Repairing a CaK PST

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Repairing a CaK PST

Post by Montana »

Christmas morning with nothing to do apart from cook a turkey just for the two of us.

We are taking slow and small steps and I used the hairdryer on the eyepiece holder for 5 minutes and then the hubby could easily shift the eyepiece with the boa.

This is what it looks like
DSC09958b.jpg
DSC09958b.jpg (1.57 MiB) Viewed 5557 times
I am presuming this looks sick?

and now I need to buy one of these? ;)

https://www.amazon.co.uk/Neewer%C2%AE-P ... CQKROFZVDU

I have a replacement filter which was kindly sent to me for free from Apollo :bow2 I also have a Baader Venus filter for Christmas too for emergencies.
Please let me know if I am on the wrong track.
Merry Christmas
Alexandra


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Re: Repairing a CaK PST

Post by marktownley »

A lens spanner is essential equipment for any solar astronomer.

That filter is definitely sick. Replace it and see how you get on. If you can get away with replacing the one in the gold tube then all good.


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Re: Repairing a CaK PST

Post by Montana »

OK, so progress so far...

A lens spanner is on order for the eyepiece holder. Apollo, is the filter you sent me a replacement for this filter?

Tonight we heated the gold tube with a hairdryer and the tube came off quite easily. There was no locktite but it came away from the black box. Is this a bad thing? we heated again and tried to take the blue part off but there is nothing to grip apart from my hands on one end while the Hubby pulls on the other. It is impossible to shift. Can I access the other lens from this end? or is this a lost cause?
DSC09966a.jpg
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filter before cleaning
DSC09967a.jpg
DSC09967a.jpg (623.72 KiB) Viewed 5506 times
after cleaning with 100% ethanol
DSC09969a.jpg
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I'm not sure which filter is which?

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Re: Repairing a CaK PST

Post by Bob Yoesle »

Hi Alexandra.

That appears to another case of peripheral filter deterioration in a secondary filter. Did you use the CaK for visual, imaging, or both?

I'd be leery of using the scope visually with any DIY filter system replacements. You can salvage the crucial "yellow" filter which isolates the CaK emission and make your own CaK module quite easily. Most of us started with a 50 mm Baader Blue CCD filter as an "ERF," then the Baader K line, and finally the PST CaK yellow filter - makes an excellent imaging-ONLY system. You can get fancier with other filters down the road, such as short-pass and long-pass filters, etc.

viewtopic.php?t=16455


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Re: Repairing a CaK PST

Post by marktownley »

Woop Woop!!!

This is the easiest fix ever. Wait until your lens spanner arrives and then just unscrew the collar in your pictures in the end of the yellow tube. The rusted filter you have pictured is what you need to replace.

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Re: Repairing a CaK PST

Post by Montana »

My lens spanner arrived this afternoon and we unscrewed the filter and popped it out.

This is my filter sat next to Apollo's filter. Mine didn't really have a gold and silver side compared to Apollo's and so we put silver towards the CaK filter and gold towards the black box. I think that is probably right. Hopefully if it is sunny tomorrow I will see how it fares before touching the eyepiece filter.

At this point I must say what a kind and very lovely gentleman Apollo is. He has always treated me with the utmost kindness and has always been very willing to help and give me advice. Giving help and advice is the most absolute kindness you can ever give someone and I truly value this above all. I respect him greatly. OK sometimes his communication skills can be difficult on the forum but then not everyone is blessed with these skills and sometimes they can be mis-interpreted when written down. I greatly value his generosity in sending me this CaK filter and I wanted to make it known how kind he can be. He also has some fantastic CaK pictures and animations, some of the best I have ever seen but you have to watch Stargazer's Lounge for that (sadly).

Anyway, my filters (you can guess who's is who's).
IMG_9558a.jpg
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Re: Repairing a CaK PST

Post by Montana »

:hamster: I finally got some brief sunshine at lunch to test the CaK PST and at first I was ecstatic as I have raised the imaging exposure from 86.8ms at 1x to 23.12ms by changing this one filter. to Apollo's.

However, joy went to sadness as I think I have ******* it. I think the pentaprism is now out of alignment as it is badly out of focus one side and in focus at only at the very far right :( :( :( my baby is probably dead? I knew it was a long shot but at least I gave my baby the best life possible.

