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Calcium K filters

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#1 cardanoc

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Posted 28 September 2021 - 02:37 PM

Hi,

 

I've been doing H-alpha for several years and love it.

 

Ca K looks very interesting.

 

Has anyone had success or a bad experience with the Baader Ca K filter?

 

I would use it with the Lunt Herschel wedge.

 

Thanks for reading this.



#2 MalVeauX

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Posted 28 September 2021 - 03:05 PM

Hi,

 

The Baader K line filter is just a photosphere filter. It's not the lower cooler chromosphere of Calcium K because its simply too wide of a filter.

 

Also, near UV wavelengths are mostly not even visual because we cannot see much due to yellowing of our cornea over time. If you're purely visual, you may want to look to the Calcium H line such as a Quark Calcium.

 

Otherwise, the Lunt Calcium K module is 2.4A and narrow enough to show the chromosphere in calcium, if you can see that wavelength visually (it will be fine with a camera of course).

 

Very best,



#3 TOMDEY

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Posted 28 September 2021 - 03:30 PM

I got the Lunt ~straight through~ CaK filter years ago and it performs well spectrally... except that it has quite objectionable astigmatism, which is a disappointment. I actually bought that version because I figured it would be less apt to have a crummy wavefront. I never bothered to return it, so always wind up focusing to a "compromise" focus. So, occasionally, junk filters get through the Lunt production. And when Meade bought them out... junkiness became more of their mission and vision, rather than just occasional slip-ups. Hopefully, new owner Orion will straighten out Meade's/Lunt's quality issues.    Tom



#4 MalVeauX

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Posted 28 September 2021 - 03:38 PM

I got the Lunt ~straight through~ CaK filter years ago and it performs well spectrally... except that it has quite objectionable astigmatism, which is a disappointment. I actually bought that version because I figured it would be less apt to have a crummy wavefront. I never bothered to return it, so always wind up focusing to a "compromise" focus. So, occasionally, junk filters get through the Lunt production. And when Meade bought them out... junkiness became more of their mission and vision, rather than just occasional slip-ups. Hopefully, new owner Orion will straighten out Meade's/Lunt's quality issues.    Tom

Meade bought Coronado. Not Lunt. Orion bought Meade recently of course. But again, not Lunt.

 

Coronado had the PST CaK and an early CaK scope. These were excellent mostly. They're unicorns now.

 

Lunt's CaK modules are excellent.

 

Very best,


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#5 hopskipson

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Posted 28 September 2021 - 03:41 PM

I got the Lunt ~straight through~ CaK filter years ago and it performs well spectrally... except that it has quite objectionable astigmatism, which is a disappointment. I actually bought that version because I figured it would be less apt to have a crummy wavefront. I never bothered to return it, so always wind up focusing to a "compromise" focus. So, occasionally, junk filters get through the Lunt production. And when Meade bought them out... junkiness became more of their mission and vision, rather than just occasional slip-ups. Hopefully, new owner Orion will straighten out Meade's/Lunt's quality issues. Tom


I’m guessing when you’re saying Lunt you mean Coronado perhaps?? Lunt is a US company that is privately owned and Coronado is Meade’s solar product line. If you have a Coronado Calcium filter that you are not happy with I might be interested in it 😉

#6 hopskipson

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Posted 28 September 2021 - 03:41 PM

I got the Lunt ~straight through~ CaK filter years ago and it performs well spectrally... except that it has quite objectionable astigmatism, which is a disappointment. I actually bought that version because I figured it would be less apt to have a crummy wavefront. I never bothered to return it, so always wind up focusing to a "compromise" focus. So, occasionally, junk filters get through the Lunt production. And when Meade bought them out... junkiness became more of their mission and vision, rather than just occasional slip-ups. Hopefully, new owner Orion will straighten out Meade's/Lunt's quality issues. Tom


I’m guessing when you’re saying Lunt you mean Coronado perhaps?? Lunt is a US company that is privately owned and Coronado is Meade’s solar product line. If you have a Coronado Calcium filter that you are not happy with I might be interested in it 😉

#7 slavicek

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Posted 28 September 2021 - 03:46 PM

I bought the Lunt Ca K filter (diagonal version for observing), 3-4 years ago. I use it with binoviewer, and it works very well. When the Sun was quiet Ca K was more interesting then Ha (in my opinion). I also bought the Baader Ca K to use it as a "double stack" but that did not work. Baader filter is not for observing.



