Solar Spectra @ 1.8A/pixel

Merlin66 (Ken) · #1 14-12-2007, 03:25 AM

Nothing too exciting, using the 135mm FL spectro with a 600 line per millimetre grating, 40 micron slit and the Canon 350 (un-modified). The resolution is about 1.8A/ pixel.
Shows a couple of things: Within two frames you can record all the spectrum from UV through to the far Red ;see how the responce of the 350 drops off in the red! and it also shows the slit was not square to the grating and the width ( 40micron) too large!
The graph has been corrected for the camera responce ( Vspec) and a few noticable lines marked.
Other than the slit ( now fixed!) the spectroscope works very well.
My headache from the beginning has been guiding..... I'm now on the MkIII beamsplitter design and still not there. Using a Rainbow/ Baader/Star Analyser transmission grating is 200% easier but the resolution suffers.
Anyway, thought I'd share........

iceman (Mike) · #2 14-12-2007, 06:20 AM

Very cool! I think that's the first spectrum image on IIS! Thanks for sharing!

[1ponders] (Paul) · #3 14-12-2007, 09:46 AM

Science in action on IIS

rogerg (Roger) · #4 14-12-2007, 10:39 AM

That's great, you must have gone through a lot of work to get to this point! I once went down the line of spectroscopy. Bought a book and tried to understand how I could do it. I started trying to make my own spectrascope (not wanting to fork out the $$$$ for a real one), from a Cokin rainbow filter and so on. Didn't get far, eventually gave up. It was a huge steep learning curve which I just couldn't climb. Chose a different steep learning curve instead

I have high respect for amateurs who do manage to achieve accurate spectra results

Merlin66 (Ken) · #5 14-12-2007, 06:57 PM

If I were starting again, I would definately start with a Rainbow/ Star Analyser/Baader type transmission grating!
These look like a bit like a regular 1 1/4" filter and just screw into the eyepiece ( for visual work) or into the nosepiece of a CCD adaptor. With this simple set up you can obtain some wonderful star spectra. By adding a slit infront of the eyepiece it can be "modified" for use on the Sun or expanded objects ie planetary nebulae, comets etc etc.
A wonderful introduction at the same cost as a good eyepiece.
In the meantime I continue to search for the Holy Grail......

bojan · #6 14-12-2007, 09:47 PM

Very interesting and simple diffraction spectroscope can be made of old CD or DVD blanks, as described on the links below:
http://astro.u-strasbg.fr/~koppen/spectro/spectroe.html
http://littleshop.physics.colostate....ctroscope.html
http://sci-toys.com/scitoys/scitoys/...ctroscope.html

Merlin66 (Ken) · #7 14-12-2007, 10:12 PM

A good way of experimenting. Has some limitations for imaging. Tonkin's book has a whole chapter on CD/DVD set up's.

Robin Leadbeater has a good write up on the StarAnalyser
http://astrosurf.com/aude/spectro/ohp2007/index_en.html

Merlin66 (Ken) · #8 15-12-2007, 03:46 AM

As mentioned my nemisis is getting the spectro to guide on the star with sufficient accuracy on a 20micron slit. Well, I think using a 70/30 beamsplitter in an OAG body has got me there!!!! ( check back when I can get some clear skies to put it through its paces) At least I can repeatably position the artificial star in/on the slit and have a good image for guiding..... let's see what happens in real life!

Another option is to use a cylinderical lens to form an extended linear image of the star, then present that to the grating.
Fulvio Mete www.lightfrominfinity.org/ has been doing some excellent work with such a concept, applied to a standard spectro. My idea it to apply it to a transmission grating to give "better" resolution. Finding a suitable FL and position is a challenge..... the benefits are that you don't have to guide on the slit- the star image makes its own one!

Straylight · #9 15-12-2007, 12:32 PM

I grew up in the same street as the guy who invented the atomic absorption spectroscope, Alan Walsh. He was made a knight. Never really knew him though.

Useless piece of information no. 415982763

Heian (Mark) · #10 17-12-2007, 10:11 AM

Nice spectra Ken,
I've been slowly working on getting a "reflective slit" (needle) solar instrument together based on Maurice Gavin's design. The best resolution I've got to date has been a 2.5 A/px by putting the star analyser in front of a 135mm slr + 2x teleconverter on the 350D. Makes interesting spectra of street lights!

On a rare clear night recently, got a good spectra of Fomalhaut..

For the "needle" instrument, I've got some transmission grating, 500 lines/mm, so it'll be interesting to see how well that works.

Merlin66 (Ken) · #11 17-12-2007, 07:21 PM

Sounds like a great project!
270mm FL is a fair dispersion for a SA grating, so you'll need a couple of frames to fit it in and a longer exposure, guessing 3 -4 sec.
You may want to make a set up like Samir has on his webpage (www.samirkharusi.net/spectrograph.html) to at least get the arrangement working. I use a cardboard box 1200mm long to get focus with my Zuiko 135mm telelens. A Dulux fluro energy saving lamp has some good reference lines for calibration. Could be easily adapted to use the needle slit.
Keep up the good work!