Public Lab Research note


The accidental raspberry pi spectrometer: first light

by khufkens | April 29, 2015 02:28 | 135 views | 2 comments | #11774 | 135 views | 2 comments | #11774 29 Apr 02:28

Read more: i.publiclab.org/n/11774


I put my design together today. The design used is shown below, but has some issues still. General layout: slit on the left, baffle and grating / sensor array on the right.

A first spectrum can be found below.

Accomplished:

  • Seems like the incident angle was pretty much perfect, aligning the red part of the spectrum to the center of the image
  • the sensor array setup works nicely (compact unit)

Issues:

  • focus, had to mess with the raspberry pi camera lens
  • I didn't calculate the needed distance between the grating and the sensor as to maximize the used pixels (I admit, I was lazy). The small exit angles of the 300l/mm grating require a large distance from the grating to expose the whole image sensor. The peak at 0 nm is the 0th order peak, the little peaks > 1000nm are the second and third order peaks which also make it onto the sensor.

Lessons learned: do the math before making a design.

Back to the drawing board, more later...


2 Comments

Can you let me know how you focused your camera? I just finished my spectrometer yesterday; I can take spectral images at this point, but they need to be tuned up a bit. Is there a video you can refer me to, or some web page that can help me get my camera in focus?

Thank you!!

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On the raspberry pi camera there is no real focus, so you either unscrew the lens assembly (google macro lens / macro photography and raspberry pi camera) or you buy a pi camera with a different lens mount which allows for better focus control. I've discontinued the project so you won't see any finished product I'm afraid. Due to good detective work I don't need the spectrometer to characterize the raspberry pi sensor no longer.

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