#8 Great Attractor

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Posted 28 September 2021 - 03:55 PM

I got the Lunt ~straight through~ CaK filter years ago and it performs well spectrally... except that it has quite objectionable astigmatism, which is a disappointment.

Try rotating the CaK module in 45° increments (keeping the telescope and camera+Barlow in place). My B600 shows terrible astigmatism in some orientations, I haven't yet figured out why, but rotating helps.


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#9 TOMDEY

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Posted 28 September 2021 - 05:07 PM

Meade bought Coronado. Not Lunt. Orion bought Meade recently of course. But again, not Lunt.

Coronado had the PST CaK and an early CaK scope. These were excellent mostly. They're unicorns now.

Lunt's CaK modules are excellent.

Very best,

Yikes! --- Thanx for the clarification. My Lunt CaK straight-thru has crummy/defective wavefront but excellent spectral characteristics. Funny that they would nail the tough part and screw up the easy part. I guess... because of that... I naturally assumed Meade had something to do with it. Nother part of the history is that Lunt was an offshoot of Coronado guys jumping ship? I may not know what I'm talking about, but express it with such passion. Somebody acquired Lunt... somebody responsible...  ? Tom (Loose Cannon Tom)


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#10 TOMDEY

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Posted 28 September 2021 - 05:09 PM

I’m guessing when you’re saying Lunt you mean Coronado perhaps?? Lunt is a US company that is privately owned and Coronado is Meade’s solar product line. If you have a Coronado Calcium filter that you are not happy with I might be interested in it

Good point! If I had a Coronado... I'd cherish it --- if not --- I'd be looking for one!    Tom



#11 TOMDEY

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Posted 28 September 2021 - 05:11 PM

Try rotating the CaK module in 45° increments (keeping the telescope and camera+Barlow in place). My B600 shows terrible astigmatism in some orientations, I haven't yet figured out why, but rotating helps.

Excellent point --- I'll try that --- cancelling astigmatisms no doubt. Maybe mine is similarly squirrely.    Tom



#12 MalVeauX

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Posted 28 September 2021 - 05:13 PM

Nother part of the history is that Lunt was an offshoot of Coronado guys jumping ship? I may not know what I'm talking about, but express it with such passion. Somebody acquired Lunt... somebody responsible...  ? Tom (Loose Cannon Tom)

I think the basic story goes: David Lunt is the original Lunt with the designs that became Coronado solar filters. That was the 90's. And then was sold, after David died (cancer) to Meade in 2004. It went to dookieville after that with the subsequent Coronado series filters getting worse and worse.

 

His son Andrew then founded Lunt solar systems and is still there and that team is doing a very good job with producing some of the better commercially available etalons.

 

Very best,



#13 cardanoc

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Posted 28 September 2021 - 05:35 PM

Are there any other filters out there beside Lunt and Baader?

 

Lunt is nice, but pricey.



#14 TOMDEY

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Posted 28 September 2021 - 05:36 PM

I think the basic story goes: David Lunt is the original Lunt with the designs that became Coronado solar filters. That was the 90's. And then was sold, after David died (cancer) to Meade in 2004. It went to dookieville after that with the subsequent Coronado series filters getting worse and worse.

 

His son Andrew then founded Lunt solar systems and is still there and that team is doing a very good job with producing some of the better commercially available etalons.