ImageSun_130612_31_12_2020 by Alexandra Hart, on Flickr

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Re: Repairing a CaK PST

Post by marktownley »

No, it's never dead just needs to be reborn. Do away with the black box and screw a SCT focuser onto the end of the gold tube, use it straight through.


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Re: Repairing a CaK PST

Post by Montana »

Thanks Mark, however, what about the eyepiece bit, surely that filter has a function and needs to be added?

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Re: Repairing a CaK PST

Post by Montana »

Do you mean something like this? how do you know it will screw on the end?
https://www.firstlightoptics.com/skywat ... copes.html

Oh yes, and how would it attach to my mount?

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Re: Repairing a CaK PST

Post by marktownley »

THere might be an easier way here...

You can unscrew the gold tube and EP holder from the CaK PST, well simply 'swap' the black box from your donor PST (the one you're using with the C11) - just a case of unscrewing the ep holder off that one. You're getting a dab hand with a hair dryer and PST mods. Would keep the 'form factor' of the original CaK PST, just be badged differently...


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Re: Repairing a CaK PST

Post by marktownley »

Montana wrote: Thu Dec 31, 2020 5:45 pm Thanks Mark, however, what about the eyepiece bit, surely that filter has a function and needs to be added?

Alexandra
Just use your Baader K-line that is all that is needed.


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Re: Repairing a CaK PST

Post by Montana »

Oh yes!!! good idea!!

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Re: Repairing a CaK PST

Post by Montana »

Done, hopefully test tomorrow :)

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Re: Repairing a CaK PST

Post by Bob Yoesle »

Hi Mark and Alexandra,

I might be missing something, but have some concerns.

"Thanks Mark, however, what about the eyepiece bit, surely that filter has a function and needs to be added?"

If I'm not mistaken, the eyepiece holder objective-side filter is an ITF for IR blocking, and has obviously "rusted." It will continue to function for IR blocking, but will have a considerable decrease in contrast and detail due to the oxidized silver layers. I'm assuming it would have been designed for CaK transmission at 394 nm. The other filter on the eyepiece-side is a 5 nm CaK bandpass filter.

"You can unscrew the gold tube and EP holder from the CaK PST, well simply 'swap' the black box from your donor PST (the one you're using with the C11) - just a case of unscrewing the ep holder off that one. You're getting a dab hand with a hair dryer and PST mods. Would keep the 'form factor' of the original CaK PST, just be badged differently.."

I would think that Alexandra's poor imaging CaK shown in her picture is mostly - if not completely - due to a sagging pentaprism alignment issue, which is a relatively easy fix in and of itself (and ultimately could also affect the H alpha PST box). The pentaprism just needs removal and resetting with a better adhesive, and/or periodic refurbishment if it does re-sag. https://www.cloudynights.com/topic/5308 ... try7109716

"Just use your Baader K-line that is all that is needed."

Without a CaK ITF for long IR - wouldn't the Baader K Line filter alone be unsuitable for visual use? Wouldn't you need to add a KG3 or 5, or BG38 filter in this case?
filterkurveklinebaader.gif
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KG & BG UV-IR blocking.jpg
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Imaging is one thing, but I again caution about using any replacement filters for visual use unless you're absolutely sure you are making up for the spectral characteristics of the removed filter components.


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Re: Repairing a CaK PST

Post by marktownley »

No visual going on here at all Bob!

Reseating the sagging pentaprism is an option as you say, swapping a 'sagged' black box for a 'good' black box is also an easy way of doing it. ;)


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Re: Repairing a CaK PST

Post by DeepSolar64 »

Alexandra,
I am curious how you fare with the repair job. Best of luck. Keep us posted.

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Re: Repairing a CaK PST

Post by Montana »

Thanks guys :) I am starting to get a bit lost with all this as I don't understand really what bits does what ;)

Bob, this is imaging only, I have never used my eyeball on the CaK PST as it has always been too faint. I love my two PSTs as they sit side by side on my Merlin mount and are really quick and I can swap out the camera between the two in 5 seconds and virtually have side by side imaging in less than 10 minutes. Great for British winters or travelling.

Apollo, no need to apologise, my CaK PST was dead before I started as it was getting so dark even the camera could barely image with it. Anything is better than nothing :) :) :) and something had to be done.

