Foldup Spectrometer for iPhone
I now have two Public Lab fold-up spectrometers working with iPhones. These can take still photos of spectra to be uploaded to SpectralWorkbench.org for analysis, but there is not yet an app that streams video to SpectralWorkbench. The still photos are probably better quality than the video, so that's fine with me.
I made a couple of modifications to the spectrometers. First, I used grating replica polyacetate film instead of a piece of DVD because I have lots of it and it appears to transmit more light (makes a brighter spectrum). This required that the angle of the spectrometer be changed by 3 degrees, which I assume is not necessary if a DVD shard is used [Update: I now think the angle has to be increased by more than 3 degrees]. Second, I made the entrance slit narrower by about 50%. This is easy to do, and allows spectral peaks to be resolved more precisely, but might not be important for many applications.
The video below documents the assembly and adjustments so far.
This research note describes the first field test of the spectrometers.
PDF version
Comments
This is awesome and really helpful! The video is a must see for people building one.
Maybe you could link us to a cheap source of "grating replica polyacetate film" -- or describe from where in the wastestream it can be plucked?
The only relevant waste stream I know of is under my desk where several one inch squares of the stuff are somewhere. I keep dropping them and little pieces are really hard to see. The stuff I bought is here: http://www.scientificsonline.com/diffraction-grating-film-10010.html. You get a lot more than you need, but it must be good for lots of things. You can also buy it in 2" x 2" slide mounts: http://www.scientificsonline.com/card-mounted-diffraction-viewers.html.
Each kind of grating material diffracts light at different angles, so you have to experiment to set up your system at the right angle to get the spectrum centered in the camera image. The 3 degree change I made looks like it is not exactly correct, so more adjusting might be needed. But the iPhone camera is making very useful spectral images.
Chris
It's great to hear that a minor angle adjustment will enable us to use these commercial film gratings. Thanks Chris, super write-up! Also, looks like a lot of folks are reading this, >120 as of my reading.
It looks like 3° of change in the angle is not enough, and maybe 6° is needed for center the visible spectrum in the photo image. But I am a little confused about how I got that wrong the first time around. So some more experimentation is required, and the final angle will depend on whether you want to include NIR.
The video currently has 78 views, 81% from this embed.
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