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 Post subject: Beck spectroscope
PostPosted: Fri Mar 14, 2014 4:31 pm 
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We just got our Beck prism unit back online but see a ton of horizontal lines that all but obscure the spectra. Probably dirty but I am concerned about how far I should go taking this one apart.
Anybody have any ideas?
Thanks

Jim


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 Post subject: Re: Beck spectroscope
PostPosted: Mon Mar 17, 2014 2:47 pm 
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Horizontal black lines across the spectrum would indicate an entrance slit with very dirty edges. Try sliding a toothpick up and down each slit edge to remove the gunk.


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 Post subject: Re: Beck spectroscope
PostPosted: Tue Mar 18, 2014 10:48 am 
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Thanks for the response. I thought I had it all cleaned but got a Rolex special cleaning tip and it appears much better. One more thing...there is a vertical calibration line at 5890 in the actual spectra display below the scale. Many reading seem to bee off exactly 1000nm. Is there a calibration mode for this unit?


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 Post subject: Re: Beck spectroscope
PostPosted: Thu Mar 20, 2014 2:12 am 
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There is an adjustment screw on the head of the unit in the block that you look in.
It adjusts the location of the wavelength scale. You need a real sodium light to look at. A low pressure sodium light. The high pressure sodium lights that are so common are useless for this purpose. They have a broad absorption band at 589 rather than the double D line.

I looked at Barbra's Beck and it sounds like you have a similar wavelength scale prism model. On her's the calibration screw was locked down with a "jam nut" .
In the arrangement the screw is turned until the double D line from the sodium light is split by that tall tick mark. Then without letting the scale move the jam nut is "jammed" tightly to lock the scale holding thread into position. WITHOUT letting it move which is a good trick. It is such a good trick that when they adjusted Barbra's they locked it so tightly that I could not move it , with any force I was willing to apply to an instrument I did not own personally. Furthermore , the jam nut was not a hex shaped nut but a special custom made nut from the Beck factory , where their assemblers had the special custom made wrench that allowed them to turn the jam nut. Probably a piece of brass tubing with a t handle and an inside diameter big enough for the screw driver. Look for a round nut with four slots. That is the jam nut and it is on the wavelength scale adjusting screw.
They also may have put Loctite or lacquer or other locking compound on the two screws.

The good news MAY be that since your wavelength scale is off by so much someone may have broken that screw loose.

You could calibrate with a sodium interference filter. But these are very temperature dependent. A real low pressure sodium lamp is as invariant as anything commonly encountered in this world.

You can find them lighting "U-Store It" lots. They are very monochromatic yellow.
Just take your spectroscope there at night and line it up.

You can lock the jam nut (aka locking nut)with a toothy hemostat.
http://en.wikipedia.org/wiki/Jam_nut
http://www.boltscience.com/pages/twonuts.htm


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