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Author Topic: Can a digital camera be used as a spectrometer?  (Read 39697 times)

Offline Damo the Optics Monkey

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Can a digital camera be used as a spectrometer?
« on: 25/02/2009 11:31:49 »
This is one of my many ongoing projects (asides from teaching, a few inventions, a Masters and being beat up by 7 year olds).

I have a Canon G10 - a pretty sweet camera with incredible features, detailed here.

Does anyone know of any other attempts to use a camera as a spectrometer?
« Last Edit: 27/02/2009 08:21:30 by chris »


 

Offline girts

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Re: Can a digital camera be used as a spectrometer?
« Reply #1 on: 25/02/2009 15:56:10 »
I doubt one can get a valuable information out of a digital camera. It probably changes the reading of sensors to fit the human expectations of a picture - makes it more nice to a human eye. I have however no facts behind my biased opinion.
 

Offline RD

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Re: Can a digital camera be used as a spectrometer?
« Reply #2 on: 25/02/2009 16:09:54 »
Fitting a transmission type diffraction grating to a camera will split light into spectra.

Cokin make a filter which can be used for this purpose ... http://www.astrosurf.com/buil/us/spe1/spectro3.htm

Or a cheaper option would be these diffraction spectacles ... http://www.mutr.co.uk/product_info.php?products_id=1009604
« Last Edit: 25/02/2009 16:13:41 by RD »
 

Offline Damo the Optics Monkey

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Re: Can a digital camera be used as a spectrometer?
« Reply #3 on: 26/02/2009 08:39:24 »
they are pretty darn cool!  Thank you for the links I will have a closer look at them.

Thankfully the g10 has RAW format as an option
 

Offline RD

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Re: Can a digital camera be used as a spectrometer?
« Reply #4 on: 26/02/2009 16:49:19 »
Another source of cheap diffraction gratings ...


Quote
DIFFRACTION GRATING (Experiment Pack)

This pack contains 3 different transparent film holographic transmission diffraction gratings. 1000 lines/mm, 500 lines/mm and a crossed axis grating . The high line density produces a wide coloured spectrum of the observed or projected light source similar to a prism. Make a hand spectroscope. Size 15.2 x 3.8cm sufficient for four 35mm slideholders which can easily be made from the cardboard box. Instructions and experiment sheet included.   
 Ref: OPF0002 | Price: £7.99 |
http://www.greenweld.co.uk/acatalog/Shop_Experimental_75.html
« Last Edit: 26/02/2009 16:52:24 by RD »
 

Offline Bored chemist

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Re: Can a digital camera be used as a spectrometer?
« Reply #5 on: 26/02/2009 18:27:30 »
The really cheap option is to use a cd as a diffraction grating.
 

lyner

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Re: Can a digital camera be used as a spectrometer?
« Reply #6 on: 26/02/2009 22:12:01 »
You would need to burn your own CDROM with the appropriate data or you wouldn't get the purity of spectrum from it. The grating must be really uniform even if its dimensions are not known (you could calibrate it).
A pretty looking spectrum from a shiny CD doesn't mean it would be any use as a measuring instrument of any worth. I'm not even sure that you could produce uniform grooves over a wide enough area for it to work.
 

Offline RD

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Re: Can a digital camera be used as a spectrometer?
« Reply #7 on: 27/02/2009 03:13:35 »
Quote
The performance of this ultra-low cost spectroscope is comparable with instruments typically costing £80. It uses a CD or DVD as a reflective diffraction grating and clearly shows Fraunhofer lines in the spectrum arising from natural light – and distinctive emission bands from artificial sources such as sodium lamps. Differences between fluorescent lighting tubes – e.g., white light or ‘warm’ light types - can be easily identified by their distinctive emission bands.



 
The spectroscope is made from virtually indestructible polypropylene and supplied in flat pack form – taking about 30 seconds to assemble. It comes with a free CD but can be used with any CD (or a DVD for higher resolution).

Nb. The really intriguing aspect of this device is the use of a common place CD or DVD replacing either an expensive prism or specially made diffraction grating.
http://www.mutr.co.uk/product_info.php?products_id=1009497
« Last Edit: 27/02/2009 03:32:42 by RD »
 

Offline Bored chemist

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Re: Can a digital camera be used as a spectrometer?
« Reply #8 on: 27/02/2009 06:59:12 »
For the old fashioned amomng you, you can also use a vinyl record as a grating. LPs work better than singles.
 

lyner

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Can a digital camera be used as a spectrometer?
« Reply #9 on: 05/03/2009 11:31:51 »
Excellent for a spectroscope (qualitative) but not for a spectrometer (quantitative).
 

Offline Bored chemist

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Can a digital camera be used as a spectrometer?
« Reply #10 on: 05/03/2009 19:28:44 »
The picture RD has kindly provided gives a set of lines. My guess is thery are the mercury lines (mainly) and I can look up the wavelengths of those.
I could, in principle, get a similar picture of the spectrum of light from some other source and, by comparing it to the mercury spectrum, I could find out what wavelengths were present.

