A very preliminary test of resolution

A project log for OtterVIS LGL spectrophotometer

A super cheap decently resolving open source VIS-spectrophotometer. The cheapest in the OtterVIS line.

esben rosselesben rossel 06/06/2016 at 20:222 Comments

I recently acquired a few good laser pointers in a collecting frenzy:

My five new better quality laser pointers.

I can't use all of them for work at the same time, so I figured I would try and see what kind of performance I can expect from the OtterVIS LGL. After carefully focusing an improvised slit with two razors taped on a piece of cardboard, using a mirror for autocollimation, I learned the box is 3 mm too short. But I also got this:

These are the two reds. There are roughly 15nm between the two lasers. It's not as easy to see the red lines compared to the green ones below, I guess the camera's Bayer filter has a part in this.

The two green lasers. They are app. 12nm apart. As you can see there's better resolution at lower wavelengths.

The results are better than I expected. Of course this not proof of the resolution of the spectrometer, but it leaves me optimistic. I've done no effort to focus the diffracted light, and I've not done any readings with the CCD.

Right now I'm speculating if some clever use of Scheimpflug principle can improve the separation in the red part of the spectrum.


xof wrote 06/11/2016 at 17:12 point

You don't need lasers to evaluate the resolution.   Compact fluorescent lamps  offer 2 (mercury) yellow spectral lines 2.1 nm apart (577 & 579.1 nm).  Sodium doublet is (yellow-orange) 589 & 589.6 nm.  In the Sun spectrum, you also have a magnesium green triplet (518.4, 517.3 & 516.7 nm) and a lot of other Fraunhofer lines .

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esben rossel wrote 06/12/2016 at 05:25 point

Thanks, that is excellent advice. I'll keep it mind for the real test later :) I used the lasers because: 1 I had them lying around and it was easy. 2 I wanted something I could photograph.

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