Baader Coronagraph

Use this section to discuss "standard" Baader/Coronado/ Lunt SolarView/ Daystar, etc… filters, cameras and scopes. No mods, just questions/ answers and reviews.
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george9
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Baader Coronagraph

Post by george9 » Sat Jul 04, 2020 3:05 pm

I acquired a Baader Coronagraph for fun, plus a matching Celestron (Vixen) 80mm refractor. The H-alpha filter is deteriorating, and the price reflected that.

Normally when a filter deteriorates it gets darker, not lighter, so it is probably safe. But I was thinking of putting a Beloptic UV-IR KG3 cut filter in the train just to be sure (I already know the visible light is not too bright).

I noticed the color of the Sun was pink instead of red, and my hand spectrograph shows spikes at both H-alpha and somewhere in green. Maybe magnesium? Is that what the original Baader filters did, or is this just a deterioration?

Alexandra, I know you replaced your filter, but was yours pink before you replaced it? Alex, yours may be original.

I was thinking of using my Prom15T 2A H-alpha prom filter, but I would have to duplicate the ERF to make it safe. I am guessing I need RG630 and KG3, but I really don't want to guess. For imaging it would be fine, but I am conservative on visual. I do have an Edmunds 3mm thick 1" RG630 and a 2" Beloptic KG3 (Oliver is out of 1.25" right now).

(By the way be careful. This group is savvy but it would be easy to take something like a Baader Red 610nm longpass filter thinking it will work similar to an RG610 or RG630 and not realize that it transmits a blinding amount of green light. Also Wratten 25.)

George



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Re: Baader Coronagraph

Post by Montana » Sat Jul 04, 2020 5:35 pm

George, I have never used mine for visual, I was too nervous to do this as it was so old. I have always used a Baader D-ERF on the front of the objective and I sent mine back to Wolfgang Lille who fixed it as it was deteriorated. I can't remember exactly what he added but he also added red filters as well in the mix. I would have to check when I get back home as I can't remember.

Always be on the cautious side with your eyes with these old relics! Mine is lovely now it is refurbished but it did cost €1000 to fix ;)

Alexandra



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Re: Baader Coronagraph

Post by george9 » Sun Jul 05, 2020 1:17 am

Thanks, Alexandra. I agree. My general rule is I don't view unless I have a complete commercial visual filter in series with whatever I come up with.

The Prom15T will be for imaging only and sounds like so will be the original H-alpha filter. I guess I could try to find a commercial 2A prom filter to use with the coronagraph, but no need to spend the money.

(Similarly, I always use Baader visual film to view continuum on my C11 because I know that is safe. I could rig up something with my Aries filter but I don't quite trust my not making some mistake. For imaging continuum, then definitely the Aries.)

George



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Re: Baader Coronagraph

Post by george9 » Sun Jul 05, 2020 3:57 am

Or maybe that extra green band is 530nm for FeXIV in the hope to get that bright but low coronal emission over an active region (I just learned about it, so I may have it wrong)? I measured 540nm in my hand spectroscope, but it is not very accurate.

George



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Re: Baader Coronagraph

Post by george9 » Sun Jul 05, 2020 9:15 pm

For the record, nope, not 530. More like 547nm. I looked at a reflection of the Sun off the floor in the spectroscope and logged the bands, and 530 was lower than the coronagraph line. I cannot find anything of interest at 547, so I suspect it is a degraded filter. A very narrow line though.

George



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Re: Baader Coronagraph

Post by mdwmark » Tue Jul 07, 2020 6:19 am

That sounds like your talking about only the bandpass part of the filter.
If you make an bandpass at Ha , it will turn back on in the green, and be full on in the blue end of the spectrum. On the long side it will start back on around 780nm.
The bandpass normally used were 5 Ang two cavity and blocked to the far IR.
You might PM me what you got and I could check what you need.
Mark W.



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Re: Baader Coronagraph

Post by george9 » Thu Jul 23, 2020 1:59 am

Thanks, Mark. I had missed this. That's actually the whole filter assembly. I suspect the degradation has let some green through. I have not yet actually proven that the red line is still in H-alpha, but that should be easier to check. I may just try to use my Prom15T, adding an RG630 and KG3, using it for imaging only.

George



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Re: Baader Coronagraph

Post by george9 » Thu Jul 23, 2020 2:12 am

Alexandra or others with experience, I am having trouble focusing the cone on the camera. It seems that the mount on the lens that the cone is attached to is larger than the cones themselves, so I am not sure I can get around it to see the cone.

That is, there are a series of cones that screw onto a shaft that slides back and forth to help with focus. That shaft is mounted on a lens. In my case, the mount on the lens is pretty wide, a little bigger than the cones themselves. Is it supposed to be that way, or perhaps the mounting was damaged and someone repaired it?

I am trying to push the cone forward away from the lens and seeing if I can focus in that case.

If I pull the camera back, I can purposely focus on the mounting on the lens (i.e., behind the cone). Then I get a pretty irregular circle because the mounting is not perfect like the cones. As I push forward I am not sure if I get to the cone, or it is just an out-of-focus mounting.

I also tried using the largest cone (longest focal length in January), but it did not seem to help.

