Lunt calcium filter imaging thread

[Montana]

This is my best
220516_081515 by Alexandra Hart, on Flickr

But mostly like this
180617_073020 by Alexandra Hart, on Flickr

These are the best, 99% I through away as they are blurred after processing.

Alexandra

[Valery]

Apollo,

Lunt CaK is 2,4A and the PST is 2.2A. I have compared the Lunt CaK 12mm diagonal and my PST CaK in the configuration I have now.
Lunt was better than PST CaK if the PST CaK was single stacked. I belive this was because the blocking filter of the PST was rusty. I stick with the PST hoping to change the bloking filter for baader K-line. This was not realized yet.

As far as I know, the PST CaK is 3 or 4 cavity filter. It works very good from F/7 to F/40 without noticeable degradation at F/7.
Same with the Lunt CaK filter.

[christian viladrich]

Here is an image taken a while ago with the Lunt Ca K filter:


This is quite a good Ca K filter. I use it with a 150 mm refractor and no ERF with no problem. But don't use it with a larger aperture and no ERF. A friend tested it with a 200 mm and the fiter got damaged ...

[Valery]

Here is an image taken a while ago with the Lunt Ca K filter:


This is quite a good Ca K filter. I use it with a 150 mm refractor and no ERF with no problem. But don't use it with a larger aperture and no ERF. A friend tested it with a 200 mm and the fiter got damaged ...

Christian,

Thanks for the input.

BTW Did you ever perform the direct comparision of your Barr CaK and Lunt CaK filters?


Valery

[marktownley]

Spherical aberration is the key hindrance at these wavelengths.

[christian viladrich]

I also found out that old one taken with the Lunt CaK :


Valery, you made me check my data log :-)
In fact, I broke my Baader K-line filter (which I used at that time as an ERF for the Barr Ca K filter) when I had the Lunt Ca K for testing. So I have no direct comparison.

This being said, the difference between the Baar filter and the Lunt is clear when you compare the image I took with the Lunt on August 17 (in my previous message above) and the image taken one day earlier with the Barr filter :


Another point of interest is that the images with the Lunt and the Barr filters are taken with the some exposure time, while the image scale of the image with the Baar is much larger. This means that the transmission of the Barr filter is higher that the transmission of the Lunt.

[p_zetner]

Here are older images taken of the full disk, an AR closeup and proms (with inverted disk). All were taken with Lunt B1800. All except the full disk had the Lunt stacked with an Omega 2 Angstrom (nominally) filter. Possibly a contrast improvement ... not sure and didn't really carry out study with / without the Omega.

Cheers.
Peter

full disk labels siz.png (2.27 MiB) Viewed 1111 times

AR closeup labels siz.png (2.95 MiB) Viewed 1111 times

prom inv disk labels siz.png (2.41 MiB) Viewed 1111 times

[christian viladrich]

BTW, in adddition to the Lunt, the Daystar Ca H filter is another good Ca K filter.

[marktownley]

Peter has got an apo-triplet. that explains it! Super-apo telescopes are just in a league of their own for all wavelengths. I cant beat that high strehl ratio with out using my 150mm f15....

At 393 it's not about strehl it's about spherical aberration. That 115/7 (along with the TOAs) have very little SA down in the blue. High strehl is definitely not a indicator a scope will perform well deep down in the blue.

[christian viladrich]

Hello Mark,
If I may, I would suggest rephrasing your statement as follows :
"the Strelh ratio at 436 nm (g band for the opticians) is not relevant to the performance of the refractor at 393 nm".
This is because the spherical aberration increases very fast when you go to shorter wavelengths.

Here is an example with the SC :

Because of the refractive index evolution with the wavelength, spherical aberration increases gently with longer wavelengths, and sharply will shorter wavelengthx.

Indeed, the Strehl ratio includes all aberrations of the optics. Accordingly, The Strelh ratio at 393 nm is fully relevant to the performance of the optic at 393 nm. The optics is diffraction limited when the Strelh is greater than 0.8.

Best regards

[Valery]

This image is at 393nm continuum taken with a standard C11 280mm F/10 telescope.

download/file.php?id=34233

The image is quite crisp.

[marktownley]

Hello Mark,
If I may, I would suggest rephrasing your statement as follows :
"the Strelh ratio at 436 nm (g band for the opticians) is not relevant to the performance of the refractor at 393 nm".
This is because the spherical aberration increases very fast when you go to shorter wavelengths.

Here is an example with the SC :

Because of the refractive index evolution with the wavelength, spherical aberration increases gently with longer wavelengths, and sharply will shorter wavelengthx.

Indeed, the Strehl ratio includes all aberrations of the optics. Accordingly, The Strelh ratio at 393 nm is fully relevant to the performance of the optic at 393 nm. The optics is diffraction limited when the Strelh is greater than 0.8.

Best regards

Fair point Christian, that says it better than I put it.

[marktownley]

This image is at 393nm continuum taken with a standard C11 280mm F/10 telescope.

download/file.php?id=34233

The image is quite crisp.

Hi Valery,

Is the c11 one that you selected from a number over time, or this the only one you've had?

Mark

[Valery]

This image is at 393nm continuum taken with a standard C11 280mm F/10 telescope.

download/file.php?id=34233

The image is quite crisp.

Hi Valery,

Is the c11 one that you selected from a number over time, or this the only one you've had?

