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Can't solve this aberration.

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#1 FiveByEagle

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Posted 05 December 2022 - 11:20 AM

Hello and Good Morning!

 

Over the last two weeks, I have been amassing and optimizing my 8SE OTA for planetary imaging. new IR pass/block filter(s), RACI, Bob's Knobs and a new barlow for the 462MC.

 

However, even with collimating the scope and getting excellent concentric rings and the centered donut - there was what appears to be a bar on the side of the donut. If you can imaging the "power" symbol on many PC's and electronics, that was similar.

 

Thinking that my imaging train was the issue, I stripped it down piece by piece. Barlows, filters, diagonals, all the way until it was just the 462MC into the visual back (no diagonal) and when I found Mars, there were three of them at close focus.

 

My gut tells me that the Bob's Knobs have knocked the secondary out of the alignment, but with being able to lock in the concentric rings and centered donut I kind-of doubt it. It looks like there is something physically sticking into the OTA but I can't locate it.

 

Attached is an image that is about 1 turn out of focus. Not fully out to show the donut, but about halfway back to focus. 

 

 

Unknown 17
 

 


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#2 dcaponeii

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Posted 05 December 2022 - 11:25 AM

You’re no going to get anywhere in planetary trying to collimate using out of focus donuts. Since you are imaging you should use Metaguide and an IR Pass filter so you can collimate AT FOCUS. See the FAQ pinned to the forum for additional details on collimating for planetary imaging.
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#3 FiveByEagle

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Posted 05 December 2022 - 11:27 AM

You’re no going to get anywhere in planetary trying to collimate using out of focus donuts. Since you are imaging you should use Metaguide and an IR Pass filter so you can collimate AT FOCUS. See the FAQ pinned to the forum for additional details on collimating for planetary imaging.

Trust me. Ive read that already. It just says "make sure your scope is very well collimated"

 

Do a CMD+F and search the word collimate on the FAQ - 7 results, none of which are actual guides.


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#4 Borodog

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Posted 05 December 2022 - 11:28 AM

Hello and Good Morning!

 

Over the last two weeks, I have been amassing and optimizing my 8SE OTA for planetary imaging. new IR pass/block filter(s), RACI, Bob's Knobs and a new barlow for the 462MC.

 

However, even with collimating the scope and getting excellent concentric rings and the centered donut - there was what appears to be a bar on the side of the donut. If you can imaging the "power" symbol on many PC's and electronics, that was similar.

 

Thinking that my imaging train was the issue, I stripped it down piece by piece. Barlows, filters, diagonals, all the way until it was just the 462MC into the visual back (no diagonal) and when I found Mars, there were three of them at close focus.

 

My gut tells me that the Bob's Knobs have knocked the secondary out of the alignment, but with being able to lock in the concentric rings and centered donut I kind-of doubt it. It looks like there is something physically sticking into the OTA but I can't locate it.

 

Attached is an image that is about 1 turn out of focus. Not fully out to show the donut, but about halfway back to focus. 

 

 

 

An actual image instead of a picture of the screen would be helpful. My first thought is that it's probably just a heat plume from a scope in thermal disequilibrium. Do you have the scope insulated with Reflectix? If not, do so yesterday if possible.


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#5 FiveByEagle

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Posted 05 December 2022 - 11:34 AM

An actual image instead of a picture of the screen would be helpful. My first thought is that it's probably just a heat plume from a scope in thermal disequilibrium. