanks may be uniform. I do not know how the the disc are created.

I too want to consider building a SS one day.

[Merlin66]

Sorry Robert....back on track....
A CD/DVD is a play thing...IMHO you can't use them for any semi-serious spectroscope work.
A 45 degree prism or better a 60 degree prism will work very well...only one bright spectrum, no zero order image, no multiple spectral orders...
Only down side is low resolution and non-linear dispersion.
(To quote " A 100 l/mm grating at a distance of 100mm will give approximately the same plate scale as a 30mm 60 degree flint prism")

[Merlin66]

malcolm,
It's almost impossible ( a word I don't use often) to cut a transmission grating without damaging it!
You can make up a mounting frame to hold the 35mm sized filters but this adds backfocus problems and complexity.
There's a design shown in the Y! group astronomical_spectroscope files area that I used with the P-H commercial 35mm gratings...

[Barrykgerdes]

I have a nice little spectroscope that was loaned to me on a long term loan some years ago. It was essentially for examining liquids. There was a minature test tube that fits in one of the holes. It has an adjustable slot, prism and viewing eyepiece all built in.

Looking at a white TV screen LCD gives colour lines in the blue, red and green areas of the spectrum. Looking at daylight from the sun gives the standard white light spectrum view showing the absorption lines, principally the sodium line. Looking at one of those energy saving floros shows why you should never use them for serious viewing of coloured objects.

Barry

[Merlin66]

A direct vision spectroscope like the one you show, can be held behind the eyepiece to show the absorption lines in Sirius and will pick out planetaries for the surrounding star field.

[AstroGuy]

Did you get a chance to check out my LCD Digital Filter thread in the ATM/DIY section?

1) Basically on a good quality LCD screen there is very little or no inter-pixel space.

2) Pixels on LCD screens used for my project do not emit light, they channel it through RGB Liquid crystal. They allow light to be filtered so that individual RGB components can be filtered and focused in the eyepiece/camera/photo diode whatever light detector exists at the focal point.

to create a spectrascopic analyser for e.g.

The LCD screen has the backlight removed so it becomes transparent, by turning on all the RGB pixels through software you can generate an entire screen of a particular colour/hue. The screen is basically mounted in front of the scope aperature and becomes a colour filter. The light that can only travel through the programmed LCD colour filter reaches the photo diode at the eyepiece end when focused. The voltage is recorded and graphed for that colour/hue. By cycling throught all the possible colours/hues of the visible spectrum and recording their respective voltages and plotting them on a graph......well you can see where this is going right? by checking particular wavelength plot amplitudes, you can see emmision and absorbtion characteristics. Keep in mind though, a 24bit LCD screen can only create 16777216 different hues/colours. So the visual spectrum can only be diced up into as many slices. Take into account though that a LCD screen mainly works at 60 frames per second. That means you can only sample 60 individual spectral lines per second!

Using this system each spectral line capable of being recorded has a bandwidth of 0.00002086162567138671875 nm (nanometres). If you wanted to do the entire spectrum you could skip every 70,000 spectral lines, this would sample the visible spectrum at 240 points from say 350nm to 700nm and it would only take 4 seconds for a preview. Because remember, you can only scan any 60 spectral points per second. Preview would not be as accurate as re-sampling the same spectral points (colour/hue) many times and taking the average, basically many short exposures that are stacked can be done through the software.

I would rather use a photo diode to gather gather the sampled spectral wavelength voltages detected at any given spectral point in the visible spectrum. I think using colour CCD's would create to much work and complicate things, not to mention costs involved. You will however have to get the data of the spectral response characteristics of the diode in question and compensate for this in software.

You would need to have the star/subject area being analysed taking up the entire eyepiece view or at least focused on the photo diode's detector/sensor for this system to work accurately.

If you were able to see the eyepiece with the star taking up the entire eyepiece exit pupil area, you would see a kind of cycling of colour from deep violet to deep red and every other hue in between. The intensities of these hues/colours is the data you would be capturing on the photo diode sensor and recording or displaying/recording as spectrographs on the computer attached to the system.

It may sound a little complicated, and a little convoluted in the way I have explained it, but if you read it a couple of times you will see the light! ;)


Anywhooooooo, I've probably bored you enough already :) I'll send you a link to those cheap components ok. You won't be sorry you checked them out.

