Baader Halpha Coronagraph (prominence viewer)

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Baader Halpha Coronagraph (prominence viewer)

Post by Montana » Mon Feb 13, 2017 7:23 pm

At the weekend I was kindly gifted a Coronagraph. I have done lots of reading on the web today and thought, easy, let's fit it together tonight. Dear oh dear, it has blown my little mind. Can anyone fathom out how I put this together, this is the only configuration I found that screws together.
Coronagraph small.jpg
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So my questions are

1. The cones are for a 1000mm focal length, my TEC140 is 980mm, will this not work? I will be stopping it down a little by adding my D-ERF which is 135mm (maybe 125mm) at the front. Does this alter things?

2. How do a screw a grasshopper in?

Here is the instructions if anyone can work out what on earth H1, V1, V2, H3 etc means in english :shock:

ImageBaader H alpha Coronagraph (prominence Viewer) by Alexandra Hart, on Flickr
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Kind regards
Alexandra

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by marktownley » Mon Feb 13, 2017 10:39 pm

Looks nice! It's all about spacings. It's whether the sun will stay out long enough to set it up :D
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Merlin66 » Tue Feb 14, 2017 4:00 am

Alexandra,
Let me review the documentation and get back to you, I'm sure we can figure it out....
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Merlin66 » Tue Feb 14, 2017 4:51 am

There's a good review of the Baader Prominence viewer in S&T, June 1994, p51.
It says it comes with different occulting disks (six off) to compensate for the changing solar diameter through out the year....
The illustration shows the occulting disk spacer at the front, a plain spacer, the spacer with the slot arrangement followed by a Baader marked spacer and the "eccentric viewer" attachment and finally the T thread to 1.25" adjustable adaptor......it also mentions a x2 teleconvertor in the kit.
To set it up on the sun, the author first fitted a Baader solar skreen filter, only removed when the solar disk was occulted....
Stay tuned.
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Merlin66 » Tue Feb 14, 2017 5:08 am

Alexandra,
As the parts are shown in your first image...
At the extreme lhs I think is a 2" nosepiece to fit the instrument into the scope focuser...
The assembly of the four chromed spacers looks correct. The first should have the "correct" occulting disk fitted...
The "Eccentric" is then fitted to the end of this train and then 1.25"/ T thread adaptor - this allows you to fit an eyepiece or your camera (to the T thread)

Not sure what the additional tubes are for (yet!) may be something to do with the optional x 2 teleconvertor???
Does this make any sense to you??
More to follow....
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Merlin66 » Tue Feb 14, 2017 5:16 am

OK, the H1, V1 etc are the numbers given to the individual spacer sections (and the eyepiece adaptor(s)
A detailed listing is shown on the top of page 6 of the manual.
Hope this helps.......
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Montana » Tue Feb 14, 2017 8:04 am

Oh I see, the black bit which does fit at the left hand side is the bit that goes into the focuser. It has threads on the end which are supposed to fit the Vixen telescope. I'll have to see whether it slides into my 2 inch focuser or not.

The silver extension tubes are what confuse me, I thought they would be on the left hand side but it is just a touch too large to screw on to the silver coronagraph part. In this photo it shows it before, but that is impossible as the threads just don't fit? (he has 5 silver segments - the coronagraph has 4 parts so he must be using one of the silver extension tubes somewhere). http://www.cloudynights.com/page/articl ... agraph-r36

Oh unless it fits on the other end before the excenter (whatever that is?) I'll try that tonight!

Alexandra

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by DavidG » Tue Feb 14, 2017 3:53 pm

Hi,
Having designed and built coronagraphs from scratch I'll be happy to try to happy. http://considine.net/dgroski/promscope/ The first issue you might have are the occulting cones. The diameter is determined by the size of the solar disk produced by the telescope. The Sun's disk is approximately 1% of the focal length of the telescope so in your case 9.8mm . The ones provided as you said for 1000mm fl so 10mm in diameter. They vary slightly in diameter because the Sun changes diameter through the year because of our orbit. So they are too big. So you'll need to use a variable barlow to increase the size of the solar disk to match the occulating disk size.
You want to assemble the unit so your able the to focus the eyepiece on the edge of occulting disk by moving the eyepiece. With the unit in the focuser you focus so the limb of the Sun is in sharp focus So now you have both the edge of the occulting disk and the limb of the Sun in sharp focus. Next you move the telescope so the Sun is exactly behind the occulting disk and you adjust the iris to maximize the contrast of the prominence vs the back ground sky.
The spacer tubes allow you add space before the occulting disk so you can bring the solar disk to focus on it and to add space after the narrow band filter at the end of the unit so you can focus an eyepiece on the edge of the occulting disk.

- Dave
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Montana » Tue Feb 14, 2017 7:38 pm

Fantastic Dave! you are a star.
OK more questions, I can't seem to fit the extension tubes on either end of the prominence viewer part? I don't understand why they would be in the box if they don't quite fit, it is fractional. Or am I not being patient enough, however the hubby tried and he thought they were too big on one side and too small on the other end ;)

Variable barlow, I see what you mean, I don't have one. Would you put that before the occulting disc or after? just so I know what size barlow I would need 2", 1.25" or 1.75" as this beast is.

I have just found I need a 2" to 1.75" adaptor to fit it in the focuser.
So that looks like 2 items for the shopping list so far.

Do you know what the excenter is/does?

