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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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Quote:
Quote:
My fl is 900mm. 90mm at f/10.
With a 2400 l/mm grating, and 900mm focal length for the optics used in the spectroscope, I calculated that the linear dispersion would be 0.35mm/Angstrom. So if you want a bandwidth of 0.4A, the slit width would need to 0.14mm or 0.0055 inches. That is not difficult to do.
- Dave
Thank you Dave! That was my next project before I had to move. I am hoping to make an adjustable slit. I have some old veneer heads laying around. Now I just have to rebuild my metal shop. I think it will be a year before I can do ATM projects inside again. I have 3 of the objectives. I also have some prisms to make rotating slit motion. I never found the ones from old movie projectors so I am going to have to glue up some normal prisms. 4 sides will give me a start. If I find some old projector parts I can redesign later. I keep looking on Astromart for a large flat for a heliostat bu so far I have net seen one and had the money at the saem time.
--------------------
Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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Gene Baraff
sage
Reged: 03/22/09
Posts: 246
Loc: Berkeley Heights, N.J.
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Quote:
I can interfere two 532nm laser beams and record the interference as either a reflection or transmision grating.
I had wondered if this was what you were doing but didn't ask because I thought that doing so would highjack the thread.
Gene
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nytecam
Postmaster
Reged: 08/20/05
Posts: 5748
Loc: London UK
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Quote:
Before Hale built the SHS he built the SHG or spectroheliograph which I believe in some configurations did scan the image by turning the drive off. Other models by him, and Deslandres in France, scanned with a moving slit.
Try ATM - Scientific American 1933; p180-214; Solar research for amateurs/ Hale's spectrohelio-scope/graph detailed drawings/photos -if dated by today's standards.
My spectrohelioscope had a fl of 900mm and used a single large lens segmented for both primary OG imaging the sun and auto-collimator [eg spectroscope] with 600 l/mm grating ruled by Brian Manning showing the idea/article at http://www.astroman.fsnet.co.uk/optics.htm
I recently sold the grating for a new SHS project. 
--------------------
Nytecam 51N 0.1W
Meade 30cm LX200+ETX-70+e-finder+C8+Ha+CaK PSTs SBIG SGS+homebuilt spectrographs
Starlight SXVF_M9+Lodestar CCDs/Canon 300D DSLR/Fuji E550
My observatory build-ETX-70 imaging-my videos
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AlienFirstClass
professor emeritus
Reged: 02/13/09
Posts: 738
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Could someone discuss what type of surplus equipment one could salvage parts from for solar instruments?
Lens?
Sensors?
Gratings?
For an example...I have several surplus diffraction gratings...how do I determine if they are suitable for solar instruments?
Thanks
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AlienFirstClass
professor emeritus
Reged: 02/13/09
Posts: 738
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Quote:
Another way to capture the image from a SHG is to replace the second slit with a linear CCD array as done here by Philippe Rousselle.
Monochrome linear CCD arrays are readily available for next to nothing, I salvaged this one from a bar code scanner.
Could discuss more as to where to get arrays in surplus electronics?
Thanks
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AlienFirstClass
professor emeritus
Reged: 02/13/09
Posts: 738
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Quote:
Quote:
Quote:
My fl is 900mm. 90mm at f/10.
With a 2400 l/mm grating, and 900mm focal length for the optics used in the spectroscope, I calculated that the linear dispersion would be 0.35mm/Angstrom. So if you want a bandwidth of 0.4A, the slit width would need to 0.14mm or 0.0055 inches. That is not difficult to do.
- Dave
Thank you Dave! That was my next project before I had to move. I am hoping to make an adjustable slit. I have some old veneer heads laying around. Now I just have to rebuild my metal shop. I think it will be a year before I can do ATM projects inside again. I have 3 of the objectives. I also have some prisms to make rotating slit motion. I never found the ones from old movie projectors so I am going to have to glue up some normal prisms. 4 sides will give me a start. If I find some old projector parts I can redesign later. I keep looking on Astromart for a large flat for a heliostat bu so far I have net seen one and had the money at the saem time.
Could someone discuss what suitable parts from projectors will work for a SHS?
Thanks
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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The best explanation of how a SHS works is to look up Fred Veio's book. I am going to over simplify here a little. The idea is you sweep a slit past an image of the sun and bounce it from a diffraction grating. You then sweep another slit across the spectrum at the same rate. There are quite a few ways to do this in practice. One is to take the rotating prisms from an old movie projector. I have seen some large 8 sided prisms that would spin inside a projector. With two of them you can use them to sweep an image by a stationary slit.
This mechanical task is the key to making a successful SHS. I have seen at least three different ways of doing it but I am sure there are many more. It takes a fair amount of planning to make it all work.
You can measure your diffraction gratings by bouncing light of them and measuring the spectrum. If you bounce white light off it and project to a white card a know distance away you can you the dispersion equation to calculate a rough estimate for the grating frequency. If you want to know exactly you can use a sodium light or something else that you can know the exact frequency of the lines. Then if you know the distance between two lines and the distance from the grating to the projection screen you can calculate the spacing. This will not tell you the efficiency however.
--------------------
Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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