Repairing a CaK PST

[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 (1.57 MiB) Viewed 4495 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 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

[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.

[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 (933.07 KiB) Viewed 4444 times

filter before cleaning

DSC09967a.jpg (623.72 KiB) Viewed 4444 times

after cleaning with 100% ethanol

DSC09969a.jpg (574.49 KiB) Viewed 4444 times

I'm not sure which filter is which?

Alexandra

[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

[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.

Mark

[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).

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DSC00015a.jpg (959.92 KiB) Viewed 4409 times

Alexandra

[Montana]

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.

Sun_130612_31_12_2020 by Alexandra Hart, on Flickr

Alexandra

[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.

[Montana]

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

Alexandra

[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?

Alexandra

[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...

[marktownley]

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.

[Montana]

Oh yes!!! good idea!!

Alexandra

[Montana]

Done, hopefully test tomorrow

Alexandra

[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 (135.08 KiB) Viewed 4327 times

KG & BG UV-IR blocking.jpg (122.6 KiB) Viewed 4327 times

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.

[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.

[DeepSolar64]

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

James

[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

[marktownley]

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.

[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.
PST problems by Alexandra Hart, on Flickr

I will have a look at the CaK one now

Alexandra

[Montana]

This is the CaK pentaprism, it looks very similar to the H-alpha one above

DSC00042a.jpg (1.05 MiB) Viewed 4276 times

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.

Alexandra

[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

[Montana]

Sunshine 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.
PST 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 ).

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.

Sun_122203_03_01_2021 by Alexandra Hart, on Flickr

Sun_122203_03_01_2021_f colour by Alexandra Hart, on Flickr

Sun_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

[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!

[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?

Brian