multiple object spectrographic telescope
Posted: Wed Dec 04, 2019 8:01 am
this concept looks interesting.
https://www.youtube.com/watch?v=ollpNYOrbcc
http://www.3dewitt.com/telescope/slide1
I have tried a little duct tape mockup using my L200 and an input lens after the objective grating, looking into the output port with an eyepiece, I can see the image of the scene the input lens is looking at, but with a spectrum overlaid. That is, each colour is mapped to a different spatial coordinate in the input image.
http://www.3dewitt.com/PDF/3DeWitt_Dittoscope-NIAC.pdf
My next plan is to build a neater setup with the biggest gratings I have (a 150mm x 75mm piece of 1000lpmm grating) as well as a couple of other 50x50mm reflection gratings I have.
Then I'll try to get a long piece of transmission grating film (150mm x 2000mm x 1000lines/mm.) and set it up as a shallow (grazing) EXIT angle objective grating in front of my 200mm f6 (stopped down to 150mm), with the L200 downstream (it has a 600lpmm grating.) I will post results and further investigations.
It's ingenious: the long, grazing angle objective grating maps a separate direction to each of the separate wavelengths for a single exit direction (which is selected by the telescope via input slit of the L200 littrow spectroscope). Multiple directions are therefore all mapped to the input slit of the spectroscope, but for each direction, only one colour arrives at the slit. The output of the spectroscope is then a spatial map with only one colour per direction.
To get full spectra for each star, drift scanning is required. this doesn't seem much of an avantage over a normal slit spectroscope. But the advantage is that due to the grazing exit angle, flatness tolerance on the objective grating is apparently relaxed (not sure that I agree, as what about the input angle of the objective grating also?), so large, thin, low specification plastic film gratings can be used as the primary collector. The proposal was to scale it up to a huge scope.
Has anyone else ever seen this sort of double dispersion (both before the telescope, and simultaneously in the usual location after the slit) before?
I think it's worth some further investigation.
https://www.youtube.com/watch?v=ollpNYOrbcc
http://www.3dewitt.com/telescope/slide1
I have tried a little duct tape mockup using my L200 and an input lens after the objective grating, looking into the output port with an eyepiece, I can see the image of the scene the input lens is looking at, but with a spectrum overlaid. That is, each colour is mapped to a different spatial coordinate in the input image.
http://www.3dewitt.com/PDF/3DeWitt_Dittoscope-NIAC.pdf
My next plan is to build a neater setup with the biggest gratings I have (a 150mm x 75mm piece of 1000lpmm grating) as well as a couple of other 50x50mm reflection gratings I have.
Then I'll try to get a long piece of transmission grating film (150mm x 2000mm x 1000lines/mm.) and set it up as a shallow (grazing) EXIT angle objective grating in front of my 200mm f6 (stopped down to 150mm), with the L200 downstream (it has a 600lpmm grating.) I will post results and further investigations.
It's ingenious: the long, grazing angle objective grating maps a separate direction to each of the separate wavelengths for a single exit direction (which is selected by the telescope via input slit of the L200 littrow spectroscope). Multiple directions are therefore all mapped to the input slit of the spectroscope, but for each direction, only one colour arrives at the slit. The output of the spectroscope is then a spatial map with only one colour per direction.
To get full spectra for each star, drift scanning is required. this doesn't seem much of an avantage over a normal slit spectroscope. But the advantage is that due to the grazing exit angle, flatness tolerance on the objective grating is apparently relaxed (not sure that I agree, as what about the input angle of the objective grating also?), so large, thin, low specification plastic film gratings can be used as the primary collector. The proposal was to scale it up to a huge scope.
Has anyone else ever seen this sort of double dispersion (both before the telescope, and simultaneously in the usual location after the slit) before?
I think it's worth some further investigation.