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C14 without corrector


Chrb1985

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I have a c14 with cracked corrector. This acctually don't seem to affect the image at all but it really annoys me since u want everything to both work perfect and also look perfect. I already know that the c14 won't work without correcting the spherical abberation or dispersjon so I was wondering if someone her knows if the Baader Hyperion 38mm eye piece with t2 threads in both ends will do as good job as the original corrector? It says it designed especially to correct spherical dispersion.

I have already made a spider, but I'm hesitant to buy the Baader eyepiece since it's kinda expensive and since I don't know if it will work. 

I have been in touch with Baader and they said that they did not have a clue if it would work it not. They acctually told me to ask amateur astronomers on forums.

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The eyepiece may correct a small amount of spherical abberation, but an SCT design without a corrector has an insane amount, possibly more than 10 waves. In short it won't work at all, the scope probably won't even form an image.

Leave it well alone!

Edited by Astronomist
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44 minutes ago, Earl said:

Afiak correctors and mirrors are matched, nothing that I am aware of it will correct it.

In principle it could be corrected in software. The HST had this very problem when first launched --- absolutely enormous spherical aberration. Stellar images were an arcsecond across, when they should have been at most a tenth of that. Richardson-Lucy deconvolution was used with remarkable effect until the COSTAR corrective optics was installed.

Of course, this is useful only for imaging and mention of the word "eyepiece" suggests that is not the area of interest.

I concur: leave well alone.

Addendum: if all you want to use it for is photometry then poor focussing, SA, etc, are generally of minor importance. Back in the day I had a 18" Dobsonian light bucket with significant SA. As all I wanted to do was estimate variable stars it didn't much matter, though it did cost me perhaps 0.2 to 0.5 magnitudes at the faint end. The scope was dirt cheap so it was a price worth paying. It was certainly not worth having the mirror refigured.

 

Edited by Xilman
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As you have noticed, the crack doesn't affect the performance.  If you don't like the look of the crack keep the cover cap on during the day and only look through the eyepiece end at night.       🙂

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3 hours ago, michael.h.f.wilkinson said:

It is not quite clear what eyepiece you are referring to. There is a Hyperion 36 mm (no 38mm) Aspheric, but that just means it uses aspheric surfaces for better correction, not that it will correct spherical aberration of the telescope.

Hmm okay. Well yeah that's the one I'm talking about. It says on the description that it will correct for that. And Baader also said that it corrects aspheric dispersion. But anyway I really appreciate your feed back!

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3 hours ago, Xilman said:

In principle it could be corrected in software. The HST had this very problem when first launched --- absolutely enormous spherical aberration. Stellar images were an arcsecond across, when they should have been at most a tenth of that. Richardson-Lucy deconvolution was used with remarkable effect until the COSTAR corrective optics was installed.

Of course, this is useful only for imaging and mention of the word "eyepiece" suggests that is not the area of interest.

I concur: leave well alone.

Addendum: if all you want to use it for is photometry then poor focussing, SA, etc, are generally of minor importance. Back in the day I had a 18" Dobsonian light bucket with significant SA. As all I wanted to do was estimate variable stars it didn't much matter, though it did cost me perhaps 0.2 to 0.5 magnitudes at the faint end. The scope was dirt cheap so it was a price worth paying. It was certainly not worth having the mirror refigured.

 

Hmm okay. All this was really interesting. So if I go ahead and try this, you think I can even get a planet in to focus? And if I do. Is this software even free? If it possible to correct it later with software,.well that's sound amazing!  But again my concern than is the focus.. hmm please do fill me in on more if you would not in mind.

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5 minutes ago, Chrb1985 said:

Hmm okay. All this was really interesting. So if I go ahead and try this, you think I can even get a planet in to focus? And if I do. Is this software even free? If it possible to correct it later with software,.well that's sound amazing!  But again my concern than is the focus.. hmm please do fill me in on more if you would not in mind.

You may, or may not, be able to get it into focus, whatever that means when the image has severe SA. Perhaps it means the apparent disk of a star has minimal diameter but perhaps it means when the bright core of the disk has minimal diameter, or perhaps something else.

