Question: Can I use a DVD or does it have to be a DVD-R ?

tmanmerlin is asking a question about spectrometry: Subscribe to answer questions on this topic

tmanmerlin asked on June 09, 2018 22:56
87 | 3 answers | shortlink


I looked around and could not find a specific mention of this point. thanks.



dvd

question:spectrometry question:dssk



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3 Answers

Hi @tmanmerlin and welcome to the publiclab.

Find instructions to build the difraction grating here: https://publiclab.org/notes/MrBumper/01-11-2015/preparing-a-dvd-r-to-act-as-a-diffraction-grating


tmanmerlin 4 days ago

Hi, thanks. I read through this article, it implies that any DVD could be used, assuming it is splitable. But it doesn't specifically state if there is some property of DVD-R that a DVD (non -R) doesn't have.

My question is better phrased, is there some property that a DVD doesn't have that makes it unsuitable.

I split two DVD's I had, and they separated awesomely, the aluminum was on the top, the bottom was relatively clean of aluminum.

However, the bottom was not purple, like the one I got in my kit. So that is why I started looking at using some old DVD's I had.

I'm gonna have to go get some DVD-R if that is a specific requirement.

I see below that someone said a CD could be used, and it might have better line width. So I have a lot of old CDs. As long as they are splitable, do you all know if they would then be usable, assuming the aluminum sperates as needed.

Thanks in advance, looking forward to this project.

tmanmerlin 4 days ago

Tried to edit my answer. I meant that since my split DVD bottoms didn't have purple, I was concerned they were not usable.

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No a DVD is not suitable. The majority of pressed DVDs are single layer, so they cannot be split to expose the (grooves/pits and lands) diffraction and aluminium layers.


tmanmerlin 4 days ago

i got lucky on two ol DVD's, they split much easier than the DVD-R I got. I'm just concerned they would not be usable because of some other property, as I mentioned in my long reply above. Thanks for the answer.

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True, the physical layer aspect is one issue. The other fundamental issue is the 'line spacing' of the recording 'tracks' which form the diffraction grating -- which produces the spectrum. The 'wider' tracks of a CD are a better match to the webcam optics.


tmanmerlin 4 days ago

Just to be clear, If I can effectively split a CD, and get a clear bottom, it is totally usable. I see you are saying that, clearly, but want to be extra careful. Thanks for the answer.

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