I was so gentle with the removal of the gold tube and eyepiece on the CaK PST by using the hairdryer first, the pentaprism must be so fragile if this is the problem. The new Halpha PST for the PST mod was nearly destroyed by the removal of the etalon, 3 rubber boas and days of puff so I hope this black box is still OK?
The weather forecast was for pure blue skies all day today (predicted all week) so what do we have, total cloud :( I have the bedroom pre-cooled and everything ready to test too.

So questions:
1. First we have gold tube + objective, we then have CaK filter (looked OK from what I could see). We then have Apollo's filter, what does that do?

2. We then have the eyepiece filter, what does that do? am I right in thinking I can remove this filter, leave it blank and put either a Baader K line filter in my camera nose or a Baader U filter. I have both but I think my K-line is a bit dodgy as I have never had a clear image through it (always blurred).

3. If Apollo's filter does turn out to be as sad as my filter is there a replacement?

Many thanks for all you help, I really do appreciate your kindness and help.

Alexandra


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Re: Repairing a CaK PST

Post by marktownley »

Montana wrote: Sat Jan 02, 2021 12:26 pm If Apollo's filter does turn out to be as sad as my filter is there a replacement?
Yes, it really is simple. Using your lens spanner remove Apollos replacement filter (if it doesn't work), remove all the 2 filters from the eyepiece holders. Then when you image use the K-line or the venus filter on the nose of the camera. If using one doesn't work, and you'll know because the image will all be washed out with no detail, it is because there is a IR leak, in which case use the K-line and Venus filter stacked on the nose of the camera. That will work.


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Re: Repairing a CaK PST

Post by Montana »

Question for Bob, I've been looking at the pentaprism in the above link and yes it is angled but I thought the standard was angled? this was to remove reflections, it shouldn't be dead straight? this is an image of my H-alpha PST pentaprism and it works great at this angle.
ImagePST problems by Alexandra Hart, on Flickr

I will have a look at the CaK one now

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Re: Repairing a CaK PST

Post by Montana »

This is the CaK pentaprism, it looks very similar to the H-alpha one above
DSC00042a.jpg
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I think I need to do lots of filter assessments, so need some Sun for longer than 15 minutes. Today's Sun never came at all.

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Re: Repairing a CaK PST

Post by Bob Yoesle »

Hi Alexandra,

They do look pretty much the same, so I don't know why exactly one would be better than the other - other than perhaps 656 nm is less susceptible to tilt aberrations than 394 nm. It also could be there is a variable amount of misalignment as the pentaprism moves through its range of travel when focusing. I'd first straighten out the CaK prism to see if any improvement occurs, and evaluate the prism orientation through its range of travel (remove the eyepiece barrel and observe for any shift in the image seen through the pentaprism).

To be honest, if I used a PST for imaging (or even visual), I'd dispense with the pentaprism focusing as Mark has described and use a suitable R&P focuser, using the filters as Mark has outlined. You might also consider a 50 mm "ERF" type filter ahead of the objective - something like the Baader Blue CCD or Astronomic filters commonly used for this purpose.

On the other hand, rather than scrapping the box and adding an R&P focuser, especially since it seems you like the form-factor of the PST - and I haven't seen anyone do this yet, but think it would easily work - remove the entire pentaprism focusing system from the black box and put in a standard right angle diagonal prism or diagonal mirror in instead. As a bonus, the removal of the pentaprism should give you some significant additional back focus, and you could remove the eyepiece holder and add a helical focuser instead. There appear to be a few suitable non-rotating models available, including these:

https://agenaastro.com/shop-by-brand/zw ... dfEALw_wcB

https://www.amazon.com/Astromania-Preci ... B07FDPMZ98

There would be virtually no change in the appearance of the PST(s) this way, and they could be stored in the OEM case(s). Seems like this would involve minimal materials and effort to put into effect with readily available parts...


Addendum. I also remembered this thread for making the PST box a straight through using a helical focuser, which you might also like to consider:

https://pbase.com/andy_dodson/evoloutio ... ter&page=1

And here's another good thread featuring Bart's PST CaK mods:

viewtopic.php?t=25213


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Re: Repairing a CaK PST

Post by Montana »

Sunshine :hamster: so had a good testing session this afternoon.

