DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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Brian Manning made a nice one using a 3" f/15 refractor and my unit which I'm working on now is similar in design. It uses 70mm Celestron refractor.
http://adsabs.harvard.edu/full/1982JBAA...92..112M
There was one build by a high school student written up in Sky and Telescope in the 70's made from two 50mm bino-objectives and inexpensive transmission grating but you really don't want to go smaller then around a 45" fl for the spectroscope section or the width the spectral line is narrower and that requires a narrow slit openning.
For a spectroheliograph used with a webcam, the spectroscope section can be very small. An achromat with about 7" focal length and a 2400 lpm grating would work very well and teamed with a 60mm to 80mm refractor would make for super imaging system.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
Edited by DAVIDG (07/02/09 11:11 AM)
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Charl
member
Reged: 02/08/07
Posts: 84
Loc: Hants, UK
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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.
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Erix
Toad Lily
Reged: 12/25/04
Posts: 22337
Loc: Ohio, USA
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Great read guys. Thanks! A friend just sent me his grating (1200 lines/mm) for a similar project I'm going to be starting soon.
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Erika
Automatic doors make me feel like a Jedi. 
Zhumell 16", 10" LX200 Classic,Orion ED80, ETX70-AT, DS Maxscope 60mm
My CN Gallery * 2007 July - tracking NOAA10963
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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Wow! that is great news Erika.
I think it would be fun to design a less than $100 Spectroscope with a transmission grating and a video camera for making synthetic SHS images.
--------------------
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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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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The nice thing about a 2D detector vs a linear one is that one gets many wavelengths at one time. So in a single image you can have 50 nm or more on each side of the H-alpha line or what ever line you wish Uses software you can then select different wavelengths to turn into a image. This easily allows Dopper studies to be done or image, say the Calcium H and Calcium K lines at the exact same time.
Phil did a first class job on his setup but it is a custom unit with custom software. Free software like IRIS is available to both acguire and process the spectral line AVI movies and make them into a 2D image.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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Quote:
Wow! that is great news Erika.
I think it would be fun to design a less than $100 Spectroscope with a transmission grating and a video camera for making synthetic SHS images.
Piece of cake with money left over! Use this grating from Surplus Shed http://www.surplusshed.com/pages/item/m1541d.html and
two 50mm binocular objectives with about 7" focal length. Surplus Shed has a bunch in the $7, to $10 range and get a hold of a copy "A spectroscope Attachment for Viewing Solar Promincences" by Jack Newton published in the Feb. 1970 Sky and Telescope. The only modification I would do the Newton's design is use a rotatable flat mirror in between the transmission grating and the second bino-objective. The mirror will easily allow one to selection any wavelength they want. Newton's design is fixed for the H-alpha line
If you already have a reflective type grating, you use a the Arectri type layout.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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I can make transmision gratings all day long. For $100 I could easily make 20 2.5 x 2.5" transmision gratings at around 800 lpi. They would fade over time but it would be a cheap way to go. If you cut each piece into 4 gratings you would have 80 gratings for $100. My film goes up to 2000 LPI but that would take some experimentation.
--------------------
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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Erix
Toad Lily
Reged: 12/25/04
Posts: 22337
Loc: Ohio, USA
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Cool! I have a LOT of reading to do before I really dig my fingers into this project. I know I'll need quite a bit of input as the project progresses, so thanks for any advice you guys can give me. 
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Erika
Automatic doors make me feel like a Jedi.
Zhumell 16", 10" LX200 Classic,Orion ED80, ETX70-AT, DS Maxscope 60mm
My CN Gallery * 2007 July - tracking NOAA10963
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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BobH and I are both holographers and used to making very complex gratings. If you need any grating help let one of us know.
--------------------
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: 245
Loc: Berkeley Heights, N.J.
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Quote:
I can make transmision gratings all day long. For $100 I could easily make 20 2.5 x 2.5" transmision gratings at around 800 lpi. They would fade over time but it would be a cheap way to go. If you cut each piece into 4 gratings you would have 80 gratings for $100. My film goes up to 2000 LPI but that would take some experimentation.
But isn't even that higher figure (2000 lpi) inadequate for the intended use here?
Not knocking. Just asking.
I thought that the dispersion of such a grating would be only 1/7th to 1/12th of what you usually need in a spectroscope.
Along that same line of reasoning: I don't understand how the 2400 lpi unit that David G mentioned gives enough dispersion to be useful. Can you (Dave) explain a bit further?
