color/spectrum measurement equipment

This is a forum to share experiences and ideas about holography.
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Joe Farina

color/spectrum measurement equipment

Post by Joe Farina »

I was wondering what kind of equipment is obtainable (at reasonable cost on eBay, etc.) that can provide a fairly accurate graph of the spectra of light. I have a cheap ($30) diffraction grating spectrascope that's pretty good, but it's not quite accurate enough. I was hoping that something could be found surplus in the range of $200 or less.

I have to get some safelighting in order, and the wavelength needed is around 575nm. I bought some LEDs from China that are supposed to be in the 575-80nm range, but I wanted to get a better handle on this by testing.

It would also be nice to see fairly accurate graphs from the light reflected off objects. I've heard that such devices are quite expensive, but I want to see if anything shows up on Ebay. Thanks in advance for any suggestions.
DJ Mathson

color/spectrum measurement equipment

Post by DJ Mathson »

I am also looking for a spectrograph. The cheapest I´ve seen on ebay have sold for about $500. Maybe you can build one?
Joe Farina

color/spectrum measurement equipment

Post by Joe Farina »

It looks like spectrographs, with a graphical representation of a light sample, are indeed expensive.

I was checking Edmund Scientifics www.scientificsonline.com and saw the "precision economy spectrometer" which looks better than the one I have (I think mine actually cost about $10 at a surplus store). The Edmund one is $40, but they claim 1 nanometer resolution. My scale has 10nm gradations.

There is also another type of spectrometer for testing of gemstones, such as eBay item number 130444014763 called "prism Spectroscope w Wavelength Scale for Gem Testing" for about $95.

The only problem with these types of devices is that the intensity of the wavelengths is very difficult to judge (i.e., just by looking at the intensity of the dispersed wavelengths). This is where the spectrograph would be the instrument of choice, unfortunately they are expensive.
Colin Kaminski

color/spectrum measurement equipment

Post by Colin Kaminski »

You can make your own. You need a grating and some collimation optics. You can make and calibrate a scale with a sodium vapor light. I don't have any good links but solar observers do it all the time. If you just remove the image generator from any spectrohelioscope design you can get a good idea of what you need. There are a bunch of ways to fold the path across a diffraction grating. A good grating is expensive but since you only want to use low intensity light a HOE in DCG would be ideal.

This paper shows all of the ways to use a diffraction grating in a spectrohelioscope. You can skip the text as it is a hard to read style. The equations for dispersion are helpful when you go to calibrate it. Again, the image generators would be deleted making the design much more simple.

http://www.spectrohelioscope.org/net/sp ... oscope.pdf
Joe Farina

color/spectrum measurement equipment

Post by Joe Farina »

Thanks Colin and DJ for the links and information.

DJ, there is one link that looks especially interesting: "Build a high resolution spectrograph in 15 minutes." It looks like a digital camera might be very useful in combination with a diffraction grating spectrometer. I see that the photos can be uploaded on that site for analysis, and a graph created. This looks promising, I will be looking into it.
Joe Farina

color/spectrum measurement equipment

Post by Joe Farina »

I tested the upload function on that site, and it seems to work well. I just used an ordinary digital photograph of an outdoor scene, in .jpg format, uploaded it, and the graph was generated in a few seconds (but I wasn't able to print it, and got a message saying the file may have been too big). There was no calibration on the graph, for some reason.
Joe Farina

color/spectrum measurement equipment

Post by Joe Farina »

After doing some further tests, it looks like a simple spectrograph can be made by using a combination of the diffraction grating/tube design as shown in the "15 minute" spectrograph link, a digital camera, and the upload function of that site for processing the image (or another system for doing the same thing -- there's info. on doing this on one of the other links). But it looks like the particular camera being used needs to be taken into account before designing the grating/tube. My camera was doing some odd things with regards to focusing when I tried to take a picture of the spectrum/scale inside of my spectrometer. It should be fairly easy to calibrate a new scale with the scratchbuilt grating/tube arrangement, by using HeNe for 633 and dpss for 532, that's almost exactly 100nm between them.
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