The pentaprisms are coated differently and I had the same sneaky suspicion as Apollo that this may not work.
ImagePST Pentaprisms by Alexandra Hart, on Flickr

and correct, it does not work to swap bodies. I had absolutely nothing come through to the camera, black black and black.

So I swapped back to the CaK body and removed Apollo's filter in the gold tube. I placed the camera in and could immediately see the Sun, it was very very bright. After knocking the exposure right down I could see that I had a double disc like a ghost and out of focus. This looked like very bad UV/IR out of focus bleed through. So to answer the unanswered questions above, the filter in the gold tube seems to block stay UV/IR light and is absolutely necessary. So I tried the Baader U filter on the camera nose and total blackness followed. It completely blocks everything. I had a suspicion this would also be the case as it blocks light above 380nm. I have no idea how Eric uses it for Calcium K?

So I placed my dodgy Baader K line filter in and wow! perfect! I took 2000 frames and checked stacking and focusing and it was great. I even tried 1.6x and that too was great.

So at 1x my old filter exposure was at 86.8ms
Apollo's filter at 23.12ms (but sadly suffered astigmatism)
Baader K line as replacement 7.975ms

I am very happy indeed, at 1.6x the exposure was 21.62ms so this is a huge shift in usability although I see now I get a reflection with this Barlow. I will try with a 2x Barlow on the next outing (just like the olden days :hamster: ).

These images are the best Calcium K images I have taken for a couple of years I think, so I am a very happy bunny today.

However, mystery eyepiece filter? no idea what that does and I won't disturb that for a few years until I am suffering again. At the moment I am very pleased with the imaging capability. I am also happy I finally have a use for my Baader K line. At low magnification it works very well, maybe it is just bad at high res with the TEC140 and C11. It now has a happy home with the PST.

ImageSun_122203_03_01_2021 by Alexandra Hart, on Flickr

ImageSun_122203_03_01_2021_f colour by Alexandra Hart, on Flickr

ImageSun_123010_03_01_2021_a by Alexandra Hart, on Flickr

Thanks everyone for all your kindness and help, I am very happy indeed and glad I have learned all this from you :)

Alexandra


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Re: Repairing a CaK PST

Post by marktownley »

Whoop Whoop! I knew between us all it would sort out. Good work team!!!

You know what my suggestion is going to be... Remove the mystery filter in the EP holder and see what effect it has, might even shorten exposure time? Worth a go one of those days you have time to pass.

Even made a use of that badly behaved K-line filter of yours.

All good!


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Re: Repairing a CaK PST

Post by MapleRidge »

Great new Alexandra, good to know you are back in business with with the K-Line filter !!!

What is the cause of the bright circular spot in the third pic...is this one of the ghost images or a reflection maybe?

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Re: Repairing a CaK PST

Post by Montana »

Brian it looks identical to a reflection I get with the TeleVue 2.5x Powermate when using Calcium K. So I guess it is the same thing, the Baader K line has a mirror surface so I think it reflects light back and hits an element in the barlow lens and then back again. This was solved in the powermate by moving the distance of the camera 4cm higher up. However, this does not change the powermate magnification, but this would probably change a Barlow and also the distance would probably render it not able to reach focus with a PST. So I am going to try my 2x Barlow instead and have my fingers crossed :)

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Re: Repairing a CaK PST

Post by MapleRidge »

Alexandra...that reflection reminded me of that problem, but wasn't sure if you had enough focus travel to reach focus when the spacing was increased.

Nice to see it back to life ;)

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Re: Repairing a CaK PST

Post by Bob Yoesle »

Hi Alexandra,

Looks like you're back in business.

I haven't yet had a chance to to try it, but the Baader K line filter has two elements; one tilted and the other not. You might try to disassemble the filter and use only the tilted element. From the little I have seen of this it will not significantly affect the filters out-of-band blocking ability, but may help remove the ghost reflection. Due to becoming a single stack filter, the filter transmission will increase - and therefore image brightness - resulting in shorter exposure times and better freezing of seeing effects.


Baader K line tranmission.jpg
Baader K line tranmission.jpg (150.99 KiB) Viewed 5847 times
Christian Viladrich et.al.

When my weather improves I'm interested in trying this myself...


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Re: Repairing a CaK PST

Post by Montana »

Very interesting, thanks for the great info Apollo :hamster:

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Re: Repairing a CaK PST

Post by Montana »

Today I have had another play around with the filters (very unlike me) to see what the nose piece filters do.