 

Very best,

Thanx... I'd better start rotating components and convince myself that the astig is in the Lunt CaK and not something else... and then apologize if the CaK is exonerated.

 

Anecdote: Years ago one of our techs was deftly wavefront inspecting fused silica beamsplitting prism substrates for interferometer builds... the tech specs appropriately and understandably extremely stringent... I looked over his shoulder and got him to splain what he was doing. I then gratuitously commented, "Whoever came up with that procedure must be a complete idiot!" A couple hours later Greg showed me the white-paper that led to the procedure. I'm looking it over and begin to realize that the originator was not only unidiotic... but profoundly insightful, even genius. The format and flawless logic seemed déjà vuish. Greg then pointed out the author --- he was me, about a decade earlier. Suddenly everything made sense. I apologized for criticizing the author, and composed a letter of commendation to his boss, saying he deserved a promotion. That came to pass. My next invention will have to be a Time Machine... seeing that I've already got a head start on its use.    Tom



#15 MalVeauX

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Posted 28 September 2021 - 05:41 PM

Are there any other filters out there beside Lunt and Baader?

 

Lunt is nice, but pricey.

There's no such thing as an inexpensive narrowband filter that shows the chromosphere in solar. The Daystar ones are 5~6A bandpass. The Lunt is 2.4A bandpass. Custom stuff goes down to 1A. It's basically $750~1300 minimum entry point for Calcium K/H. Anything 80A or wider bandpass will simply show the photosphere.

Very best,



#16 cardanoc

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Posted 28 September 2021 - 05:54 PM

Are any of the filter manufacturers (i.e., alluxa, omega..). Making Ca K filters?



#17 MalVeauX

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Posted 28 September 2021 - 06:26 PM

Are any of the filter manufacturers (i.e., alluxa, omega..). Making Ca K filters?

Chroma, Alluxa, etc, yes can make a custom CaK filter. It will cost more than a Lunt CaK module.

 

Very best,



#18 BYoesle

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Posted 29 September 2021 - 10:31 AM

Some history:

 

To the best of my knowledge Coronado started in Great Britain on the Isle of Man by David Lunt and his wife Gerry Hogan in 1997. David was the chief optical designer at the helm, and Coronado made many innovations to produce etalons specifically for solar filter use, which were later patented by Coronado with David’s son Andrew (Andy) Lunt and Yakov Sidorin – both talented optical designers in their own right.

 

When Coronado left the Isle of Man to relocate to Tucson, Ken Huggett (Andy Lunt’s uncle) remained behind and later started Solarscope filters in 2002. Since Coronado had the patented central spacer to maintain etalon plate uniformity and gap spacing temperature stability, the Solar Scope filters used the traditional thicker etalon plates and had no central obstruction. Coronado also patented the use of mechanical pressure tuning of air-spaced etalons – later generally referred to as “RichView” tuning by MEADE.

 

In the early 2000’s David became ill with prostate cancer, and Coronado began experience problems meeting demand. When David passed in 2005, Coronado had been sold to MEADE for capitalization.  After a short period of time, MEADE "released" the Tucson Coronado personnel, and moved all the etalon fabrication equipment and production first to Irvine, California, and then to Tijuana, Mexico.

 

Andy Lunt worked in optical design and fabrication for the aerospace industries and brought some of that technology to H-alpha solar telescopes. After a 1 year "no-compete" clause expired, Andy and some of the previous Coronado principles and employees who remained in Tucson then went on to form Lunt Solar Systems. Since all the patents developed by Coronado went to MEADE, Lunt Solar developed the “root3” spacer system for large etalons, and reverted to thicker etalon plates for the smaller unobstructed filter systems. Emphasis also shifted to internal collimator based etalon systems, versus the larger front-mounted etalon systems that Coronado originally produced. This also allows for the preferred method of etalon tuning via uniform air pressure changes versus tilt or mechanical compression tuning.

 

More information about David Lunt can be found here.


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