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Terry Wood

Jupiter (clearer) Nov 5th 2023 w/Mewlon 180c

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Spectroscope diffraction grating (Sale pending)

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SALE PENDING
This spectroscope diffraction grating sold by "Field Tested Systems" is one of the coolest, most interesting accessories I have ever used in this hobby.  The grating is housed like a typical threaded filter and  has 200 finely cut lines per millimeter.  It screws into the bottom of any threaded 1  1/4 inch eyepiece the same as any filter.  I prefer the 200 line over the 100 line grating since it seems to me to provide a more well defined image.   Through the eyepiece you will see a long spectrum of all stars in the field of view.  Brighter stars provide better spectra as will a larger telescope. Spectra can be as long as 1/3 of the field of view though they are usually smaller, though easy to see in detail.  I can get excellent views  of spectra with both my 4 inch refractor and 8 inch SCT.  Like most viewing it takes a bit of time to see all that there is.  Type B and A stars will show dark absorption lines, about 6 or 8, mostly toward the blue end of the spectrum.  Red or orange stars are more spectacular, showing dozens of lines throughout the spectrum with many crowding up near the red end.  You can even see bright emission lines in Wolf-Rayet stars.  To get some idea what the spectra and emission lines look like you can check out Google images of spectra or go to the Field Tested Systems website and click on "Sample Projects."  Of course the better the seeing, the better (more detailed) the spectra and emission lines since they are fairly narrow. Nights of poor seeing will tend to blur out the lines though not the spectra themselves.

For those who would like even better looking spectra and can use a camera, photographing them is easy.  Just turn the eyepiece so the long axis of the spectrum is parallel to the motion of the scope.  Then turn off the clock drive for maybe 10 seconds so the spectrum will be spread out.  Even better, just slow the clock drive so it is almost stopped.  This will provide more light to the spectrum.  The Field tested Systems website has more complex ways of evaluating spectra but I never saw the need to use them. 
This grating is in like new condition.  It was used very carefully.

Price $120.  Seller (me)  will pay shipping.  The price for a new grating is $219.