May 20 CaK disc and H-alpha proms

[krakatoa1883]

The Sun shows today some fine details although that bright region close to the NE limb developed only two minor pores, at least for now. I started taking the usual CaK disc with the Lunt module

2020-05-20-0948-RB-Cak-fulldisc Lunt.jpg (79.31 KiB) Viewed 2146 times

then I removed the 2" blocking filter nose (very awkward) and replaced it with a Baader B-CCD (telescope side) and a K-line filter (sensor side)

2020-05-20-1142-RB-CaK-fulldisc Kline.jpg (67.17 KiB) Viewed 2146 times

The result is not bad at all and it's worth of further experiments. I am not satisfied with my Lunt Cak module, it causes ghost images and astigmatism and I have been able to obtain better images of the inverse granulation by using of the Quark Calcium in spite of its larger BP, probably because it better preserves the wavefront and doesn't have a tilted BF. So I will replace the Lunt BF with something different, still searching for the best option.

There were also few beautiful prominences, some quite bright even in calcium light. Thanks for looking.

[rsfoto]

Great close up images as well as CaK

[JochenM]

Very nice, Raf.

Love those CaK proms.

[Montana]

Wow!! those CaK proms are special
Alexandra

[krakatoa1883]

Thanks for your comments!

[LTHB]

Nice images, CaK as well as the AR in h-alpha! I've never succeeded to capture proms in CaK so far - yours are really bright and clear!

If you are still looking for CaK-filter options: My experience with the Baader blue CCD-filter is not that good, my copy has about 35% transmission in CaK. Much better for CaK purposes are the blue CCD filters Chroma used to sell a few years ago, they have a low cut-off (below 390nm) and very good transmission in CaK, but Chroma has changed the filter design meanwhile (as is documented in a thread somewhere on cloudynights), so for solar purposes only second-hand copies of the older version would do. Edmund Optics has a 393nm/10nmFWHM filter with very good transmission in CaK that I am using in combination with a blue CCD filter and a KG-3 IR blocker.

Regards,

Frank

[dhkaiser]

Like the AR with prom, thanks for posting.

[yltansg]

Hi Raf,

You have captured the different perspectives, from FDs to lovely proms in CAK, AR Zoom-in HA. The image with Baader B-CCD (telescope side) and a K-line filter looks great too.

Alfred

[solarGain]

krakatoa1883, Very interesting Ca-k images here.

[krakatoa1883]

dmund Optics has a 393nm/10nmFWHM filter with very good transmission in CaK that I am using in combination with a blue CCD filter and a KG-3 IR blocker.

thanks for your suggestion. I have found a 394 nm, suppose is the same ? https://www.edmundoptics.eu/f/hard-coat ... ers/13837/

[p_zetner]

Beautiful set of images, Raf!

The CaK proms are an impressive accomplishment and the H alpha proms are nicely sharp. I tried to image the CaK proms a few days ago but could only glimpse them faintly...not enough intensity to image (at the focal ratio I was using).

If you are searching for an alternative blocking filter for the Lunt etalon, I think you'll need a bandpass on the order of several Angstroms, not nm. I think the EO 10nm bandpass will be too large, probably passing several etalon transmission modes. I'm using an Omega "2.2 Angstrom" (nominal) CaK filter with good success but the quality can vary from filter to filter and they are USD299! I think Stuart Green (Carbon60) is using one of these as well.
https://www.ebay.com/itm/Optical-Filter ... 48b01c44f8

Looking forward to the results of your experimentation.

Best of luck.
Peter

[LTHB]

dmund Optics has a 393nm/10nmFWHM filter with very good transmission in CaK that I am using in combination with a blue CCD filter and a KG-3 IR blocker.

thanks for your suggestion. I have found a 394 nm, suppose is the same ? https://www.edmundoptics.eu/f/hard-coat ... ers/13837/

Yes, that's the EO filter I use, "393nm" was a typo, sorry!