George



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Re: Baader Coronagraph

Post by Montana » Thu Jul 23, 2020 7:28 am

George have you read my blog notes? https://solarnutcase.livejournal.com/18374.html

Getting focus in all the right places is all about distances between all the appropriate parts. It took me many hours and help from Wolfgang to get them all correct.

Make sure you do not over tighten the cone, it must be left slightly loose I think due to heat expansion and never touch the cones either without the gloves on. The cone screws on, I am not quite clear on what you mean by push? We really could do with photos and comparing them to mine.

Alexandra



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Re: Baader Coronagraph

Post by george9 » Thu Jul 23, 2020 2:50 pm

Thanks, Alexandra. I did look at the blog. I cannot tell from your photo, but here is mine. There is the silver cone at top. It sits on a stalk. The cone actually moves into and out of the lens, as described in my copy of the Baader manual. (And if you pull the cone too far out, you start to see a red warning ring on the stalk, just as described in the manual.) At the base of the stalk you see a black disk, which is part of the mounting onto the lens. It is hard to tell from this perspective, but that disk is wider than the base of the cone, and that cone is the widest in my set. So I can focus on that black disk very easily, but harder to wrap around and focus on the base of the silver cone. I would have thought that the mounting disk would be hidden by the cone. There is the lens there, so it is possible that the way it works is that I do get partial illumination of the edge of the cone, with light refracted back towards the center. And maybe that is on purpose to eliminate some kind of stray light. But I just was not expecting it.

George
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Re: Baader Coronagraph

Post by Montana » Thu Jul 23, 2020 3:05 pm

That's weird, I need to go and look at mine and the manual

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Re: Baader Coronagraph

Post by Montana » Thu Jul 23, 2020 5:56 pm

I've had a look George and yes you are right, in the instructions it says you can pull it out but don't leave it there otherwise it ruins the collimation of the cone. I have never seen it out and it has always been flush with the glass, I thought that it meant that you didn't have to screw it all the way down, not that you could pull it out. I would rather not try as mine is working well and I don't like to fiddle (currently everything in my house is broken at the moment and I don't want to add it to the list).

Here is a pic of mine, it is flush with the glass

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

Alexandra



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Re: Baader Coronagraph

Post by Montana » Thu Jul 23, 2020 6:06 pm

I've taken another picture
DSC09100s.jpg
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Alexandra



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Re: Baader Coronagraph

Post by george9 » Thu Jul 23, 2020 7:24 pm

Thanks for the photos. No need to pull it out. The important thing is that I don't see a big black disk behind it.

Mine looks like an integral part of the system, so I don't think someone just stuck it there. It is what the stalk is attached to. I'll do some more testing. Maybe measure it with a caliper to get the exact sizes.

George



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Re: Baader Coronagraph

Post by george9 » Fri Jul 24, 2020 2:51 am

Some more information:

The black disk on the lens that is shown in my photo is 9.4mm. The cones that came with my set range from 8.4mm for 910mm f.l. in July to 8.8mm for 910mm in January to 9.9mm for 1040mm f.l. in January. If the cone is over 9.4mm, then you are set.

For smaller cones, there are two ways to look at it. One is just look at the 8.4mm cone from the other side of the lens. Normally you wouldn't see it, hidden behind the 9.4mm disk. But the disk sits on a magnifier, which--if the cone is far enough away--enlarges the apparent size of the cone so that you effectively see it around the larger disk. The other way to look at it is to draw the rays coming from each side of the Sun, through the objective, to the disk. But then the light never gets around the disk.

The other possibility is that the lens mount was designed for the 1040mm f.l. scope and the owner added the 910mm set without realizing that they needed a slightly different lens mount. It means I might need a slight Barlow to extend the effective focal length to 1040mm. I notice that the 1040mm cone set fits in the carrying case, but the 910mm and 1000mm sets do not fit in the case. So it may indeed have been designed for 1040mm.

George



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Re: Baader Coronagraph

Post by Montana » Fri Jul 24, 2020 7:14 am

That could be correct! mine is for the 1000mm focal length and the cones are definitely wider than any of the mounting components.

Alexandra



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Re: Baader Coronagraph

Post by george9 » Sat Aug 01, 2020 2:44 am

Here are a few first-light shots through the coronagraph on an 80mm. My imaging skills are limited, and these are single, raw images. Zero processing.

I could work on focus, narrowing the iris, etc. And I was looking through very thin clouds. But given the tiny proms, this was pretty good.
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The Prom15T actually gave a mottled image with some detail on the active region when I shot the solar disk with the Sun off the cone. I am afraid that I failed to image it.

For comparison, here are some single images through my 6" with RG32. The view was great and the proms were detailed visually, believe it or not. So this is mostly my lack of imaging ability. Those are the same proms as in the coronagraph.
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George



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Re: Baader Coronagraph

Post by Montana » Sat Aug 01, 2020 9:24 am

Wow!! well done! I found imaging through the coronograph very hard indeed, it is great for sketching though :) Looks like it is all working then :hamster:

:bow
Alexandra



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Re: Baader Coronagraph

Post by george9 » Sat Aug 01, 2020 1:36 pm

Thanks. I ended up using the smaller cone from the 1040mm series. It's like being at a 7-minute eclipse instead of a 30-second eclipse. My camera has a narrow field, so I can always inch that limb to the edge.

George



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