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Coronado PST issue(s)

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#1 Daphne S

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Posted 16 October 2021 - 05:23 AM

Hello, I'm hoping you might help me out here because after dismantling the bloody thing I am still at a loss!

 

I am  rather new to stargazing, and still sticking to manual alt-az star hopping under city sky (so far), which was actually the motivation to add a planet to the moon viewing and move from (quite enjoyable) white light observing with the lunt wedge on my tv-60, to my first H Alpha scope. I went for the PST instead of the Lunt 40 because it looked like a simpler build, which now I have seen up close is actually way simpler even then i suspected :-D 

 

Right out of the box, I noticed that the pst could only show some surface detail, a sunspot a n d tiny prominences at a single focus spot which was right at the (left) edge of the tube turn. Anywhere else to the right - nothing but a blank (but vibrant, which seemed to rule out rust issues) red disc. This looked odd because I was expecting to see either (prominence)-or(sunspots and granulation) but not all together, but there it was.  I thought maybe the tube turret had been mounted wrong, so I took the rubber band off and moved the stopping screw five holes to the left. The result is that the focus spot is now at the middle of the tube turn instead of the extreme left, but nothing else seems changed. I still see a blank disc when turning the etalon right or left of that point.

 

A second issue regards imaging - I'm not set up for ccd imaging and like I said don't use a tracking mount, but merely handhold a digicam to the eyepiece, still unlike my afocal moon captures with other scopes, the images i took through the pst all show the same - the disc at an angle, with a big blank spot, and granulation at the top only. as for prominences, unlike naked eye observing, the digicam captures either the prominence, or the inside of the disc (without moving the etalon though), but maybe that's as it should be (?) attached two sample pics (the second is a stack of nine consecutive captures) . Do these seem normal to you in a pst?

 

Naturally suspecting filter rust i had a close look at the blocking filter and the itf, and found no edge or center rust on them however, both feature golden specks which I wonder about (phone pics attached!) - oxydation? something else? 

 

Lastly, the prism doesn't look  well aligned to me. I have tried to nudge it a little but it returns to its original place.  However I didn't remove the screw (there is a big blob of glue round the contact area)- was that a prerequisite to successful adjusting of the chips? The misalignement isn't huge, but I wonder if it might be sufficient to produce that angled image I see in the eyepiece (?) - more phone pics of the prism attached

Attached Thumbnails

  • stacked sun_H Alpha.jpg
  • _DSC3958.JPG
  • IMG-0052.jpg
  • IMG-0053.jpg
  • IMG-0034.jpg
  • IMG-0035.jpg

Edited by Daphne S, 16 October 2021 - 12:30 PM.


#2 MalVeauX

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Posted 16 October 2021 - 08:33 AM

Heya,

 

Hard to tell from these thumbnail size photos of the disc, but it looks like I'm seeing AR2882 and a prominence, maybe some chromosphere network. This is good because it means your etalon is not decontacted (that would be disastrous). But, it looks like the uniformity on your etalon is poor, which is very common with these. You'll need to tune the ring back and forth until you get the most uniform view of the whole disc before even attempting to evaluate much more here.

 

As for your ITF and BF, those photos are completely blurry and out of focus on top of being thumbnail size, so can't really answer anything there. But, in the mean time, you can just look through them at bare sky or a light source and see if there's patches of bright/dark or artifact or obstruction in the view, which would indicate problems there too. Typically its not your BF that has issues, typically its the ITF (that larger filter).

 

The internal prism on PST are almost always misaligned and wonky. They're free floating and slide on grease from a threading bolt that pushes it. At focus the edge of the prism that is facing the etalon assembly should be orthogonal approximately to it. A bunch of sag and tilt will make focusing challenging. This is probably the easiest thing to fix and sort since it's not an optical issue, but simply placement issue.

 

Overall, getting a PST over a Lunt 40 is simply not saving you anything; PST are trouble, no support, bad ITF (always, they WILL be bad if not now they will be later), awful focusing system and just generally poorly made things. If you can return this to the seller, I would. I wouldn't accept this thing. For a few dollars more you can get a brand new Lunt 40 without these problems, with full support from Lunt instead of 3 separate components that are all having issues. I realize this may be ugly to hear and I'm sorry to sound negative, but just giving you the blunt skinny of what it's like to deal with a used PST (or any used etalon frankly) that is 100% always a big gamble to get anything remotely decent in working order.

 

Very best,



#3 Daphne S

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Posted 16 October 2021 - 09:06 AM

Thanks for your detailed reply, much appreciated!flowerred.gif  

 

I can't seem to take a focused pic of the golden specks on/in the BF and ITF  but there is quite a lot of them on both filters.

 

Indeed, very poor uniformity - now i've changed the etalon screw position, i can see either pin sharp prominences o r some surface detail (just spent an hour sweating in the sun trying to find the sun spot to focus on, until i realised its hidden from sight today!), unlike before when both could be seen together. When i move the scope a little, detail moves to another spot in the sun disc and so does the blank part, so I am guessing that's not a faulty filter causing this but simply the very narrow focusing ability of the pst (bad news for stackless imaging, good to know for observing).