Mark

This is the very same C11 telescope I started the high res imaging with. It has very average optics. I'd better have
a telescope with somewhat smoother optics.

[Valery]

This image is at 393nm continuum taken with a standard C11 280mm F/10 telescope.

download/file.php?id=34233

The image is quite crisp.

Valery: it is a good image, but it is not entirely "crisp". It is very blurry to my eyes, and it is over processed to bring out the details. Processing is a personal ability, and not a good indication of how well the scope is. It is a factor of lucky imaging.

You would get a better image if the optics were turned in favor of the blue wavelength, your hydrogen alpha image is the proof in the pudding. It is so much sharper, and has pure definition across all the whole-image. Which means the optics on the c11 are definitely made for h-alpha more than calcium. (as they should be, it is a deep space imaging scope)

If you could post the single frame data or a 10 frame raw data animation we can conclude the sharpness with better opinion of the sct optics. http://gifmaker.org/ (just extract 10 frames from the .avi file using avidub and upload them to gifmaker)

Post 10 frames of h-alpha raw, and 10 frames of calcium raw (unedited, unprocessed, screen grabbed straight from the .ser capture.)

Again, the image is great. But, there are definitely better optics out there for this color, like peters. We all work with what we have.


However I would trade the c11 for the apo triplet every day of the week,. (sacrificing the aperture for the strehl)

Valery: if i could give you my 150mm f/15 telescope, i would. You would likely use many times over the c11 and c14. Sometimes more aperture is not always the best choice, but of course; aperture IS king!


Christian your images are going to be very helpful! Thanks for posting.

This image is nearly as 1,6x larger scale than the H-a image, Apollo. Resolution corresponds to 11" aperture at this wave length. High is not possible. Corrective optics has been used. Remember for the future: Valery is optical designer and systems and optics maker in a past and I know something in optics...

[marktownley]

I thought this scope was a good example of how strehl varies with wavelength - the apm 152/7.8 doublet https://www.apm-telescopes.de/en/telesc ... 9-ota.html At either end of the spectrum the strehl plummets away

Strehlkurve.jpg (133.05 KiB) Viewed 902 times

[MapleRidge]

Hi All...

I pillaged the image archive on the weekend and pulled together a few examples of CaK images I've taken over the past 10 years. As requested, no pics of the hardware, but the evolution of the imaging systems used is listed below:

2008 - 2010 - Lunt 60mm/B1200CaK scope or a Williams Optic 72mm, f6/B1200CaK (the B1200CaK module was interchanged between the two OTA's
2010 - 2012 - Lunt B1200CaK + Celestron C102 OTA
2012 - 2016 - Lunt B1800CaK + IStar 150mm, f8 OTA or CR-150, f8 OTA
2016 - Present - Lunt B1800CaK/Solar Wedge Hybrid/Baader CaK filter + IStar 150mm, f8 OTA

Cameras used are primarily PGR Grasshopper Xpress (ICX674 chip), ZWO 175MM, and ZWO 1600mm.

The early years...2009-2013:

29 August 2010 with the C102

10cm-CaK-01B.jpg (72.81 KiB) Viewed 675 times

12 January 2011 with the C102

10cm-CaK-01.jpg (102.17 KiB) Viewed 675 times

23 October 2011 with the WO72

full_WO72_CaK-02.jpg (98.82 KiB) Viewed 675 times

16 November 2013 with the C102

24x_C102_CaK_172054.jpg (402.77 KiB) Viewed 675 times

16 November 2013 with the C102

24x_C102_CaK_172426.jpg (590.02 KiB) Viewed 675 times

16 November 2013 with the C102

24x_C102_CaK_172459.jpg (645.03 KiB) Viewed 675 times

2014-2018:

04 February 2014 with the CR-150

CR-150Prime_CaK_152855.jpg (1.74 MiB) Viewed 675 times

04 February 2014 with the CR-150

CR-150Prime_CaK_153458.jpg (1.2 MiB) Viewed 675 times

08 February 2014 with the WO72

Full_WO72_CaK_161555.jpg (123.3 KiB) Viewed 675 times

08 February 2014 with the iStar 150

IS_25x_CaK_154038.jpg (300 KiB) Viewed 675 times

15 February 2014 with the iStar 150

Prime_IS_CaK-DS_162139.jpg (958.2 KiB) Viewed 675 times

16 March 2014 with the iStar 150

CaK-proms.jpg (153.76 KiB) Viewed 675 times

11 February 2016 with the iStar 150

IS_124137_CaK-IS150-ASI.jpg (803.58 KiB) Viewed 675 times

11 February 2016 with the iStar 150

IS_124743_CaK-IS150-ASI.jpg (802.15 KiB) Viewed 675 times

14 April 2016 with the iStar 150

IS_133119_CaK-ASI.jpg (261.54 KiB) Viewed 675 times

25 August 2017 with the iStar 150

IS_CaK_104647-ASI.jpg (758.64 KiB) Viewed 675 times

The days of solar maximum certainly made a CaK filter a joy to use

If there are any questions just let me know.

Brian

[george9]

Nice. Makes me look forward to the next maximum, assuming we have one. George

[MapleRidge]

It is too bad that some places on earth suffer from the pollution as shown in the pic posted for the 'televised sunrise'. I suspect that unless there is major change in thinking these places will continue to degrade. I only hope that clearer minds will continue to push efforts to preserve the environment for generations that have not been born yet.

Brian