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Killer deal on USB spectrometer! (update: legitimate!)

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Has anyone tested the accuracy over the entire visible spectrum?

I improvised a spectrometer with a portable spectroscope and a webcam, tried it out with the theremino software (same thing they use) and it was reasonable on the blue-green range (+-3nm), but way off on the reds (639nm on a HeNe, 700nm on a 685nm). I calibrated it with the default 436 and 546nm lines of a fluorescent lamp. I'm suspecting all it does is a linear fit using those two points, which will give incorrect results because the rainbow from a grating isn't linear at all.

I'm wondering if this also happens with their device.
 
Atomicrox said:
Has anyone tested the accuracy over the entire visible spectrum?

I improvised a spectrometer with a portable spectroscope and a webcam, tried it out with the theremino software (same thing they use) and it was reasonable on the blue-green range (+-3nm), but way off on the reds (639nm on a HeNe, 700nm on a 685nm). I calibrated it with the default 436 and 546nm lines of a fluorescent lamp. I'm suspecting all it does is a linear fit using those two points, which will give incorrect results because the rainbow from a grating isn't linear at all.

I'm wondering if this also happens with their device.
Click to expand...

This is a question that has been puzzling me since I heard that these were calibrated using only two lines. I don't see that it is possible because, like you said, the spectrum from a diffraction grating is not at all linear. But, with only two lines, one can only get a linear relationship.
 
I am back for more updates.
Yes, I was told that the plastic stuff is the slit, it is printed, it seems.
It is not a very good idea to shine the laser directly to the spectrometer. it is better to make it reflect on a wall or a paper and then analyse it.

We spent a very nice trimester with out student working on those spectrometers. They are very handy and educational (pedagogical)
they are really worth their price.
I hope that they will have some more upgraded spectrometers as they promized few months ago, but no one for now.

regards
 
Civitus said:
I am back for more updates.
Yes, I was told that the plastic stuff is the slit, it is printed, it seems.
It is not a very good idea to shine the laser directly to the spectrometer. it is better to make it reflect on a wall or a paper and then analyse it.

We spent a very nice trimester with out student working on those spectrometers. They are very handy and educational (pedagogical)
they are really worth their price.
I hope that they will have some more upgraded spectrometers as they promized few months ago, but no one for now.

regards
Click to expand...

Civitus, did you test the accuracy over the entire visible spectrum?

I improvised a spectrometer with a portable spectroscope and a webcam, tried it out with the theremino software (same thing they use) and it was reasonable on the blue-green range (+-3nm), but way off on the reds (639nm on a HeNe, 700nm on a 685nm). I calibrated it with the default 436 and 546nm lines of a fluorescent lamp. I'm suspecting all it does is a linear fit using those two points, which will give incorrect results because the rainbow from a grating isn't linear at all.

I'm wondering if this also happens with their device.
 
Hemlock_Mike said:
DDEN -
It would be nice to try another program but I suspect that the Ithing
does its own processing. I'd like to know.
HM
Click to expand...
Dear Hemlock,
As i am regular user of the spectrometer for my classes, I am in touch with the guy of ThunderOptics
Now, they have a new software that I have used also, it is just WONDERFUL
it is Spectragryph, done by Friendrich a renewed scientist


http://www.effemm2.de/spectragryph/license.html

Enjoy
Civitus
 
Does that program allow you to calibrate properly (i.e. using 4+ known lines)?
 
It's cheap, but for some of us, that plus or minus 3 nm isn't accurate enough. It's that small amount of difference we would want to measure, unable to do so with that wide of an error range isn't useful. We can already guess our laser diodes are plus or minus less than that much just by the part number.
 
I contacted ThunderOptics about this spectrometer and they state that it is possible to calibrate it to an accuracy of less than +/- 3nm.

Many thanks for your interest in our products.
Yes, the spectrometer can meaure the wavelength of lasers, and the accuracy depends mostly on the calibration you will do. but, for sure, you can go lower than 1nm.
The only point I am worried is about the intensity of the laser, may be it can saturate the CMOS detector. For this, It may be better to contact directly our webpag for the technical details.
Please, if you have any other question, don"t hesitate to contacte us again.
All the best
Amayas
Click to expand...

Now, how would I go about calibrating one if I decided to get one?
 
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It may be "possible", but seems unlikely. For $70.00 you can't expect anything approaching a professional spectrometer. Unless you are fine with the inherent inaccuracies, I'd stay away from this homemade hobbiest item. The propensity to drift has to make this thing only good for, at best, a wide margin for error.
 
I've seen these before and they are set up by using two points of reference. Because the diffraction grating, or prism, is not linear, this cannot work properly. It even looks like something someone threw together.
 
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