 

Prism : how does one fix this confused1.gif  if i separate the screw from the chip and manage to align it, how would the screw go back in? how much does the current misalignment actually impact the image?

 

As for returning the PST well  I already got stung with steep import tax and of course the return would be added to that. Btw I decided I would give the pst a try after I stumbled on some threads complaining about pink halos, blank sun disc (ha!) and poor focus on the Lunt 40/50!


Edited by Daphne S, 16 October 2021 - 12:44 PM.


#4 vincentv

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Posted 17 October 2021 - 01:46 PM

As a side note you seem to be mixing terms.

 

Focus: This is what you adjust with the silver knob that moves the prism up and down. You don't need a sunspot to focus. The solar limb when detuned (no h-alpha details visible) is sufficient.

 

Etalon tuning: You adjust this when turning the rubber ring that's on the golden tube. Sounds like you already figured out a thing or two. Make sure to move it *slowly*. If you move it too fast details can pop-in and out of view before the eye has time to adjust. We are somewhat blind to this end of the spectrum and it takes some experience to make most of it.



#5 Daphne S

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Posted 17 October 2021 - 02:46 PM

er , yes I do use the fine focus knob after the slowish etalon tuning! however since most of the sun disc is annoyingly blank on my pst, a detuned etalon isn't much help and that's when a nice sun spot,nicely focused, is useful (it usually allows me to see some detail around it)
 
speaking of which, I have moved the etalon tuning screw back to its original position (no change in the views) and am now wondering if flocking tube and maybe prism housing (?) might help me see more detail, or if this (attached today's views) is all I am ever going to get with my pst? did anyone try flocking?

Attached Thumbnails

  • _DSC4128_pe.jpg
  • _DSC4125.JPG

Edited by Daphne S, 17 October 2021 - 02:57 PM.


#6 DAVIDG

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Posted 17 October 2021 - 08:52 PM

 Your ITF filter looks totally rusted over to me. It should be perfectly clear red and I believe this is your problem.  As you stated your prism is also out of alignment. The two 90 degree face should be perfectly parallel to inside sides of the housing.  You need to slowly twist the prism past the position were it would be aligned and let it relax back to a position were it is aligned.

 

              - Dave 



#7 MalVeauX

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Posted 17 October 2021 - 09:04 PM

did anyone try flocking?

I would suggest you do not go that far. There's nothing flocking will help with in a system that only allows 656.28nm to pass. If there were reflections you would see them readily. If there are none, its because there are none. I see no indication of a reflection in your images at all, robbing contrast. Your issue(s) is mostly the etalon coming on band and potentially your ITF degraded to the point of killing all contrast (super common thing with these).

 

Even with a relatively poor sample of a PST, you should be able to come on band and see the chromosphere network somewhere. So odds are, you're not tuned to HA or its not coming on band, and/or its your ITF.

 

We could easily tell you what's what if you can get a clear image of your ITF with it facing some sky in daylight. This would also be a much easier fix if it's this.

 

Very best,



#8 Daphne S

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Posted 18 October 2021 - 02:38 AM

hello again, so to recap.

I had a chat with Oliver (Beloptik). Turns out that -

the prism is ok, it doesnt need to be perfectly parallel to the eyepiece but that a slight tilt
is needed. so no issues there.

the ITF is pristine. slightly sharper pic attached. mirror on both sides (mine isn't red, there are various kinds in the pst line according to Oliver) is fine except for those little flecks which were probably dust settling in at manufacture.

the chronosphere IS visible, but only at about one third of the sun disc. that's my problem!
not coming on band? or no full disc detail possible with a pst?

remember these are afocal pics taken with the digicam against the eyepiece you are seeing,
the eye does see more detail but again, only at a relatively small portion of the disc at a time.
the stacked image i posted at the top of this thread is closer to what the eye actually sees at the eyepiece

about flocking : I d o see tons of reflections all the time with my narrow fov plossls!thats what made me think
of flocking in the first place. a dark cloth over the head and ep makes them go away(except in the horrid plossl that came with the pst)

Attached Thumbnails

  • IMG-0056.jpg

Edited by Daphne S, 18 October 2021 - 03:00 AM.


#9 MalVeauX

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Posted 18 October 2021 - 07:46 AM

Hrm,

 

Well, that's not good news. A bad ITF would have been a simple fix. If your ITF is fine and your focus system is fine, then the only other thing that could have problems is the etalon itself. It may be seated improperly in its compression chamber, it may be in the process of decontacting, etc.

 

In a working good PST the disc fits within the sweet spot (its a 20mm clear aperture etalon and a 40mm objective producing a sweet spot around 0.5 degree or so which should allow a full disc in the sweet spot, just small image scale of course).

 

If you're seeing chromosphere features in one area and the rest goes off band and gets really bright, that means you're likely having some tilt in the etalon chamber system and that the plates are not getting uniform pressure so there's bad banding and interference. You'll need to inspect this or have someone familiar with this stuff to check it out maybe.

