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
190 | 5 answers | #16461


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



0 Comments

Log in to comment

5 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


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.


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


Log in to comment

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.


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.


Log in to comment

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.


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.


I'm really puzzled as to where you are getting CDs and DVDs you can split. As far as I know all commercial pressed CDs are single layer and so are DVDs. The clear polycarbonate is moulded into a disk with the pits and lands that represent the information. It is vacuum flashed with a reflective aluminium layer and then spin coated with a clear lacquer. One single disk of moulded plastic with two coatings - nothing to split. And my article on preparing the diffraction grating specifically says DVD-R in the title and throughout. I just don't see the ambiguity.


I split a software DVD and was able to get spectra from it. I asked because I had a question, and the question was, if a regular DVD would produce a spectra.

The picture I will post below as an answer indicates that, at least for the regular DVD I had, I could split and get a spectra.


It occurred to me that the DVD I have been using may have been a DVD-R that was burned and published as a DVD. That may explain why It was so easy for me to split my DVD, but there was no purple.


Log in to comment

Although I am having problems with the geometry of the spectrometer, I was able to use a split DVD and get a spectra. No purple.

Once I get my spectrometer working, i will post a bit more of details. I ended up getting some DVD-R also, to insure my problems were related to geometry, not DVDometry, lol, my new word.

spectra_from_DVD_in_open_air.JPG


Log in to comment

Here is a view of my split DVD bottom (clear) and my split DVD-R (purple)
dvd_vs_dvd-r.JPG


Log in to comment

Sign up or Login to post an answer to this question.