And Peter is right, of course! The EO filter plus a Chroma blue filter plus a KG-3 IR-blocker together are my ERF for CaK (i.e. no substitute for the Lunt blocking filter, but possibly for the Baader blue CCD filter or the violet/blue filter at the front end of the Lunt units), sitting 10cm or so in front of the CaK blocking filter, which comes from a PST in my setup. Sorry if that wasn't clear!

Unfortunately the CaK-PSTs are hard to find these days, as you probably know. Buying an Omega CaK-filter is, as far as I can tell, a bit of a gamble, with odds not too good for the buyer. Peter and Stu have been lucky! I got a copy that is usable in about half of the field of view, and even there it is quite uneven. It's a pity that none of the filter manufacturers is offering a decent CaK filter!

[DeepSolar64]

A nice prom. And I missed it due to rain.

[marktownley]

Good pictures Raf, and a good post with lots of useful info!

[krakatoa1883]

Thanks for comments and for useful info about a candidate BF for my Lunt etalon.

Yes, 10nm FWHM seems too wide for an effective BF, however the K-line which is around 8nm gives only a slightly lower contrast compared to the original Lunt so may be that something around few nm could be enough as one can see from this topic where I have found some measures on the Lunt BF.

Thanks for suggesting Omega filters, I already have an Omega Ca-H which is acceptable but very dark.

[marktownley]

The EO 394/10 has a >=85% transmission compared to 75% for the K-line so offers some marginal gains.

[krakatoa1883]

Thanks Mark for the advice. Sky today is very hazy however I made a couple of video just to show the kind of problem I am facing with the BF.

This below is an image with K-line + B-CCD in front of the etalon

k crop.jpg (32.19 KiB) Viewed 2010 times

and this is with the original Lunt BF assembly

bf crop.jpg (23.6 KiB) Viewed 2010 times

The latter seems to have more contrast and seems more "calcium-like" as one can expect from the narrower FWHM of the BF, however it is completely blurred. Note also the "smeared" appearance of the image.

Same scope, sampling, sky, seeing, capture parameters, no. of stacked frames (100), only a minimal UM for both with same radius and same contrast.

[Montana]

I had exactly the same with my Lunt CaK module, I sent it back and got it fixed, it is a totally different animal to how it was before, I don't know why I persisted with it so long. However I thought it was always the seeing

Alexandra

[krakatoa1883]

Thanks, Alexandra, very interesting. I am planning to remove both BF filter to find a better tilting position as I think the problem is that.

[marktownley]

I think there is astigmatism with the 2 lunt mini ERFs that sit ahead of the main filter...

[krakatoa1883]

May be a mix of coma and astigmatism, more coma perhaps. Today the seeing is horrific however I couldn't resist to make further tests and these are the results:

taka betwn bf and eta arrow.jpg (28.87 KiB) Viewed 1942 times

while rotating the BF assembly by 90° gives this

taka betwn bf and eta 90deg arrow.jpg (29.08 KiB) Viewed 1942 times

However placing the barlow BEFORE the blocking filter makes the scope slower as seen from the BF and cures most of the problem

taka before bf.jpg (61.59 KiB) Viewed 1942 times

The scope is a f/6.9, quite sensitive to any error introduced by elements placed well before focus.

[John]

The barlow in front of the BF certainly gives a marked improvement. I have been thinking of trying a barlow or telecentric before my Lunt CaK module after Mark Townley reported the benefits of using a telecentric in front of his CaK homebrew. Are you using a 2" barlow? Were you using the original front Lunt ERF or the B-CCD and K line filter?

John

[krakatoa1883]

Hello John, I used of the original BF assembly of my Lunt module. The Barlow is a Takahashi extender, an air-spaced doublet with only 20 mm of free aperture. Given the dramatic improvement I had I am now planning to purchase a larger focal extender, possibly of a telecentric type.

[marktownley]

All good and productive experiment Raf!