I unscrewed the nosepiece filter off the bottom and had a good clean with ethanol and lens wipe. By eyeball it looked good when I looked at the Sun through it. The second filter further up looked just like clear glass to me so I cleaned it and left it where it was (nervous about permanent changes).

So I tested an image with various combinations of the Baader K-line, a Baader U, Baader blue CCD (at the front of the scope as an ERF) and the nose piece filter.
Baader K-line is 390-398nm
Baader U Venus filter 320-380nm
Baader Blue CCD ?-?
CaK PST nosepiece filter ?-?

Image2021-01-09 CaK Nosepiece filter test by Alexandra Hart, on Flickr

Probably better to click through to Flickr. The result is I am sticking with the CaK nosepiece filter and Baader K-line combo :)

The 1.6x Barlow reflection is almost gone when I unscrew it from the camera by about 5mm. I can still achieve focus and it isn't too bad

ImageSun_134025_09_01_2021 1-6x a by Alexandra Hart, on Flickr

Seeing was pretty terrible today with a milky white haze and passing clouds so I am pleased I got this far.
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Re: Repairing a CaK PST

Post by marktownley »

The CaK PST #1 filter and the K-line is a killer combo.

My CaK project this year is finding the best double stack combo. I bought another CaK PST off ebay in the autumn and plan is to strip the #1 filter from it, and then from my existing CaK DS filter find which combination of filters works best. However that requires sunshine and time, so probably spring :lol:


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Re: Repairing a CaK PST

Post by Montana »

Mark,

I already thought you had 2 CaK PST's? From my experience the filter in the eyepiece is quite crucial, the one in the gold tube not so much.
When I went to visit Luca in Italy he had a CaK modded device from a PST and I always thought the bandpass was less than my Lunt. More like the image with the Baader K line alone with the CaK gold tube filter together. I think the eyepiece filter seems quite crucial for getting a tighter bandpass and I expect his mod did not include it.

Apollo, yes I am surprised about the Baader U filter (unless I bought the wrong one?). Certainly mine is not pink, it is green. I questioned Eric about how old was his filter but he never replied. I was suspicious from the point of ordering but everyone was saying it was fine.

It was bought for me as a Christmas present so it is a 2020 edition of the filter and it quite clearly states that it blocks above 380nm. When using it with the CaK eyepiece filter it is black, no light. When the eyepiece filter is removed it just passes pure out of focus UV and nothing you can do to get it in focus. This is why I think this CaK eyepiece filter is quite crucial to reaching correct narrow bandpass. However, it must leak a little UV as adding the Baader K line with an 8nm wide filter tightens it up.
DSC00050 a.jpg
DSC00050 a.jpg (793.75 KiB) Viewed 5749 times
It seems to be no longer for sale on the 365 Astronomy website so I cannot show you the link.

All very interesting, but my useless Baader K line filter has gone into service and now I have a useless Baader U filter. I guess I need to image Venus with it :lol:

Alexandra


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Re: Repairing a CaK PST

Post by Carbon60 »

At least you've found a combination that works, Alexandra. I'm pretty sure the first filter (pointing at the Sun) blocks most wavelengths except for those close to 393 nm (this one appears blue) and the eyepiece filter passes all wavelengths except for those below about 393 nm (this one appears yellow as it is absorbing blue and passing green/red light. The cutoff wavelength of each filter is very close so as to allow the transmission of a narrow band of light at the required 393.4 nm when the filters work together. That's how I understand my Lunt module works, so I'd expect it to be the same with the PST. Apologies if this has already been discussed in this long thread.

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Re: Repairing a CaK PST

Post by Bob Yoesle »

Hi Stu,
I'm pretty sure the first filter (pointing at the Sun) blocks most wavelengths except for those close to 393 nm (this one appears blue) and the eyepiece filter passes all wavelengths except for those below about 393 nm (this one appears yellow as it is absorbing blue and passing green/red light. The cutoff wavelength of each filter is very close so as to allow the transmission of a narrow band of light at the required 393.4 nm when the filters work together. That's how I understand my Lunt module works, so I'd expect it to be the same with the PST.
Depending on the viewing angle, the first filter can appear blue or a reflective gold in my CaK PST(s). It is the clear yellow in transmission (purplish in reflection) dichroic filter which is the essential filter of the PST at the 394 nm region. Brian Stephens (Tucson Coronado / LUNT) refers to this filter as the CaK "blocking filter." He states this PST filter would now days be very expensive to secure - $1500.00 - $2000.00 USD. So LUNT has now placed smaller versions of this filter in the eyepiece barrel of the LUNT CaK diagonals, and they are no longer even making the largest version due to the expense. LUNT eventually may find these CaK units to be too expensive to make considering the demand, and has hinted at their potential demise... so I would get one while one knows they can.