Thanks.
Gene
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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It depends on what order of the grating you are trying to use. If you look at the grating equation and substitute orders 0 through 3 you will start to figure out what happens.
This article is pretty good:
http://en.wikipedia.org/wiki/Diffraction_grating
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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: 245
Loc: Berkeley Heights, N.J.
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Quote:
It depends on what order of the grating you are trying to use. If you look at the grating equation and substitute orders 0 through 3 you will start to figure out what happens.
This article is pretty good:
http://en.wikipedia.org/wiki/Diffraction_grating
No time to read the wiki article yet
but
as you go to higher orders, you lose intensity (unless the grating is blazed to put light into those higher orders) and you get overlap with other orders.
Would the gratings you were talking about be blazed?
Gene
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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No, if I were to make transmision gratings they would be simply black and white sine waves recorded in silver halide materials. I can make them work at different angles. They would not have the efficiency of a blazed grating.
My SHS was designed about a 2400 LPI blazed grating.
--------------------
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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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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You need a grating that has at least 600 lines per millimeter to get enough disperison for the short focal length lens used in a small spectroscope, and used with a webcam. The one I recommended from Surplus Shed has 15000 lines per inch or 590 lines per mm and only cost $15.00
In reflective type gratings, the grooves are cut at a certain angle to concentrate the energy over a certain wavelength range. This is known as the blaze angle. For visual work you want a grating blazed at around 550 nm is which a common. This will allow both H-alpha and CaK images to be taken. If you wanted to do just H-alpha work you can purchased one blazed at 650nm or for CaK work on blazed at 400nm.
If your purchasing a used grating be sure to know the blaze angle. Infared blazed grating are fairly common with a blaze of over 1000nm but when used in the visual they would provide a dim image.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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So my grating must be 2400 L/mm. I choose it from a table from Veio's book.
--------------------
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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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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Quote:
So my grating must be 2400 L/mm. I choose it from a table from Veio's book.
It depends on the focal length of the optics in the spectroscope but the least amount of grooves/mm would be 600 L/mm. Having a 2400 L/mm grating means that the optics can be of shorter focal length to achieve the needed dispersion. The larger the dispersion, the wider the spectral lines which results in wider slit widths. The wider the slit width the more tolerance you have in the mechanics and alignement of the optics to achieve the bandwidth you want.
In a small spectroheliograph, the dispersion needs to be such that the width of spectral lines are at least as wide as a pixel in the camera your using to image them, and having them 3 pixel wide or wider is better for signal to noise.
Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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My fl is 900mm. 90mm at f/10.
--------------------
Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
|
Gene Baraff
sage
Reged: 03/22/09
Posts: 245
Loc: Berkeley Heights, N.J.
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Quote:
I can make transmision gratings all day long. For $100 I could easily make 20 2.5 x 2.5" transmision gratings at around 800 lpi. They would fade over time but it would be a cheap way to go. If you cut each piece into 4 gratings you would have 80 gratings for $100. My film goes up to 2000 LPI but that would take some experimentation.
Then I assume - from the way this thread developed subsequently - that this statement was just a typo: That you had meant to say 880 lpmm and 2000 lpmm, and not lpi?
If so, I withdraw all the questions I had asked when you first wrote this.
Gene
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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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
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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Quote:
Quote:
I can make transmision gratings all day long. For $100 I could easily make 20 2.5 x 2.5" transmision gratings at around 800 lpi. They would fade over time but it would be a cheap way to go. If you cut each piece into 4 gratings you would have 80 gratings for $100. My film goes up to 2000 LPI but that would take some experimentation.
Then I assume - from the way this thread developed subsequently - that this statement was just a typo: That you had meant to say 880 lpmm and 2000 lpmm, and not lpi?
If so, I withdraw all the questions I had asked when you first wrote this.
Gene
That is correct. I can interfer two 532nm laser beams and record the interference as either a reflection or transmision grating. The efficiency on the reflection gratings is quite low. I might be able to hit 30%. By changeing the angles of the laser beams I can vary the spacing. My films thereotical limit is 2000 lpmm. I know people who can make DCG reflection gratings with much higher efficiencies at in shorter wavelengths. I have seen gratings made this way to 8000 lpmm.
My friend Ed wrote this for one of my sites:
http://www.holowiki.com/index.php/Holography_Transmission_Equations_Part_I#Spatial_Frequency
--------------------
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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