My experience with RL deconvolution is that it can halve the apparent size of a star without introducing objectionable artefacts, though it does destroy the photometric properties. If you have a very good model of the point spread function and enough photons it can do better. In the HST case they had an almost perfect model and could lengthen exposure times to improve the signal to noise ratio.

Richardson-Lucy, IME, is not so effective on extended images such as planets. Maximum entropy tends to do a better job, again IME, because it assumes that the sources are extended and of uniform brightness until proven otherwise.

By all means have a play. It is very easy to defocus the telescope and then attempt to refocus the images in software. It is only slightly more difficult to introduce spherical aberration, by installing a zero-power spherical lens (i.e both surfaces have the same curvature with one concave and the other convex) before the camera. These experiments can be done with any telescope, including your slightly damaged example.

I still wouldn't advise fiddling with the corrector plate until you are absolutely certain you know what you are doing and the consequences of doing so. To reach that point will take a lot of research, experimentation, and time. All of the algorithms and some of their implementations are freely available.  I can almost guarantee that you will not find a turn-key solution to your particular problem and you will have to learn signal processing, inverse theory, coding, and software development processes. Not trying put you off - quite the reverse as I encourage people to learn new skills - but neither do I want you to walk in to a challenging environment with your eyes closed.

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Can you give us a better idea of the extent of the crack?  My concern is that if it is less than a radius, releasing any stress on the corrector by attempting to remove it might exacerbate the situation.    🙂

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3 hours ago, Xilman said:

You may, or may not, be able to get it into focus, whatever that means when the image has severe SA. Perhaps it means the apparent disk of a star has minimal diameter but perhaps it means when the bright core of the disk has minimal diameter, or perhaps something else.

My experience with RL deconvolution is that it can halve the apparent size of a star without introducing objectionable artefacts, though it does destroy the photometric properties. If you have a very good model of the point spread function and enough photons it can do better. In the HST case they had an almost perfect model and could lengthen exposure times to improve the signal to noise ratio.

Richardson-Lucy, IME, is not so effective on extended images such as planets. Maximum entropy tends to do a better job, again IME, because it assumes that the sources are extended and of uniform brightness until proven otherwise.

By all means have a play. It is very easy to defocus the telescope and then attempt to refocus the images in software. It is only slightly more difficult to introduce spherical aberration, by installing a zero-power spherical lens (i.e both surfaces have the same curvature with one concave and the other convex) before the camera. These experiments can be done with any telescope, including your slightly damaged example.

I still wouldn't advise fiddling with the corrector plate until you are absolutely certain you know what you are doing and the consequences of doing so. To reach that point will take a lot of research, experimentation, and time. All of the algorithms and some of their implementations are freely available.  I can almost guarantee that you will not find a turn-key solution to your particular problem and you will have to learn signal processing, inverse theory, coding, and software development processes. Not trying put you off - quite the reverse as I encourage people to learn new skills - but neither do I want you to walk in to a challenging environment with your eyes closed.

All I can say is wow.. I'm no stranger to jumping in with both eyes closed 🤦 and look where it lead me.. I really like the idea of fiddling around with different lenses.. but I guess I'll probably keep it as is.

Acctually there is one thing. If I buy I secondary from a classical cassegrain will this do anything, or make it better/worse? I'm really sorry for stupid questions..

But I think I read in a post on CN that a guy did that. He also bought a new smaller corrector and putted it in the baffle tube if Im not remembering wrong.

Thanks again for really good advices!

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46 minutes ago, Peter Drew said:

Can you give us a better idea of the extent of the crack?  My concern is that if it is less than a radius, releasing any stress on the corrector by attempting to remove it might exacerbate the situation.    🙂

I'm out walking the dog so I just took all of the ones from a folder. The one with the lazor is from when I centered the Optics. I know it really is NOT they way to do it. But as this is an really old scope I could not get the secondary of at the time so I had to do what I could and it acctually helped me to get it centers. But the manuals online from other c14 owners stat that the secondary HOLDER should be in place not the whole thing. I can tenner if I took of the mirror and just used the small center hole that holds the mirror or if I left the whole thing in place.

