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question about H-alfa filter

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#26 DAVIDG

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Posted 12 November 2012 - 01:07 PM

Philip,
Nice work and glad to hear the new filter is working well. I found on my unit that if I polish the occulting cones to a mirrored finish and then blacken just the very edge of the cone that I didn't get any stray reflections.
Does you unit have an adjustable iris in the light path between the first lens which the cones is attached and the second rear relay lens ? If not installing one will also help in removing any stray reflections.
Are you able to offset the eyepiece so you can place the edge of the cone with a prominences visible in the center of the field of the eyepiece ?

- Dave



#27 philipdo

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Posted 12 November 2012 - 01:07 PM

Thanks Highfnum,

all I did was restore the coronagraph. It was originally built in the early eighties by Belgian/French amateur Dany Cardoen, founder of the Puimichel observatory in France. He quickly turned professional and makes optics for ESA, ESO and other institutions.

#28 philipdo

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Posted 12 November 2012 - 01:12 PM

Thanks Dave,

blackening the edges of the cones seems like a good idea, especially since I already blackened other surfaces (lens edges, lens mountings...). I have already added an adjustable iris diaphragm. There is no provision for offsetting the eyepieces. I'm tinkering about the construction of a simple excenter to take care of this.

#29 nytecam

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Posted 13 November 2012 - 03:39 AM

Thanks Phil and Dave - I bow to your superior knowledge and experience. I was being over cautious on coronagraph optics :bow:

I visited the late Horace Dall's rooftop workshop many decades ago with all his wonderful gear including his Promscope with solar occulting disk and wideband H-alpha filter but didn't view through it as it was cloudy ;)

David/Phil - could you clarify - is a 'Coronagraph' for viewing the solar corona [with a coronal line filter under exceptionally clear skies] or does the term extend to the chromosphere and H-alpha phenomena :question:

#30 DAVIDG

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Posted 13 November 2012 - 09:13 AM

Nytecam,
One of the references I used when building my coronagraph/ promscope was an article by Horace Dall. The optics in a Promscope and Coronagraph are the same. The design was invented by Lyot. The problem with viewing the corona is that it requires very clear and scatter free skies hence the need to observe on of a top of mountain or from a ballon, even with a narrow band filter. When you add a narrow band H-alpha interference filter, one can now observe prominence will less then ideal sky conditions because the Lyot optics greatly reduce the scatter and the filter does the rest and also the fact that the prominence are very bright at the H-alpha wavelength. Under very favorable conditions one can observer prominences using a coronagraph with just a simple red glass filter.

- Dave

#31 philipdo

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Posted 13 November 2012 - 12:47 PM

@Nitecam
As Dave said. Perhaps with one exception: it is easier to see the corona during a total eclipse, since we are in a rather large shadow cone, with no diffraction or scattering at all. Even the best constructed coronagraph barely covers the solar disk, causing small amounts of light scattering. The corona is hard to see because the chromosphere (with prominences) has an intensity about 1,000 times less than the the surface of the sun (photosphere). The corona has an intensity of 1,000 less than the chromosphere...

@Dave
I solved the excenter problem, not by building an eccentric mechanism, but by making an eccentric eyepiece. When I turn it around in the eyepiece holder, I am able to scan the entire limb of the sun with a magnification of about 130.

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#32 DAVIDG

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Posted 13 November 2012 - 01:26 PM

Philip,
I was going to sugguest something very similar. Great job on your eyepiece and on the restoration of your coronagraph.
One of my farther modifications to my unit will some day be to add a filter wheel so I can observe the prominences in different wavelengths like the H-Beta, CaK and Helium D lines. The problem is finding the filters of narrower enough bandpass for those wavelengths.
I'm restoring an orginal Hale spectrohelioscope, exactly like what is pictured in ATM-1 so I hope to have it working soon so I can observe the Sun in any wavelength I wish.

All the Best,
- Dave

#33 philipdo

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Posted 13 November 2012 - 01:48 PM

Dave,

how did you find such a fine instrument as a Hale spectrohelioscope? Any pictures?

#34 highfnum

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Posted 13 November 2012 - 03:46 PM

"but by making an eccentric eyepiece"
oh so clever - I gota make one of those!

philipo - yopu gotta get a baloon and get uo to about 60K feet :lol:

#35 philipdo

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Posted 13 November 2012 - 04:52 PM

Highfnum,

60K feet...Do you think the scope would qualify as airplane hand luggage :lol: ? For the eccentric eyepiece I used a singlet lens. There is no need for a wide field, since the eyepiece lens is almost nested against the inner wall of the barrel, thus already restricting the field of view.

