Attempt at Distance Spectrometery
I was attempting to see if I could detect a sample light source at a distance (I know astronomers can do this to determine the elemental makeup of distant stars). I attached an old rifle scope and my spectrometer to a piece of plywood, balanced it so I could mount it on a tripod and added a short length of tubing to act as a spotting (aiming actually) scope.
Unfortunately, the amount of light coupled into the spectrometer was not sufficient to register a reading. If blast a laser pointer into the end of the scope, the webcam registered a small amount of light, but apparently the slit blocks enough of the available light to prevent a useable reading of streetlamps and sun illuminated objects during the day..
Does anyone know the specs of the webcams in the kick-starter spectrometers? I'm interested in the minimum light required for an image measured in lux. I am hoping that a camera with better low light performance might work in this application.
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I think you're right -- and for many applications, we're going to need to do long-exposure imaging. If we can iterate and find a good camera, perhaps we can negotiate a deal and upgrade for the next major release of the kit, to broaden its abilities.
You can simplify this by using a single lens instead of the scope. Attach something white to either side of the slit and then focus the object you want to examine on that white background near the slit(or temporarily cover the slit with a piece of paper while focusing). The smaller the f number of the lens the brighter your image will be. To start, it would be best to focus a light bulb on the slit. You can start with just a magnifying glass if you like. This is likely to give you much greater intensity on the slit than the rifle scope and is cheaper to boot. If you are satisfied with the result, then substitute a lens that is corrected for chromatic aberration (an achromat) for the magnifier. If you have a lens from a single lens reflex camera around that would be great.
I was amazed to see this problem solved by Astronomical Spectroscopy with Modified Webcams (now THAT'S distance spectrometry!) They are using a CCD based webcam with <1 lux sensitivity. I was unable to find any lux ratings on webcams listed on Alibaba.
I was just playing around trying to identify streetlamps. What other useful things can be measured at a distance?
Useful thing to measure at a distance: Flame-offs at refineries and factories. Try to see what they're burning off! If it's at night, it could be illegal and they're just hoping no regulators (or DIY scientists with distance spectrometers) are watching. And the burn itself might give good emission lines...
This is SUPER exciting!
I conjecture that you just have an alignment problem. My suggestion would be to fix the laser and scope alignment and then move the spectrometer around to get maximum reading.
Another method just occurred to me. Remove the scope and firmly attach the board. Hot melt glue would be a good choice. Point the laser from the end of the board into the spectrometer and adjust the angle until you get the maximum reading. Trace the angle of the laser onto the board. I suspect that the angle is not straight down the axis of the spectrometer. At this point you have a better probability of aligning the scope properly.
Thanks for the thoughts Tom.
I got a 4" magnifying glass at the dollar store (2x magnification) and mounted it in a shoebox. I was able to determine the focal distance from the lens with a sheet of paper (11 1/2"). When aimed at a streetlight, I can focus the light's image on the spectrometer's aperture slit, but unfortunately have not had success at getting a reading. This set up is terrible for getting optimal alignment as everything has to be hand held at the moment.
On the bright side, I can successfully run two 10 foot USB extension cords from my PC to the spectrometer.
Pictures are not posting for me, but here's what it looks like:
http://www.flickr.com/photos/zombiedetector/8444145588/
Be sure to check out Scott E's questions here: http://publiclaboratory.org/notes/eustatic/2-3-2013/distance-spectrometr...
I replaced my spectrometer with a Logitec C310 (5MP) webcam with a DVD-R+ section taped over the lens. The 4" magnifying glass was able to focus high pressure sodium street light about 150 yards away onto the lens and get a reading. The process took two people, one to aim the shoebox till the focused dot of light fell on DVD-R+ covered lens and the other person to capture the image. The reading is uncalibrated and not focused at all, but I DO see a spike at around 575nm indicating sodium.
http://spectralworkbench.org/analyze/spectrum/3631
Embedding in the above spectrum 3631:
Lots of noise indeed, but i do see the spike. Did you manage to take a baseline too?
I think we need tripods! :-)
No, I didn't take a base line. Last night's measurement was a quick and dirty proof of concept. There are plenty of places this can be improved:
Web Cam Focus - How did you determine where to set the focus distance on the orginal spectormeters? I can change the focus by moving the 4" magnifying lens as well.
Diffraction Grating - I read the DVD-R+ grating blocks more light than a commerical 1000/in. grating. I've ordered a 6 x 12" sheet to experiment.
Alignment of Parts - The lens and spectrometer need to be aligned and focused for each measurement. Firm mounting (hot melt glue, etc) in a solid body (ABS Tube) may be sufficient for alignment, but we need a focus ring (screw on ABS cap?)
Tipod Mounting - A solid body needs to be balanced with a mounting nut to be supported by a strong tripod.
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