Just wanted to explain the lazor image. It's kinda cool that you can see the crack when it's defocused. 

I adde a few image taken with zwo 299mm and zwo 678mm of a house in my location faaaaar away.

And the moon. They are take with my phone of live view I think.

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Thank you for the images.  If my interpretation is correct then the corrector has two cracks.  There appears to be no more potential for further propagation of the cracks but I would be concerned that the lower arc segment could become detached if the corrector was released and reattaching it accurately might be impossible.  There is enough area of the corrector held in its original location to maintain its optical integrity, that's why the telescope still works.  From my experience of using and even making SCT's my advice would be to leave well enough alone, enjoy using the telescope and leave the question of alternative combinations as a hypothetical one of interest.    🙂 

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47 minutes ago, Peter Drew said:

Thank you for the images.  If my interpretation is correct then the corrector has two cracks.  There appears to be no more potential for further propagation of the cracks but I would be concerned that the lower arc segment could become detached if the corrector was released and reattaching it accurately might be impossible.  There is enough area of the corrector held in its original location to maintain its optical integrity, that's why the telescope still works.  From my experience of using and even making SCT's my advice would be to leave well enough alone, enjoy using the telescope and leave the question of alternative combinations as a hypothetical one of interest.    🙂 

I can clearly see three cracks. My advice would be leave well alone and handle and move it with care.

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17 hours ago, Xilman said:

In principle it could be corrected in software. The HST had this very problem when first launched --- absolutely enormous spherical aberration. Stellar images were an arcsecond across, when they should have been at most a tenth of that. Richardson-Lucy deconvolution was used with remarkable effect until the COSTAR corrective optics was installed.

Of course, this is useful only for imaging and mention of the word "eyepiece" suggests that is not the area of interest.

I concur: leave well alone.

Addendum: if all you want to use it for is photometry then poor focussing, SA, etc, are generally of minor importance. Back in the day I had a 18" Dobsonian light bucket with significant SA. As all I wanted to do was estimate variable stars it didn't much matter, though it did cost me perhaps 0.2 to 0.5 magnitudes at the faint end. The scope was dirt cheap so it was a price worth paying. It was certainly not worth having the mirror refigured.

 

Deconvolution is mathematically an ill-posed problem. Lucy-Richardson deconvolution is a more-or-less baseline method, but in all cases you need a very good model of the PSF, and very high signal to noise for it to work well. I get good results with LR deconvolution on solar and lunar data, where S/N is good, and wavelets don't seem to work as well. On planets, I prefer wavelet sharpening over LR deconvolution.

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12 hours ago, Peter Drew said:

Thank you for the images.  If my interpretation is correct then the corrector has two cracks.  There appears to be no more potential for further propagation of the cracks but I would be concerned that the lower arc segment could become detached if the corrector was released and reattaching it accurately might be impossible.  There is enough area of the corrector held in its original location to maintain its optical integrity, that's why the telescope still works.  From my experience of using and even making SCT's my advice would be to leave well enough alone, enjoy using the telescope and leave the question of alternative combinations as a hypothetical one of interest.    🙂 

Actually.. I already pulled it all apart and glued it with Loctite glass Glue. I used clamps to hold it in place. And as far as I can see and tell from just looking at it and collimation. It seems to be ok. I see a lot of videos og wonder glue types that is supposed to vondt i seamlessly but I really don't believe it. And I guess my attempt at gluing it is as good as It gets. I have installed 3 fans in the rear cell and cut out 2 holes in the front top of the OTA and Its not sealed properly in the cell and I have no filters in front of the fans inside the cell.. so I need to open the whole thing up again sooner or later. So when the time comes I will paint the whole thing and seal every little crack and make sure the filters are on snugg! Because right now I can spot some glue residue on the corrector and a ton of dust on the primary 🤦 I will also need to go through the re centraition (if that's  even a word) of the Optics from start to finish. I suspect that the corrector plate might be a tad off to one side. Now I can detach the secondary mirror to, so I can do it right this time.

If anyone have anye thoughts tips and advices for what I just mentioned please do let me know.