 

Unfortunately none of this is uncommon with a PST.

 

Very best,



#10 DAVIDG

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Posted 18 October 2021 - 08:45 AM

 That is not true of the prism.  When it is tilted you get astigmatism in the image. Owners  of the Calcium K version of the PST discovered this when they tried to image with the them. You can raytrace  the design and also see that tilting a penta prism introduces astigmatism. 

    You need to  take closer pictures of the ITF and showing the view through the filter Many times they are totally and uniformly rusted over so to the untrained eye they look fine.  In the images of the red side of the filter I can see a layer in the filter and that indicates that is full oxidized and rusted over. You  should not be able to see any layers  in the filter especially at  low angle. It should appear as a clear red filter at any angle.  Flocking will do no good. You said you see many reflections. Are they multiple images of the Sun ? If so that indicates a decontacted Etalon.

    I have had  two PST's for  at least 15 years now and have work on over 20 and they are very much capable of the producing full disk images that are on band with great detail and compare well with my 60mm Lunt.  If your unit contains the original ITF and is over 3 years old the odds are very good the ITF is bad at least that has been my experience.

 

                   - Dave 



#11 Daphne S

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Posted 18 October 2021 - 08:53 AM

David. my ITF is fine. it isnt red btw, both sides are mirorred. the red color in the first pic i posted was a reflection of the BF.
the prism seems ok too. of course i see only a single sun (thankfully) and no decontacted etalon either.
this is a brand new (well, old stock I guess) PST...

Edited by Daphne S, 18 October 2021 - 08:55 AM.


#12 Daphne S

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Posted 18 October 2021 - 08:59 AM

lol its not all bad news, I have just seen the entire disc within the sweet spot finally, a small miracle performed
with the help of a nd filter (which still wasn't strong enough! for the bright disc) and a thicker black cloth over ep and head.

the disc wasn't blank after all - it was glare in was looking at in the center. since i always placed the disc right
in the middle, the glare prevented me from seeing anything but the slightly darker edges in the eps i was
using (18mm and 15mm). Today I switched to 10mm, then 6mm and 5mm. while high power made the spicules
compete with my floaters, i finally saw some stuff.

but with a more comfortable ep, such as a 60 fov 12mm, the glare at the center washes out most of the image.
also, filaments and proms looks like tiny hairs in 40mm, let alone the rest of the surface. its really
a very small perspective for observing unless one images on a screen, which holds zero attraction to me
under israeli scorching sun!

As for the imaging- I've just been told that any afocal hand held image in H Alpha will cause tilting and
uneven illumination aka, worsen the glare. Looks like I'll stick to moon imaging...

My conclusion is that H Alpha observing should be way more enjoyable with a 60mm objective!

Edited by Daphne S, 18 October 2021 - 10:19 AM.


#13 DAVIDG

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Posted 18 October 2021 - 12:00 PM

 If your PST is working correctly you should easily see images that compare well to the near real time images on the GONG site https://gong2.nso.ed...figs/hAlpha.cfg

 The GONG network uses H-alpha telescopes  with 28mm apertures so almost half that of 40mm PST.

 

                    - Dave 



#14 Daphne S

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Posted 18 October 2021 - 12:05 PM

David I see somewhat better images than these with the pst however they are not in easy to view BW but in contrastless fiery red which makes a difference

#15 DAVIDG

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Posted 18 October 2021 - 03:43 PM

David I see somewhat better images than these with the pst however they are not in easy to view BW but in contrastless fiery red which makes a difference

 All I can say is that I have been into solar observing for many years and have designed, built and restored many  solar instruments. When a PST is working correctly there is no issue with contrast and brightness and the image are as good or better then the GONG ones  without any trouble in obtaining them.  In my experience when people are having   issues with them it has been the ITF. I have seen "new" PST's  with  completely rusted over filters.  There are many threads here were people have replaced their  ITF and found a vast improve in the detail and contrast. Here is  a link to just a few  I think you should take a close look at your ITF to be sure  it is as good as you believe because you can be missing some great solar images if it is not functioning correctly. 

 

https://www.cloudyni...ion-pst-owners/

       

              - Dave 


Edited by DAVIDG, 18 October 2021 - 03:43 PM.


#16 billtootsuds

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Posted 18 October 2021 - 08:49 PM

An image from my pst, Maybe it help's give you a idea of what you should be able to see.

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  • 2021-10-07-gimp.jpg

  • mike4271 likes this

#17 Daphne S

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Posted 18 October 2021 - 09:45 PM

thanks for sending this picture, it brought home the fact that you're all in the right, zero contrast, even though the banding is present,
cannot mean but one thing - rusted filter. and sure enough i found the exact angle which shows it - it was the
mirror surface that fooled me looking intact.
onto the beloptik replacement filter... btw how do you open that filter holder short of ordering a special tool for that too?

Attached Thumbnails

  • unnamed.jpg

Edited by Daphne S, 19 October 2021 - 11:37 AM.



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