solar spectrum seen in DVD

[nytecam]

In case you haven't tried it here's a couple of pics from this afternoon with my 300D cam focused on infinity brought very close to DVD surface with sunlight skimming its surface. Works even better viewed by eye with maybe hundreds of Fraunhofer absorption lines visible across a colourful spectrum - good luck

[Gina]

Yep - diffraction spectrum

[nytecam]

Yep - diffraction spectrum

Well done Gina - a team point !

It's over a decade [before DVDs had arrived] that I had a play with CDs to produce a solar spectrum @ http://home.freeuk.c...in/solaspec.htm but at our Society's Users Group recently it was suggest that it didn't work with some DVD but no explanation given - hence my recent experiment were it worked fine on a virgin DVD. Of course the CD or DVD is a poor substitute for a real diffraction grating [which are expensive] but can whet the appetite of the enquiring mind My CD spectrum vid here...

[yesyes]

Interesting. I take it that this couldn't be used on stars, except maybe for a handful of very bright ones? Maybe a DVD fragment could be mounted at the best angle in a 1.25" or 2" barrel for some low cost spectroscopy?

Incidentally, the other day I used the same method to demonstrate to someone that energy saving light bulbs do not emit light across the full visible spectrum (as incandescent bulbs do), but only have some rather narrow lines at red, orange, green and blue.

[nytecam]

Interesting. I take it that this couldn't be used on stars, except maybe for a handful of very bright ones? Maybe a DVD fragment could be mounted at the best angle in a 1.25" or 2" barrel for some low cost spectroscopy?

Umm - interesting - worth an experiment [staranalyser transmission grating ~£90] with a clear DVD/CD off-cut [ali coat stripped with sticky tape??] immediately before the eyepiece or better before a camera at prime focus - give it a go

Incidentally, the other day I used the same method to demonstrate to someone that energy saving light [ESL] bulbs do not emit light across the full visible spectrum (as incandescent bulbs do), but only have some rather narrow lines at red, orange, green and blue.

Yes - that's a great demo of ESL - how easily the eye is tricked into believing it's white light

[yesyes]

Umm - interesting - worth an experiment [the 'normal' Staranalyser transmission grating ~£90] with a clear DVD/CD [ali coat stripped with sticky tape??] immediately before the eyepiece or better before a camera at prime focus - give it a go

I was thinking maybe a diagonal would be easier. Take out the mirror and install a DVD fragment at a good angle...

[nytecam]

I was thinking maybe a diagonal would be easier. Take out the mirror and install a DVD fragment at a good angle...

You can give it a go but I've assumed it wouldn't work. Light onto the grating should be collimate eg parallel to get a sharp spectrum. It works with a transmission grating placed at right-angles to a convergent beam as the depth of the defracting surface is negligible. Off an inclined surface [like a 'flat' as suggested] it's not the case so whilst the colourful spectrum is there any line structure is blurred.

But anyway it cost nothing to test it - good luck

[yesyes]

Oh yes, what you say makes a lot of sense, now that you said it.. ;-)

Removing the reflective coating on a DVD isn't too hard, so I might try your way...

[Gina]

Yes, they de-laminate quite easily

[nytecam]

Here's a close-up where solar blue spectrum 1st order

overlaps the 2nd order spectrum

and difficult to know which line belongs to which part of the spectrum eg blue end or red end. It's usually sorted/separated by using a red or blue filter in the light path.

The 2nd order spectrum [red here] has twice the dispersion/resolution of the 1st order

[Auntystatic]

There are a few interesting posts on this subject in the spectroscopy part of the forum