This is a testing site only. See the live Public Lab site here »

Question: Question: More of a comment, really

bowlerhatman is asking a question about spectrometry
Follow this topic

by bowlerhatman | August 09, 2014 09:11 | #11027

Hi there, I'm interested in building one of these for use in my homebrewery, but I have found that many of the links seem to be broken (the one to the pdf of the cardboard insert, and the old instruction manual, for instance). I'm also a little unsure about dimensions, as nothing seems to have a measurement attached to it other than the focal length of the webcam for the grey box camera desktop version. It says 9 inches, in order to focus on the slit, yet the slit (based on my estimation) is much less than 9 inches distant from the webcam. I can't tell, however, whether I'm missing some element of the optics, or whether my estimate is just terrible.

I guess, in short, I was wondering if someone could make accessible a clear and concise list of critical dimensions, and fixx the broken links.

Thanks, Frazer.


Thanks for helping out, Frazer - can you list which links are broken and on which pages? I hope it's a simple URL change...

The PDFs should be scaled -- you're right, we should include more dimensions, but if you print them at letter size, they should be to scale!

Is this a question? Click here to post it to the Questions page.

Reply to this comment...

Hi Warren, the links that I have found not to work are both on the page at:

They are: "grey box" 2.0 version: desktop-kit-instructions-0.4.pdf (200 kB) Insert for cutting out of stiff matte black card paper:

Scaling is good, but I'd also like some more information on how one arrives at the numbers, as well as just the number. For instance, if the scale I gauge by sight is right, why is it that we focus the camera at 9 inches so it focuses on the slit, even though the slit is less than 9 inches away from the camera? Does the diffraction grating significantly alter the focal length? Or are we trying to focus on some point beyond the slit? I suppose I'm after some more technical details about the workings of the machine, rather than just relying on correct scaling. Not that the scaling you provide is bad, I'd just like to understand better.

Is this a question? Click here to post it to the Questions page.

Reply to this comment...

OK, i think i fixed the links - sorry!

The 9" is a long story -- there's some good info on it here:

however most of the measurements were arrived at empirically and experimentally, to tell the truth! See:

Reply to this comment...

Awesome, both links are fixed, thanks.

Thanks for the info on the angles and grating, I appreciate it.

Reply to this comment...

Just stumbled upon this in checking out the questions feature. Not sure if you've seen but there has been some prior work done in this area:

Reply to this comment...

Log in to comment