The transmission of this dichroic filter looks like this:

Lunt CaK Etalon_wide blocking filter.PNG
Lunt CaK Etalon_wide blocking filter.PNG (42.79 KiB) Viewed 5730 times

Note this dichroic filter IS NOT an etalon as whoever made this spectrographic measurement labeled it.

Christian Viladrich uses instead a very narrow Barr bandpass filter for the same purpose, and he and Apollo have explored other hard-coated filter options from Chroma Tech and Alluxa, but these are also expensive and cost a minimum of about $2500.00 USD to produce, and production appears fraught with peak transmission CWL consistency difficulties.

The remaining filters in the PST are apparently a combination of cut-off, bandpass, and ITF's to render the image relatively bright enough and safe for eyeball imaging. Unfortunately they appear to be soft-coated and can or will deteriorate within a few years time. Replacing these with the right hard-coated filters apparently would make all the difference.

For me this has meant the move to a do-it-yourself CaK module solution (allowing a greater aperture to be used), but there's no reason these can't be incorporated into the PST - especially if it is intended for imaging only.

With my soon-to-be revised DIY CaK module, I'll be double stacking two PST "blocking filters," and using a "stew" of other mostly hard-coated filters to isolate the 393.4 nm transmission.

An Edmund fused silica 1/4 lambda hard-coated 390 45 florescence bandpass filter, followed by either an Andover KG3 or tilted BelOptik UV/IR KG3 for long IR, will replace the Baader Blue CCD filter as an "ERF":

390 nm Bandpass 45 FWHM.jpg
390 nm Bandpass 45 FWHM.jpg (128.67 KiB) Viewed 5730 times

After these, and based on as yet to be made observations, I will have to decide if I will use Apollo's hard-coated Chroma Tech 393.37 0.1 (requires tilting to be on-band), a Baader K line (single stacked vs. the normal DS as posted above), or an Edmund fused silica hard-coated 400 nm short pass filter to further isolate the blocking filter's transmission while maintaining the highest transmission possible for achieving the shortest exposure times and best contrast.

400 nm SP OD 4 curve.jpg
400 nm SP OD 4 curve.jpg (132.68 KiB) Viewed 5730 times

I'm not sure what the cut-on point of the slightly tilted BelOptik UV/IR K3 will be, but this Edmund short-pass and UV/IR KG might be the ideal pre-filer for the PST blocking filters:

UV IR KG3 w 400 SP v K Line.jpg
UV IR KG3 w 400 SP v K Line.jpg (203.54 KiB) Viewed 5687 times

The Edmund 400 nm SP combined with the BelOptik UV/IR KG3 filter appears to offer the possibility of significant improvement in transmission to the K line as a pre-filter, especially if the UV/IR KG3 filter slightly blue-shifts when tilted. The Chroma Tech filter requires significant tilting to come on-band, and I'm not sure of its transmission percentage at that point. Indeed, most of these filters will need to be slightly tilted to minimize retro-reflections and optimize their their performance, so I've had to source some Baader-based filter-tilters from Bart and BelOptik in addition to Apollo's generous provision of SkyBenders to hopefully accomplish this task. Putting all these together in an acceptable mechanical arrangement will be a challenge, and will likely require additional machining work.

Filter tilters.jpg
Filter tilters.jpg (259.47 KiB) Viewed 5730 times
Last edited by Bob Yoesle on Tue Jan 12, 2021 3:23 pm, edited 3 times in total.


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Re: Repairing a CaK PST

Post by Montana »

I've just heard back from Eric, he got his Baader U many years ago, so I guess pre 2009.