#36 highfnum

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Posted 13 November 2012 - 06:55 PM

"I used a singlet lens." what dia and F.L in mm plz

#37 philipdo

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Posted 14 November 2012 - 09:46 AM

appr. 8 mm diameter and 10 mm FL

#38 DAVIDG

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Posted 14 November 2012 - 10:20 AM

One of the ways I was thinking of making eccentric adapter would be to use a 2" focuser and then make a 2" diameter plug that fits in the focuser and drill an 1.25" hole off center Then one could use any eyepiece you wish and rotate the plug with the eyepiece to view and area around the limb of the Sun.

- Dave

#39 DAVIDG

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Posted 14 November 2012 - 10:38 AM

Dave,

how did you find such a fine instrument as a Hale spectrohelioscope? Any pictures?


The spectrohelioscope was installed in the Cook Observatory not to far from me. Here is a link to a PDF that shows the instruments installed at that observatory including the Hale spectrohelioscope that I'm restoring. It was then given to the University of Penn and after many years they no longer wanted it. Some of parts are missing. My good friend Matt Considine located it and the University of Penn asked he if would like it. Matt and I retrived it on one of hottest days of the years, a few year back from the 5th floor of the Physic building. Matt has donated it to Springfield Telescope Makers were it will be installed at Stellafane. Here is a link to a YouTube video that Matt gave about it and the plans to locate at Stellafane. http://www.youtube.c...h?v=XrfdLIPSC34
I'm in the process of restoring it. It is about 80% done. Matt and I gave a talk this Summer for the Workshop at the Hartness House for the Antique Telescope Society on the progress so far in the restortation. Here is a link to a couple of pictures of the workshop http://www.flickr.co...in/photostream/

- Dave

#40 philipdo

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Posted 14 November 2012 - 12:58 PM

I'm impressed Dave. What a project !

#41 highfnum

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Posted 15 November 2012 - 07:48 PM

is it true a spectrohelioscope can get down to .2A and even .1A resolution?

#42 DAVIDG

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Posted 16 November 2012 - 09:05 AM

is it true a spectrohelioscope can get down to .2A and even .1A resolution?

Yes, it is a true spectrohelioscope and it is the exact same designed as published in Hale's article in ATM-1. It was commerically made by Howell and Sherburne. Here is a link to their sales booklet http://authors.libra...ohelioscope.pdf
I'm replacing the original 600 lines/inch grating with modern 1200 lpi one blazed at 550nm to improve the resolution. It's missing the Anderson prism assembly which I'm in the process of reproducing. I have the replacement prisms themselves.

- Dave

#43 highfnum

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Posted 16 November 2012 - 09:30 AM

link came up dead
i gotta get up to stellafane to see this thing once its working

#44 highfnum

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Posted 16 November 2012 - 09:37 AM

I built a 2400 line per mm spectroscope
a while back
took this shot

http://www.cloudynig...php?photo=17725

1) will 2400lines per mm work for such a device
2) why are some lines "thicker" then others - H-a line is thicker than H-b line

#45 DAVIDG

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Posted 16 November 2012 - 09:44 AM

link came up dead
i gotta get up to stellafane to see this thing once its working


Try the link again, it just worked for me. The server might have been down.

- Dave

#46 DAVIDG

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Posted 16 November 2012 - 09:57 AM

I built a 2400 line per mm spectroscope
a while back
took this shot

http://www.cloudynig...php?photo=17725

1) will 2400lines per mm work for such a device
2) why are some lines "thicker" then others - H-a line is thicker than H-b line


Yes a 2400 lines per mm grating will work well. The width of the lines is a function of the electron transistion in the atoms and also the Heisenburg Uncertainty Principle.

- Dave

#47 highfnum

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Posted 16 November 2012 - 02:12 PM

do you guys know about Fredrick Veio work with spectrhelioscope's?

#48 DAVIDG

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Posted 16 November 2012 - 02:58 PM

do you guys know about Fredrick Veio work with spectrohelioscope's?


Yes, very much so, there are references from me posted on his site and on the Yahoo spectrohelioscope group.

- Dave






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