The spectrum you show doesn't look correct....sorry.
What set-up are you using, can you explain the spectrograph design you're using?
Over on the astronomical spectroscopy group, in the files area there's a copy of the design spreadsheet - SimSpec which can be used to define and analyse your design. https://groups.yahoo.com/neo/groups/...troscopy/files
That is better but I see the white corner is blocking some more features and the focus could be tweaked up.
Is there any way to move the spectrum to the middle of the sensor?
I must say the plot reminds of a sodium lamp or CFL spectrum but reversed, i.e the red end at the left. The spectra should be produced with the blue to the left side.
BASS is the best of those packages, simple to use and produces nice looking charts.
As a newbie to spectroscopy myself, I can appreciate the frustration in getting started, and the excitement when you start to see some results. Don't be too disheartened - you are starting to capture some clear emission lines, so rapid progress should be possible from here!
As others have said, it would help if you can describe the equipment you are using (OTA / lens, grating / prism, camera / sensor, etc), so we can help point you in the right direction. Is this a home-built device, or are you using proprietary components?
Looking at your spectrum image, is that the whole frame, or is it a crop? Can you do anything within your sensor assembly to eliminate the white corners? (It looks like some sort of light leakage or internal reflections.)
The spectral analysis software will interpret any non-black pixel within the sampling region as "signal", so you want to shift the spectrum well clear of the white "vignetting" in the corners, and also maybe reduce the overall exposure so as to darken the general background.
Also, try to make sure you get the whole spectrum within the frame, and if you are using a transmission grating (like a Star Analyser), try to capture the "zero-order" image of the light source on the frame, as well as the first-order spectrum.
For your first attempts, try shooting a known type of emission light, such as a fluorescent tube, compact fluorescent globe, or sodium street light as your light source (it looks like you have used one of these), and then you can use the known (or suspected) emission lines of the light source to calibrate your spectroscope. Fluorescent lights typically show several strong Mercury lines at 434.7 & 435.8 nanometres (blue - but you'll only make this out as a single line, if at all), 546.1 nanometres (green), and 614.9 nanometres (orange-red). You'll see some other lines as well, due to the phosphorescent coating and other elements, but these are the dominant lines that you can use to calibrate from a fluorescent tube source. Sodium lights produce strong yellow lines at 588.9950 and 589.5924 nanometres (but again, you'll only see this as a single line).
Once it is calibrated, you can start capturing other spectra from other sources, and use the same calibration to interpret the spectra that you capture. (The modern "Brilliant White" LEDs are interesting, as they have a strong narrow blue band from the single blue LED "driver", and a broader band across green / yellow / red re-emitted by the phosphors. The older "White" LEDs which have three RGB LED "drivers" produce a completely different spectrum, showing three strong but overlapping bands from each of the red, green and blue LED "drivers".)
To indicate what can be captured easily indoors while getting to grips with your equipment - the attached spectra were captured last night using a Star Analyser 100 grating and a QHY5 mono astro-camera. I used a 10 mm ball bearing to reflect the light source as a tiny pin-point of light against a matte black background, with my telescope and camera set up at the other end of the darkened room (about 9 metres away)
Fluorescent Tube: Note the intense mercury emission lines, and the "zero order" spike of the un-diffracted light source, used to calibrate my camera / grating set-up
Ditto (with Mercury Lines superimposed)
Halogen Globe: Note the typical "black body" continuous spectrum from an incandescent light
RGB "White" LED: Note the three overlapping peaks, corresponding to the Red, Green and Blue LED light sources in these older "white" LEDs
Brilliant White LED: This newer type uses a single intense Blue LED as the "driver", and a broad-spectrum phosphor which absorbs a lot of the Blue, and re-emits as a broad Green / Yellow / Red to produce a brilliant "white" light
Hi Guys. thanks very much for all the info, to get spectrum I just put light gide on white bit as shone in attachment(2).jpg, no idea what gratin is, image is cropped, I used a standard NEON as in TEST 27 .JPG, yes it is letting light need to sort that out.
You have the neon calibrated so you can work out the dispersion of the set up and note it. Then go back to your original spectrum and do a one point calibration, entering the dispersion from the neon one. That will show you what emission lines you have.
You'll need to sort out the light ingress though, and your image is very "blocky" which might lead to some resolution issues. What sort of camera are you using Peter?
Hi Stu, As you say I will sort light ingress, sorry but I am afrad I don't know any thing about how to setup spectroscope what is [ dispersion of the set up?] is there any where I can get the info, the NEON I have in is not very barite it is out of a screwdriver have a beter one coming.
