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Equipment Discussions >> ATM, Optics and DIY Forum

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DAVIDG
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Reged: 12/02/04

Loc: Hockessin, De
Re: question about H-alfa filter new [Re: highfnum]
      #5502245 - 11/03/12 11:31 AM

Quote:

Dave do you know where to get h-beta




John,
I haven't found a H-beta that would be narrower enough. All the 'DeepSky' type have a bandpass of 10nm (100A) or more but you might try looking for a filter designed for an Argon laser which is 488nm vs 486nm for the H-beta. When you tilt the filter it will shift toward shorter wavelengths and transmitt the H-beta wavelength. Here is a listing on Ebay from Omega optics for a narrow band 488nm filter with 1nm bandwidth. You'll need to be sure that it doesn't transmitt UV and IR or add addition filter to make safe but with coronagraph it might work.
Omega Filter

All the Best,
- Dave


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philipdo
sage


Reged: 12/06/06

Loc: Flanders, Belgium, Europe
Re: question about H-alfa filter new [Re: DAVIDG]
      #5502454 - 11/03/12 01:58 PM

Dave,

I like the idea with the barlow. I will post some pictures later on, when I get the new filter. It's an old homemade scope, made by Dany Cardoen of Puimichel, France. Probably from his early days in France, somewhere around 1983.


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philipdo
sage


Reged: 12/06/06

Loc: Flanders, Belgium, Europe
Re: question about H-alfa filter new [Re: philipdo]
      #5515924 - 11/12/12 12:33 PM Attachment (36 downloads)

Last week I received my Ha-filter 0,15 nm / 1,5 A from Omega Optical. Guess what, it has been rainy and overcast since. A few short sunny spells allowed me to quickly test the new filter. I liked what I saw: beautiful, contrasty prominences all around the solar limb, a beautiful arch... I was bothered however by some kind of internal reflection, probably due to the occulting cone that did not completely cover the sun's disc. With the appropriate cone, the reflection was gone. I've added some pictures of the coronagraph, hatch open, mounted to my Orion Atlas by means of a makeshift saddle.

Edited by philipdo (11/12/12 12:37 PM)


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philipdo
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Reged: 12/06/06

Loc: Flanders, Belgium, Europe
Re: question about H-alfa filter new [Re: philipdo]
      #5515934 - 11/12/12 12:38 PM Attachment (17 downloads)

close-up of the internals

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highfnum
Carpal Tunnel
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Reged: 09/06/06

Loc: NE USA
Re: question about H-alfa filter new [Re: philipdo]
      #5515951 - 11/12/12 12:44 PM

cool nioe work

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DAVIDG
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Loc: Hockessin, De
Re: question about H-alfa filter new [Re: highfnum]
      #5515979 - 11/12/12 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



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philipdo
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Reged: 12/06/06

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Re: question about H-alfa filter new [Re: highfnum]
      #5515980 - 11/12/12 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.


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philipdo
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Reged: 12/06/06

Loc: Flanders, Belgium, Europe
Re: question about H-alfa filter new [Re: DAVIDG]
      #5515987 - 11/12/12 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.


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nytecam
Postmaster


Reged: 08/20/05

Loc: London UK
Re: question about H-alfa filter new [Re: philipdo]
      #5517243 - 11/13/12 03:39 AM

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

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


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DAVIDG
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Re: question about H-alfa filter new [Re: nytecam]
      #5517518 - 11/13/12 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


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philipdo
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Reged: 12/06/06

Loc: Flanders, Belgium, Europe
Re: question about H-alfa filter new [Re: DAVIDG]
      #5517870 - 11/13/12 12:47 PM Attachment (12 downloads)

@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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DAVIDG
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Re: question about H-alfa filter new [Re: philipdo]
      #5517951 - 11/13/12 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


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philipdo
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Reged: 12/06/06

Loc: Flanders, Belgium, Europe
Re: question about H-alfa filter new [Re: DAVIDG]
      #5517988 - 11/13/12 01:48 PM

Dave,

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


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highfnum
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Reged: 09/06/06

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Re: question about H-alfa filter new [Re: philipdo]
      #5518181 - 11/13/12 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

Edited by highfnum (11/13/12 03:49 PM)


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philipdo
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Reged: 12/06/06

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Re: question about H-alfa filter new [Re: highfnum]
      #5518288 - 11/13/12 04:52 PM

Highfnum,

60K feet...Do you think the scope would qualify as airplane hand luggage ? 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.


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highfnum
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Re: question about H-alfa filter new [Re: philipdo]
      #5518511 - 11/13/12 06:55 PM

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

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philipdo
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Reged: 12/06/06

Loc: Flanders, Belgium, Europe
Re: question about H-alfa filter new [Re: highfnum]
      #5519263 - 11/14/12 09:46 AM

appr. 8 mm diameter and 10 mm FL

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DAVIDG
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Reged: 12/02/04

Loc: Hockessin, De
Re: question about H-alfa filter new [Re: philipdo]
      #5519302 - 11/14/12 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


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DAVIDG
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Loc: Hockessin, De
Re: question about H-alfa filter new [Re: philipdo]
      #5519322 - 11/14/12 10:38 AM

Quote:

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.com/watch?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.com/photos/30623046@N08/7828173638/in/photostream/

- Dave


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philipdo
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Reged: 12/06/06

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Re: question about H-alfa filter new [Re: DAVIDG]
      #5519507 - 11/14/12 12:58 PM

I'm impressed Dave. What a project !

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