[robz]

O.k, so it is obvious that the CD/DVD idea should be scrapped for astro work..........bummer!:sadeyes:

There are plenty of cheap 500l, 1,000l replica plastic gratings available on Ebay...................are these usesless also?

''Proper reflective diffraction gratings'' are very costly for larger sizes through Edmunds and other sources.

I guess that a 60 degree prism may be the next try............but where to get?

[Merlin66]

Robert,
If you do want to build and use a small spectroscope...bite the bullet and buy a 200 l/mm transmission grating from Paton-Hawksley - you won't regret it.
The ebay gratings are for visual effects at the disco! not for science.
You can find some 60 prisms on ebay out of India... Surplus Shed also sell a selection of prisms which are OK. I got my first one down at the St Kilda Saturday market...

[robz]

Thanks Merlin, I'll start hunting around as you suggest.:thumbsup:

Cheers,
Rob.

[AstroGuy]

Hi guys,


Does anyone know where I can get a reliable/authentic database or a list of all the known substances/periodic elements' spectra wavelength values? Preferably in a plain text data file I could import. I need it so I can incorporate it into the LCD Digital Filter project so it can also function as a Digital Spectroscopic Analyser.

If anyone could point me in the right direction, I would really appreciate it.

cheers!

[Merlin66]

http://physics.nist.gov/PhysRefData/Handbook/Tables/hydrogentable2.htm

The NIST site is a wealth of knowledge for all the elements and their associated spectra - I've selected Hydrogen as an example.

[AstroGuy]

Thanks for that. Some very useful data. At least I can incorporate the basic periodic elements data into my project to start with. It would be nice to have all the organic compounds/all the known chemical molecules and isotopes etc...Unfortunately everywhere it's available wants you to pay a fair wack for it. Hard when you are trying to keep it free.

Thanks again...

[robz]

Have just come accross this :

$64.00 : 3 prism spectroscope, non adjustable slit (very small)

any thoughts?

[mswhin63]

I was looking at exactly the same thing a few weeks ago and I was going to purchase one because they are quite cheap if it doesn't have a slit in that I was thinking about creating one. still waiting, shoulder to get better before I start outlaying money.

it primarily works with a prism, I believe the best method would be using diffraction grating is parts the prism could be a good starting point.

[Merlin66]

These Direct Vision spectroscopes are fun and can be used visually (held behind an eyepiece) to show the spectra of the brighter stars.
They can be trashed to extract the Amici prism (and sometimes the slit) which can then be used to build a small astronomical spectroscope.
The prism gives a non linear dispersion which makes calibration a PITA.
I'd still save your money for a decent grating.

[robz]

Roger that Merlin.
Will be purchasing a P.H grating in the near future.:)

[Merlin66]

http://cgi.ebay.co.uk/PRISM-GLASS-EQUILATERAL-50mm-EDGES-/120697983419?pt=UK_Collectables_Sci entific_MJ&hash=item1c1a2911bb

You could go back to basics with this one...

[robz]

Thanks Merlin.
Definitely cheap enough, but would it be of sufficient optical quality towards a usable star spectroscope?

It's ''non worked glass'' so I don't know how that will affect resolution?

Would it be similar to a 1200l/mm DVD grating?

The DVD grating in a test set up recently showed many clearly defined Fraunhofer lines on solar light and surprised me a bit as I didn't expect much from it at all.

[Merlin66]

You're caught between getting good results with a lesser quality prism or paying the "extra" to get a quality grating. A bit like using cheaper eyepieces...they will do the job but not as well as a TV etc.
Hartung used a 60 degree prism to help identify planetary nebulae in his book. A small prism unfortunately would not be as good as a small grating....keep saving your money for that SA100.

[robz]

Yes, that is the dilemna at the moment:shrug:

I will make a spectroscope of some sort this year. What form/ shape or materials used is yet to be determined.:rolleyes:

I'm looking very closely at the LHIRES2 in Buil's literature and will be making something along those lines...........only ''simpler'' and as compact and cost effective as possible.

No doubt there are many future spectroscope builders out there who are wanting something simple but also cheap...............tall order?...........maybe.
Wish me luck:D