Many many thanks
Alexandra

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Merlin66 » Tue Feb 14, 2017 9:00 pm

Alexandra,
The excentre provides the necessary off set from the optical axis to position the eyepiece/camera at the edge of the solar disk.
(The occulting disk must be positioned exactly over the solar disk, so there no opportunity to move the scope etc to bring the edge into the FOV.)
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
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"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by DavidG » Tue Feb 14, 2017 10:51 pm

The main parts should be the tube with the lens and occulting disk, with the occulting disk facing the focuser of the telescope. Next, what screws on the back of that tube ( end without the lens/disk) is the tube with the iris, and screwed on to that is the tube with the second lens without the disk. On to to this last tube screws in the ring that contains the narrow band filter. On to that ring you would attach one or more of the extension tubes. On to the extension tube(s) you attached the adapter for the eyepiece. So be sure you have these parts attached to each other correctly
If you use the eccentric unit it screws on to last extension tube then eyepiece adapter screw on to it. Why you might need this part , is when your using a low power eyepiece you'll see the occulting is disk in the middle of the field of view. With the Sun behind the disk you'll see the prtominence around the rim of the occulting disk. So if you want to increase the magnification to view a prominence in more detail, the occult disk get bigger but it is still in the middle of the field of view. You can 't move the edge of the disk into the middle of the eyepiece ! So what the eccentric adapter allows you to do is move the eyepiece off center so now the edge of the disk with the prom sticking out is in the middle of the higher power eyepiece.
With your telescope having a focal length of 980 and the occulting cones made for 1000ml fl, you would need a barlow that only magnifies 1.02x ( 1000/980 = 1.02) That is a very small amount but if the Sun's image doesn't match that of the cones very closely either the proms can be hidden behind edge of the disk or if the cone is too small too much light will get in and they will be washed out. So try using the smallest diameter cone you have and see how that works. If it doesn't work OK you might have to use a scope with 1000mm fl, or one with 500mm and 2x barlow or have a custom set of cones made.
I machined one cone and a set of washers that go behind the cone of different diameters for my setup.

- Dave
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Montana » Wed Feb 15, 2017 8:04 am

Mmmm lots to think about!

Mine seems to be in a slightly different order to what you said. It was already put together but do you think it was put together in the wrong order and I need to shuffle part 'unknown' and the 'iris' the other way round?
Coronagraph.jpg
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Alexandra

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Merlin66 » Wed Feb 15, 2017 8:27 am

No,
That seems to be the way it is shown in the 1994 review.
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https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Montana » Wed Feb 15, 2017 8:31 am

I think 'unknown' is V2 in the instructions, it is just an extension tube and it seems to be in the right place. So it is in the right order after all :)
Coronagraph a.jpg
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I think I will contact Baader and see what they say about the cones :(

Alexandra

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by DavidG » Wed Feb 15, 2017 3:16 pm

The key is that H2 that contains the Iris is located at the aperture stop of the system So V2 might not be in the correct position. Here is a link to my math that shows how to calculate the spacing for all the elements in a solar coronagraph. http://considine.net/dgroski/promscope/prom3.gif so you can get a good idea of the focal length of the lens in H1 by just using it with the Sun. Then use that values to calculate were the Iris should be.
I also think the filter should not be at the end of H3 but at the end of H2 and and the tube with the Baader writing on it should screw into the filter then the eyepiece adapter. You need to have enough spaces after the filter so that when the Iris is fully open you can focus the eyepiece on the edge of the occulting cone. The operation is same as the cross hairs in a finderscope. The optics in the eyepiece are adjusted so the cross hairs are in sharp focus, then the eyepiece is adjusted so the image is also in sharp focus. It's the same for the coronagraph with the edge of the occulting disk and the image of the Sun both need to be in sharp focus at the same time. That is the purpose of the extension tubes that go before after the main optics of the coronagraph. They allow the unit to have the Sun focused the occulting cone and bring the eyepiece to be focus on the occulting cone at the same time for different eyepieces and different amount focuser travel for different brands of telescopes.

- Dave
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Montana » Thu Feb 16, 2017 12:18 pm

Thanks guys, well I guess the only way to see whether the cones fit is to try them. I have now ordered an adapter to screw on V1 with a 2" end so it will fit in the focuser, I guess that is a good start :)

Alexandra

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by DavidG » Thu Feb 16, 2017 3:21 pm

You can assembly the unit minus the narrow band filter and see if you can get an eyepiece to focus of the edge of the cone. Since the Moon is about the same diameter as the Sun you can try the unit out again without the narrow band filter in place to see if you can get the Moon and the occulting cone at focus and the same time and what extension tubes you might need to do this.

- Dave
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Montana » Sat Feb 18, 2017 9:27 am

Still waiting for the adaptor to attach it to the scope but I have found out a little more history of this instrument. It was owned by the late HPJ Douglas Arnold who died in 2006. He took this image with it using a colour film camera, quite impressive I think
Image

I hope I manage to get something as good :)

Alexandra

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Carbon60 » Sat Feb 18, 2017 6:50 pm

Looking forward to seeing some results, Alexandra......assuming we'll see the Sun again sometime soon.

Nice device.

Stu.
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Re: Baader Halpha Coronagraph (prominence viewer)

Post by DavidG » Wed Feb 22, 2017 4:34 pm

Have you checked the narrow band filter ? If your unit is 10 years old then the filter might have aged and is no longer on band.

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by Montana » Wed Feb 22, 2017 4:56 pm

Hello Dave, I have no other way of checking it other than using it, currently I am still waiting for the 2" to M43 adaptor and I haven't seen the Sun since Christmas :(
Here is a photo of it, it is dated 1993 so it is a little over 10 years old :)
ImageBaader H alpha Coronagraph (prominence Viewer) by Alexandra Hart, on Flickr

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Re: Baader Halpha Coronagraph (prominence viewer)

Post by DavidG » Wed Feb 22, 2017 9:18 pm

With it being 24 years old the odds are very good that it has drifted off the CWL of 656 and is also cloudy. It should look perfectly clear so if you see any hazy it has problems.

- Dave
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