Wanted: any information on this spectrometer - Page 1
Forum section: electronics / general

author: TerraHertz
author_rank: Super Contributor
timestamp: July 28, 2015, 07:06:08 am
content: This is a spectrometer I bought years ago, and it's been sitting on a shelf ever since. Now trying to get it going. No electronics, purely an optical device.The primary problem is my ignorance, and a missing component. Which wouldn't be problems, if I could find any information at all on this unit. But so far, a total blank. What I'm after is a user manual specific to this, or even a text that discusses the setup and use of this type of basic instrument in general.It's a simple thing, perhaps intended for school use. Two telescopes on separate pivots, one with an adjustable slit at the outer end and a converging lens at the inner end. The other telescope with an inner converging lens, and an eyepiece like from a microscope at the outer end. Lining them up, there's no problem resolving the far end optical slit.The idea is that the center stage holds a prism or diffraction grating, and the eyepiece is swung around to examine portions of the optical spectrum.Should be simple, but can I get it set up right? No.It was sold and came as in the 2nd pic. (Minus the dust covers.) Apparently used a little, and someone had lost the upper styro packing, any original manual, and whatever it was supplied with for a diffraction grating. I later bought the small prisms in the pic.There's a label saying BRAGG & CO. But I can't find any such instrument maker. Only real estate agents, etc.With the standard of manufacture, I'd suspect it was made in China or Hong Kong, maybe in the 1980s through 2000.Does anyone know anything about this kind of thing? Even a URL of a forum where people might, would help.It's a toy really, but a nice basic spectrometer to start with. I also have a cute little jeweler's spectrometer, but it has no scale. And two lab-grade but old Shimadzu QV-50 spectrophotometers, but those will take a fair bit of work to get running and automate.

author: helius
author_rank: Super Contributor
timestamp: July 28, 2015, 07:16:10 am
content: If memory serves, the direction light bends is reversed for a prism compared to a diffraction grating. So simply substituting one for the other is not going to work.

author: Isad
author_rank: Frequent Contributor
timestamp: July 28, 2015, 07:18:14 am
content: This might help idk if you have google anything but this is a site i foundhttp://pe2bz.philpem.me.uk/Lights/-%20Laser/Info-902-LaserCourse/c10-01/Module10-1.htm

author: TerraHertz
author_rank: Super Contributor
timestamp: July 28, 2015, 08:32:02 am
content: Quote from: Isad on July 28, 2015, 07:18:14 amThat's quite useful! But in a way confusing, since the setup they show is exactly what I'd expected to work and was trying, with no luck.I think my fail was a combination of insufficiently strong light source, prism a bit smaller than the optical path diameter so there's extraneous light, and generally too much light everywhere. May need to make a dark cover for it.Mainly though, I gather a diffraction grating would be better than a prism. But what kind, line spacing, etc?

author: DTJ
author_rank: Super Contributor
timestamp: July 29, 2015, 03:29:20 am
content: Try posting on Usenet newsgroup sci.electronics.designLook for a guy called George Herold, I think his main job is designing instruments and training aids for physics laboratories.There are also a bunch of other guys there with similar backgrounds.He seems to be a well informed & approachable guy - he may know what you want to know or may be able to tell you who made that instrument.

author: Someone
author_rank: Super Contributor
timestamp: July 29, 2015, 06:30:55 am
content: http://www.redtorope.com/calcs/diffraction/For a reflective grating a typical 600 lines/mm grating should provide a good balance for visible light in the first order operating it with a 30 degree incidence angle. You could try and find a specialised grating with a blaze and profile designed for a high angle of incidence with 1200 lines/nm or more, or higher orders.

author: TerraHertz
author_rank: Super Contributor
timestamp: July 30, 2015, 01:22:18 am
content: Thanks, DTJ and Someone.(Edit: Yes, I made a spelling mistake in that.)

author: bradleytron
author_rank: Regular Contributor
timestamp: August 08, 2015, 04:32:32 am
content: These are old optical spectrometers for looking at emission spectra. The instruments were essentially used in undergraduate teaching labs (physics) for introductory instruction on the subject of optical spectroscopy. The circular platform should rotate and the idea is that you mount a large prism (or transmission diffraction grating). Into this and through one of the telescopes (should be equipped with an adjustable slit) you project the emission spectra of a gas discharge tube; He, Ne, H and so on. Pasco scientific used to sell these. Along two sides of the platform assembly you should have two precision verniers. Looking through the other telescope, at the dispersed spectra, you will see a series of bright lines. These lines define the spectra (wavelength's) characteristic of the gas being studied. The viewing telescope should have a cross hair which you can use align with various lines and each line, relative to others, will have a corresponding angular displacement that you can read on the vernier dial. If you calibrate these displacements with a known source, then you can replace that with an unknown source and hopefully identify the gas producing the spectra.Hope this helps. I'll dig around and see if I can find any old documentation.

author: dexters_lab
author_rank: Unknown
timestamp: August 13, 2015, 03:26:56 pm
content: i have a small diffraction grating here, maybe you could make use of it? it has a small scratch on it and is a little dusty () but if your just toying around with it then it'll be fine.it's about 55x55mm, 1200 lines/mm, blaze at 12.1 degreescame out of large perkin elmer spectrometer i took to bitsif the postage to Oz is not much i can send it to you free