I assume you have come by this spectroscope without any real information on its design, rather than building it yourself, and you don't have a copy of the technical specifications? If you have the make and model, you can probably find a technical manual / specification on-line somewhere.
You probably need to consult a basic spectroscopy reference book to understand the working of your device. There is a wealth of information available - Ken M Harrison (aka merlin66 in the IIS forums) has written several excellent and affordable books for amateur spectroscopy, and the links that bojan provided in his first response will also provide great information.
In principle, your instrument takes a beam of incoming light, and reflects it off a grating with numerous very closely spaced lines, such that it spreads into a spectrum. The "dispersion" is the angular width of the spectrum - the finer the lines on your grating, the greater the dispersion (i.e. the wider wider the angle), and the finer the detail you can resolve, but you may only be able to examine a part of the spectrum at any time, if the whole spectrum is wider than your camera sensor. (My Star Analyser 100 grating allows the whole spectrum to be captured in a single frame, but cannot show as much detail as your type of instrument.)
Hi Stu, As you say I will sort light ingress, sorry but I am afrad I don't know any thing about how to setup spectroscope what is [ dispersion of the set up?] is there any where I can get the info, the NEON I have in is not very barite it is out of a screwdriver have a beter one coming.
peter
I have attached a picture to help you Peter. A quick neon lamp spectrum calibrated on 2 lines for clarity. You will see the dispersion of the set up I used (yours will differ) at the bottom of the BASS screen (see attached picture).
Once you have written that number down, you can go to your original spectrum and do a "one point" calibration (this assumes you know what one of the lines is, or likely to be). Click "finish one point calibration" and BASS will ask you to enter the dispersion factor from your neon. Et voila, hopefully you will have a good calibration. Try something obvious first, like a HPS street light and see if youre getting ball park dispersions (then you know if your guesswork with the lines is correct or needs adjustment)
Hope this is helping and not confusing you more! Again, like Julian, i'd recommend Ken Harrison (Merlin66) books on spectroscopy.
Last edited by StuTodd; 26-08-2016 at 02:41 PM.
Reason: clarification of point
Hi Stu, That is really good and not confusing at all, you have put it so it makes sense in English not as most are in computer speck, I really appreciate all your help, getting old dos not help, will do as you say.
Peter,
you seem to have jumped in head first....
The instrument seems to be a "modified monochromator"
OK
As mentioned, if you can obtain a usable spectrum of a known source - a fluoro lamp is one of the easiest, then you can use the known emission lines to calibrate. This will then give you the dispersion (Angstrom/ pixel or A/mm) and also the R value which defines the resolution.
BASS is a good and easy spectral processing software - recommended.
I'm sure things will become a little more obvious when you get some practise.
Onwards and Upwards.
Hi Ken, Yes it is in head first, had to go this way pension will not rune to get a commercial one, I will do as you suggest, which is the best of your books for me I need one that is PHD not all technical of innards of spectroscope, thanks for your advice.
Peter,
There are two aspects to the spectroscopic "learning curve"....
The first is to gain an understanding of what a spectroscope does and why...
This unfortunately requires some basic maths and a bit of reading.
Things like diffraction, dispersion, resolution and what a spectrum looks like for different optical arrangements. The next stage is to consider how to calibrate a spectrum in wavelength and present the result in a format which is usable.
The other aspect is to understand the elements/ components of the spectroscope and how they interact with each other...
The entrance slit, the collimator, the imaging lens and the camera all have a role to play in obtaining a usable spectrum. Lastly comes the interface with the telescope and how to actually obtain a spectrum of an astronomical object. The exposure required can extend over many minutes, hence a solid rigid arrangement which can track/ guide on the stars is important.
I would recommend "Astronomical Spectroscopy for Amateurs" as worthwhile reading, it covers all of the above.
Also check out the various pages on Christian Buil's website. He has a wealth of knowledge and experience to share.
Hope this helps.
I would highly recommend "Astronomical Spectroscopy for Amateurs" - it covers all of the key material, and you don't need to have a PhD in Astrophysics to understand it all! It's available as an eBook download from all the usual sources, so you can start reading tonight.
If budget is an issue (and let's face it - it always is!), you might want to look at acquiring a Star Analyser 100 filter. You can buy one for about $200, and it will work with a webcam or DSLR. While it can't produce the resolution of more sophisticated instruments, it will give you the ability to capture some useful spectral images of the brighter stars the very first night that you fit it to your telescope or camera, even if you don't have a tracking mount.
Hi Ken and Julian, Have ordered Astronomical Spectroscopy for Amateurs, Ken Telescope and guiding is no problem I guide on stares and deep sky for a quite a long time 300 seconds and longer, the 2 CCD I have are a Starlight Xpress Loadstar and a H9C.