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Re: Repairing a CaK PST

Post by DavidG »

Like others that own a CaK PST, the filters will hazy over with age. So far the main yellow one in the OTA is still in good shape but the blocking filter in the eyepiece tube had hazied over. I took it into work and measured it. It was only passing less than 2% at the CaK wavelength . I was still able to see an image in the scope but had to cover my head with a dark cloth and let my eyes dark adapt to see the image.
I had worked with Maier Photonics on other projects and sells an ITF filter that works very well in H alpha PST so I looked on their website to see if anything might work. Maiers does offer a 393nm filter that looked very promising. I sent them the scan of the filter from my CaK PST and ask how their filter would match up. Chris Maiers sent me back the scan of his filter and sent me one to try. The Maiers filter is larger than the original and I was able to mount it in place with a couple of O-rings. The scan of the Maier's filter showed it transmits around 50% at CaK wavelengths and is block into the IR out OD4.
The image is now much brighter and I can see the image visually without covering my head with a cloth. The image is now back to the brightness I remember it when the scope was new.
https://maierphotonics.com/bandpassfilters.aspx

- Dave
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Maier CaK filter.jpg
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CaK PST Blocking Filter.jpg
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Re: Repairing a CaK PST

Post by Bob Yoesle »

Thanks for finding this Dave!

I believe the primary yellow dichroic filter is hard-coated and pretty resilient.

The only other issue for visual use would be how far out the Maier filter is blocked for IR out to about 3000+ nm. It might be necessary to employ a KG3 filter for this purpose when the other ancillary filters have deteriorated.

Bob


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Re: Repairing a CaK PST

Post by Montana »

Thanks Dave, that is really interesting. Can I ask whether you have imaged through this at all? I have been using a Baader K line filter in replacement to the busted blocking filter but my surface contrast is much reduced to what I used to get with the original blocking filter. So I was wondering if this filter is giving a similar tight bandpass as the original. I would say that my PST is no longer 2.2A, but much greater (to my sadness). I would like to get back to 2.2A again somehow :(

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Re: Repairing a CaK PST

Post by DavidG »

Bob,
Here is what is listed on Maier's site for his 393 filter that I used
393 Bandpass Filter - sulfur line gas chromatography
Center wavelength=393 nm +/- 2 nm
Bandwidth=13 nm +/- 2 nm
Size=12.0 mm dia. x 5.0 mm thick
Out of band blocking > optical density 4.0 (xray to 2000 nm)
Coating type= Non hydroscopic

So it is pretty well blocked into the IR. There is also another filter directly below the eyepiece in my CaK PST and it seems to be IR blockers as well.

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Re: Repairing a CaK PST

Post by DavidG »

Alexandra,
I have not imaged through my CaK with the new filter but it is on my list and will post images when I do. I can say that the image is much bright and I see it visually pretty well and even see some CaK features on the disk when I cover my head with dark cloth.

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Re: Repairing a CaK PST

Post by DavidG »

Hi All,
Happy 2023 ! I finally had both some free time and clear skies to use my repaired CaK PST that I used a Maier Photonics filter to replace the bad one in mine. Visually today I could see the CaK features and was very pleased with the images it was producing with my ZWO 120 monochrome camera.
Here is an image made from a short 10 sec video I took and my good friend Matt Considine processed for me. Matt said it is only lightly processed. The images were taken around 3:30pm so the Sun was low and the seeing wasn't great but again I very pleased at how well the CaK features are visible.

- Dave
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Re: Repairing a CaK PST

Post by Montana »

Is this the one you bought David https://maierphotonics.com/bandpass-filter.aspx

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Re: Repairing a CaK PST

Post by DavidG »

Alexandra,
Yes that is the Maier's filter I'm using.

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Re: Repairing a CaK PST

Post by marktownley »

Good fix!


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Re: Repairing a CaK PST

Post by estra »

Hello Alexandra

Did you buy the Meiers filter? Did your Ca Pst recover the contrast you were looking for?

Best regards
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Re: Repairing a CaK PST

Post by Montana »

Hi Paulo,
Yes I did buy the Maier filter although it was very complicated to buy and took a few weeks to place the order because the website didn't work for overseas customers. My PST is much better than it was with the Baader Kline in but I have always had my worries that my Baader K line is faulty. It is still not as good as it was when brand new, but at least it is usable now. Here is an image taken in July
Image2023-07-19 CaK solar disc f colour b by Alexandra Hart, on Flickr

I need to take a photo of how I fixed the Maier in the eyepiece :)

Alexandra


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