That looks like a spectrometer to me- albeit not a vrey good one.

What would be more of a challenge would be to measure the intensity of the light at each wavelength but, in theory, the digital camera records the intensity at each pixel at each of 3 wavelength bands (or at least soemthing like that).
You could add those together across pixels and along the spectral lines to get a measurement of the intensity of the line.
Then you could do much the same thing with, for example, a tungsten lamp at a known temperature- which gives a known relative amount of light at each wavelength.
From that data you could constuct a calibration of sensitivity versus wavelength.

It would be a total pain in the neck, but you could make a spectroscope, a spectrometer and a spectrophotometer out of that rig.
 

lyner

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Can a digital camera be used as a spectrometer?
« Reply #11 on: 05/03/2009 23:06:41 »
I think you'd be trying to make a silk purse out of a sow's earhole, actually; albeit a pretty one. I doubt you could resolve Zeeman splitting, for example - or red shift for a distant star.
Horses for courses, surely.
 

Offline Waquinn

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Can a digital camera be used as a spectrometer?
« Reply #12 on: 02/05/2009 23:26:54 »
This is my first time on any Forum, apologies in advance.
I do not agree that a home made spectroscope based on a CD/DVD is totally useless.
I have constructed a home made spectrometer using a CD/DVD as a reflection grating.
It is based on a rotating table which has a rectangular piece of CD/DVD attached..
The rotation of the table can be used to read the wavelength, but I use a 2MP webcam to take a video of the spectrum. This is then stacked using RegiStax (to improve S/N), edited and cropped, and finally desaturated using GIMP. I use vspec to convert this image into a profile of intensity. It can easily resolve lines at 542.2nm and 546.5nm. Intensity, of course, can only be compared if the device is calibrated.
 

Offline Bored chemist

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Can a digital camera be used as a spectrometer?
« Reply #13 on: 03/05/2009 15:48:36 »
Sounds like an interesting project. Now all I need is a strong enough magnetic field to split a line by about 4.3nm and I can use your machine to resolve Zeeman slitting, thereby refuting sophiecentaur's conclusion.


(I know that, in practice, a better spectrometer would be easier than a strong enough magnet)
 

lyner

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Can a digital camera be used as a spectrometer?
« Reply #14 on: 03/05/2009 23:47:35 »
This rotating table sounds more like a piece of lab equipment than a 'kitchen table'.
Seriously, it sounds like the makings of a workable system and a few years ago a digital sensor array would have been a well sexy bit of lab kit.
But I'm not sure where this is taking us. A CD is a handy form of grating but hardly worth considering if you want good results.
 

lyner

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Can a digital camera be used as a spectrometer?
« Reply #15 on: 05/05/2009 11:29:01 »
Also, Waquinn, why not use a uniform grating? Any non uniformity in the spacing (due to even basic formatting info) will affect the dispersion and the purity of the diffraction pattern.
Pretty, as I said before, and very informative but a 'scope' not really a 'meter'. Are gratings really that expensive? I seem to remember we had a boxfull when I was at Uni - decades ago.
 

Offline Bored chemist

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Can a digital camera be used as a spectrometer?
« Reply #16 on: 05/05/2009 20:28:39 »
I don't supose you had boxfulls of CDs when you were a student but do you understand just how cheap a CD is?
The encoding on CDs is carefully designed to avoid having too much patterning in the pits and troughs so it tends to look like noise in the spectrum. They clearly are not ideal but there's no question that you can use a CD as a good enough grating to resolve the two lines that Waquinn talks of.
Also, I still stand by my assertion that, given a calibration like the mercury spectrum (or, at a pinch, a copy of the red book) you could measure the wavelength of the light.

Nobody is saying that this would be much better than a toy, but for toys cheap is good.
BTW, I meant this red book.
http://en.wikipedia.org/wiki/Red_Book_(audio_CD_standard)
 

lyner

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Can a digital camera be used as a spectrometer?
« Reply #17 on: 05/05/2009 22:31:55 »
(A) boxfull of 45s, actually.

Blank CDs are as cheap as chips, I know. The rest of the device wouldn't be free, though, and the incremental cost of a grating seems so low that the benefit would seem to make it worth while.

I don't quite know what you are getting at about the coding of the data on the disc. There is extensive interleaving and redundancy to reduce the effect of isolated, large, faults to produce noise rather than splats. But there is nothing as simple as a regular set of stripes, which is what a  diffraction grating really requires.
 

Offline Bored chemist

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Can a digital camera be used as a spectrometer?
« Reply #18 on: 06/05/2009 20:33:09 »
Imagine that I cut a bit from a CD to use as a grating. If the data on it were such that half of it was covered by 1,1,1,1,0,0,0,0,1,1,1,1 etc but the other half had 1,1,0,0,1,1,0,0... then the 2 parts would give seriously different diffraction paters. That would mess up my sppectrum badly.
But the encoding is such that regular large sequences are forbidden so all I see is the basic "pitch" of the tracks and some effectively random noise from the data.

