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Coronado PST disappointment


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I have bought a Coronado PST, but I only see a dark red Sun with no details whatsoever.

It is very easy to find the Sun, and the image looks clean and crisp. If I turn the focus knob far to either side, a certain blurriness is evident, as expected, but there is a large interval between the extremes where the image seems focused, judged from the sharpness of the edge.

But there is nothing to see except a featureless disc. I have checked against current solar pictures, and I should be have been able to see at least one sunspot - which should appear bright in the H-alpha light.

I have bought the extra etalon to make the PST double-stacked, but this changes very little (with the extra etalon, there is a strong ghost Sun, but it does not overlap the real image).

I have turned on all wheels on the etalons, and I imagine that I see more when I turn them right to the stop, but the image also turns darker, and I might imagine details that are not there.

Is this a common experience?

 I have a feeling that the image is too bright, and that I might see more details if I somehow let less light through, so next time the Sun reveals itself from behind the clouds that have hidden it ever since I got the telescope, I am going to use sunglasses, or use a polarizing filter.

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Reading your method of using the PST I cannot be sure that you are rotating the black ring but here is what I do with mine.

Always store the PST with the black ring turned fully clockwise to relive the pressure.

Find the sun and turn the focus knob under the eyepiece till the edge of the sun is nice and sharp

Rotate the black ring anticlockwise while looking at the suns surface. It will grow darker and before the end of travel is reached the suns surface will start to show detail. Do this slowly a little bit at a time

I find that not all types of eyepiece work well with the PST but 12 or 15mm are my favourite choice.

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It's no consolation, but I too have a PST and am also very disappointed with the view visually.

However, it can be very effective for imaging, and I often set it up with a basic QHY5 cam and just view the sun on the laptop. You can make various adjustments to see either the prominences or the surface features.

Here's an animation I did with it last year (colourised, as the QHY5 is mono).

51836778850_25db84205a_o.gif

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My local club has a Coronado PST. I’ve used it visually on lots of occasions, it gives excellent views.

If yours is giving poor views there’s several things to check.  The focus or tuner ring (or both) could need adjusting. You could be using too high a magnification. The sky conditions could be poor due to an unstable atmosphere or haze. How’s your own eyesight or glasses with everyday vision?   Or possibly your expectations are more than what you’re seeing, have a check online to find what other users can see visually.

Last possibility is a faulty unit.

Ed.

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Have you checked the condition of your itf filter? If you unscrew the eyepiece holder right at the base you can directly see the greenish side of the itf, it should be completely clear with no hint of mouldy like patches or misting or inconsistent finish. The eyepiece holder may be fixed tight with loctite if it hasn't been removed before. You can also just about see the itf if you open the side of the main box and look above the pentaprism into the underneath of the eyepiece tube but at such a shallow angle as theres not much of a gap to see it's hard to assess.

My own coronado pst is a bit "poor" but I know it is working because if the tuning ring is all the way anti clockwise (looking down toward the etalon) I can see prominences, I cannot however see sunspots when tuned anywhere else. The turning of the ring lets you see different features, you can't see them all at the same time. You also have the pentaprism height adjustment knob underneath the prism box which will adjust the alignment of the focus point. I personally think the image is very bright hence why it is difficult to discern anything. Also been persevering with it as I want to image though that is a different challenge entirely.

With solar (with my coronado anyway) you have to look very intently and focus your eye and concentrate on a particular spot, features will somehow magically appear (unless it's the tuning kicking in), but I find this concentration is required to discern anything. It's not like white light solar where sunspots are clear as soon as you look. It also helps just like when you're shielding your eyes from stray light at night to block your eyes from the external daylight (put a towel over your head, no seriously).

I've also found eyepieces make a huge difference, some good night eyepieces I tried don't work very well, some have hideous internal reflections which will make the viewing worse. The default cemax is okay, I've found my William Optics swan 9mm gives the best views.

Edited by Elp
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Hello @steenkh and welcome to SGL.

You don't say whether your PST was new or second hand.

I have had a PST for 17 years and although the front objective has the rust problem it still works great even with the double stack.

I would suggest the following. Use an eyepiece in the range 15 to 20mm to get a good full image of the Sun. Twist the big black ring to the right until it stops. At the moment there is a sunspot AR2934 which will appear on the right side of the disc. Now use the focus wheel to get sharp focus. Hopefully you will get that sharp image.

Now then turn the black ring to the left and you should start to see the image change. Look on the website GONG which will show the current Sun in Hydrogen Alpha and compare.

I would suggest leaving the double stack off until you are satisfied with the standard etalon.

Tells us how you get on.

 

 

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Thanks for all the comments. It is invaluable to get advice from people who know the instrument.

My PST is new, and I forgot to tell you that I have had very little opportunity to use it. After I received it, it has been cloudy whenever I have been at my summer house where the instrument is located. Once, when I had to visit the summer house to retrieve a charger that I had forgotten, the Sun was out, and I had ten minutes to set up the telescope and look through it for the first time before I had to pack up and leave with the next bus. The second time, we stayed there, and the Sun was shining nicely, but the garden was a swamp because of recent rain, and I could only set the PST up on a porch. I had to wait some hours before the Sun appeared from behind a large birch tree, and this time I managed about a quarter of an hour before clouds made observation impossible. That is a complete description of all my sessions with my new telescope!

I now realise that my second session which was much more deliberate, and where I had set up my AZ-GTi mount to track the Sun, was compromised by a wispy clouds before the Sun disappeared completely, and this might explain why I was disappointed. I have often used another telescope with white light, and sunspots were easily discernible even through thin clouds, and I expected the same to be true for H-alpha.

 I have also made the mistake of comparing my view with satellite pictures taken in other wavelengths. I’ll now only use the Gong pictures for reference, and I see that there really was very little to see when I had my opportunity. For instance, no protuberances.

So far I have only used the 18mm Coronado CEMax eyepiece that came with the telescope, but I have plenty of others to choose from.

The description of how to store the etalon with least stress, and how to turn it systematically during observation to find sweet spots for different features, is very useful.

I hope for more sunshine next time we go to the summer house, and with real luck, even cloudless nights. But Danish weather is traditionally lousy during winter (and the nights are too short during summer, so the PST was really bought for having something to do in summer).

 

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Hi steenkh. Commenting on your latest post.  I have H-alpha scope, and a regular refractor with Baader Astrosolar filter for white light.  I’ve used top end H-alpha scopes owned by others.  I’ve always found that sunspots are much better seen in white light rather than H-a.  Sunspots are seen with H-a but not as well. Of course for prominences, filaments and much else they’re only seen with H-a.

Sky conditions are crucial. Haze, depending on how much will reduce what’s seen.  Best will be with an obviously blue sky with the sun as high as possible.  Once when observing in H-a with a lovely blue sky I was a bit disappointed, until I realised I was viewing over the top of my wife’s greenhouse.  Heat turbulence rising from the greenhouse compromised what I could see. I moved the scope just a few meters therefore not viewing through that very local turbulence, and was delighted by the view.

Hoping you’ll get better views soon.

Ed.

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Good advice above. Sunspots are predominantly photospheric features rather than the chromosphere you are observing with an Ha telescope.  So they are much better in white light.
Unfortunately PST etalons are very variable, so no two examples will perform the same. But you should be able to resolve prominences and filaments easily with a double stacked scope. There is a possibility that your main etalon (filter) has decontacted. It’s always a risk, particularly if handled roughly during postage. So if you continue to see no detail, it’s important you tell the retailer and return the scope. 

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