One more thing.. right now all 3 fans are blowing out. And I get condensation/dew on both sides of the corrector. I'm thinking (and seeing other doing this) to change Direction of 1 fan. So 2 blowing out and 1 blowing in. This is to keep the air flow/circulation inside the rear cell and not drag inn too much air from the heat plume vents in the front. Does this make sense to you guys?

 

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It seems that you have two choices, leave as is and use the telescope despite some defects, or continue with your experiments to see what happens next.  Advice so far has been based on expectations rather than direct experience which places you at the cutting edge of dealing with this issue.  Ultimately, your success or failure will be of use to others who might find themselves in a similar situation.  It might be worth giving the telescope the external insulation treatment currently favoured by many of the users of SCT's.

Whatever path you choose to take, good luck!      🙂 

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Hello, if you are going to remove the corrector plate again, I suggest of course clean and remove the glue, then using a very fat black marker to minimize  unwanted reflections, then re-glue only in spots. Also re-glue next to the secondary  mirror support.

You could  also use black tape all around. Make sure the flanges are clean. So sorry it happened.

If you are a model builder, you will understand-lots of patience, care, clean work space, steady hands, etc.
Yes I use to build a lot of models, plastic and cardboard (architectural models)

Good luck,

Edited by VNA
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10 hours ago, Peter Drew said:

It seems that you have two choices, leave as is and use the telescope despite some defects, or continue with your experiments to see what happens next.  Advice so far has been based on expectations rather than direct experience which places you at the cutting edge of dealing with this issue.  Ultimately, your success or failure will be of use to others who might find themselves in a similar situation.  It might be worth giving the telescope the external insulation treatment currently favoured by many of the users of SCT's.

Whatever path you choose to take, good luck!      🙂 

That's at least one good thing about the whole thing, that others can avoid some mistakes :)

This external insulation treatment. What is this? Not sure I know what you mean?

I did a lot of thinking yesterday. And I'm going to leave as is. But I think I will take the advice of using a black marker or rape to minimize reflections. That's sounded really smart. :)

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3 hours ago, Chrb1985 said:

That's at least one good thing about the whole thing, that others can avoid some mistakes :)

This external insulation treatment. What is this? Not sure I know what you mean?

I did a lot of thinking yesterday. And I'm going to leave as is. But I think I will take the advice of using a black marker or rape to minimize reflections. That's sounded really smart. :)

Wrapping the main tube externally with a couple of layers of "Reflectix" or similar insulating material is claimed by many to eliminate internal tube currents.   🙂

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On 07/10/2024 at 14:44, Chrb1985 said:

I have a c14 with cracked corrector. This acctually don't seem to affect the image at all but it really annoys me since u want everything to both work perfect and also look perfect. I already know that the c14 won't work without correcting the spherical abberation or dispersjon so I was wondering if someone her knows if the Baader Hyperion 38mm eye piece with t2 threads in both ends will do as good job as the original corrector? It says it designed especially to correct spherical dispersion.

I have already made a spider, but I'm hesitant to buy the Baader eyepiece since it's kinda expensive and since I don't know if it will work. 

I have been in touch with Baader and they said that they did not have a clue if it would work it not. They acctually told me to ask amateur astronomers on forums.

The SA of a C14 without its corrector would be of the order of 22 waves depending on the exact details of the mirrors. A lot worse than Hubble so you are wise to keep the corrector!

David

Edited by davidc135
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4 hours ago, Gonariu said:

I would ask Celestron for a quote to see if it is worth changing the corrector.

That might be easier said than done as I'm pretty sure the correctors are matched to the mirror sets.

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Celestron charged me £250 just for a new corrector plate for my RASA 11 after I accidently dropped it putting it on the mount. Luckily the corrector was the only part of the RASA itself that was damaged. They wouldn't let me change the corrector myself but insisted I sent it to Orion Optics to be repaired and aligned. (They sent the new corrector plate directly to OO). This is probably because the scope was still under guarantee and if I did it myself the guarantee would be void. OO did a good job and the scope is now as good as new. 😉 This repair  wasn't covered by the guarantee though.

I doubt whether correctors are matched to mirrors on mass produced scopes though. 🤔 Didn't affect the results with my replacement corrector.

Alan

Edited by symmetal
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