Incidentally, if you look at this
http://www.exo.net/~pauld/activities/CDspectrometer/cdspectrometer.html
Or this
http://www.mutr.co.uk/product_info.php?products_id=1009497

you will see that by far the most expensive part of the putative spectrometer (and I accept that they have built a 'scope rather than a 'meter) would be the camera and the software. But many people have already got that; they also have lots of CDs.
Not many of them have a purpose made diffraction grating (and the cheap ones are pretty cappy anyway).
As I said, if you want a spectroscope as an educational toy the CD is probably the best bet for a cheap grating.
« Last Edit: 06/05/2009 20:38:55 by Bored chemist »
 

lyner

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Can a digital camera be used as a spectrometer?
« Reply #19 on: 07/05/2009 00:35:27 »
The fact that the pattern of holes on a CD is random makes things worse! What you need for a good diffraction pattern is a uniform set of stripes and not a set of parallel rows of random tiny holes.  The modulation will produce a serious broadening of any spectral lines, negating the point of having a lot of stripes. You don't need a particularly fine grating, in any case - you can do the sums as well as I can.
I have a feeling that, if you wanted a good, cheap, substitute for a diffraction grating, you might be better off with a bit of holographic wrapping paper or a Christmas decoration- if you chose the right pattern. They have relatively simple patterns on them with large areas of the same spatial period, which is what you want. Just cut out one bit which is all the same and it could give you and excellent result.
BTW, Rapid Electronics will supply a 50X50 mm grating with 300 lines per mm for £9.00. Why not do the job properly?
 

Offline Bored chemist

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Can a digital camera be used as a spectrometer?
« Reply #20 on: 07/05/2009 08:07:15 »
"BTW, Rapid Electronics will supply a 50X50 mm grating with 300 lines per mm for £9.00. Why not do the job properly? "
To save about £6

 

lyner

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Can a digital camera be used as a spectrometer?
« Reply #21 on: 08/05/2009 00:23:53 »
Telescope, camera, table, etc + CD  vs Telescope, camera, table, etc + £9

What is the difference in cost as a percentage and what is the difference in performance?  The £6 would be well spent, in my opinion. Most Scientists are after the best possible result for as much money as they can afford.
 

Offline Waquinn

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Can a digital camera be used as a spectrometer?
« Reply #22 on: 08/05/2009 23:02:16 »
My spectroscope if definitely homemade. The tracks of a CD/DVD form the reflection grating; the track pitch of a DVD is 0.74um. This is a lot better than 300 lines per mm.
Unfortunately, first results using a DVD instead of a CD were not as good as expected.

Operator error I'm afraid. I did not change the settings from the CD.
I am also having difficulty calibrating the amplitude response using a known amplitude profile source (a light bulb) especially in the near infrared.
I agree with other contributors, there is no replacement for the correct tool. However, it does exactly what I need it to do for now to test my prototype. Buying a spectrometer without testing the basic parameters of my design would have been a waste.
 

Offline Bored chemist

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Can a digital camera be used as a spectrometer?
« Reply #23 on: 09/05/2009 19:45:58 »
Telescope, camera, table, etc + CD  vs Telescope, camera, table, etc + £9

What is the difference in cost as a percentage and what is the difference in performance?  The £6 would be well spent, in my opinion. Most Scientists are after the best possible result for as much money as they can afford.
Guess what? The person who originally wrote to ask if one can use a camera as a spectrometer already has a camaera.
Unless you want to look at the spectormeter from a long way away I don't see the point of the telescope and I doubt that you will find many households where they don't have a table, and you could use the floor anyway. So what we are looking to compare is the £9 for a diffraction grating and the £2.90 +vat for the spectroscope kit that they sell at MUTR.
In percentage terms that's about 300%.
It's true that most scientists are after the best kit they can afford but I am not sure this is really about scientific equipment, but more along the lines of an educational toy. I still think that a CD will do a pretty good job for no cost.
In any event, Since Waquinn has kindy provided us with a spectrum taken using a CD I don't see how anyone can deny that it's possible.
« Last Edit: 09/05/2009 19:48:20 by Bored chemist »
 

lyner

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Can a digital camera be used as a spectrometer?
« Reply #24 on: 10/05/2009 10:51:56 »
BC, if you want to see spectral lines you need some optics to produce a good beam of light from a slit. That is what I meant by "telescope". What other source could be used? The 'slit' also needs to be narrow and bright enough to see and resolve the lines and some optics (albeit simple) will improve matters. Is the proposed / described arrangement just a slot with bright sunlight shining through it?
I never suggested that it couldn't be done with a cheap and cheerful CD but, if you don't do your best, you end up with a qualitative not quantitative result.
 

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Can a digital camera be used as a spectrometer?
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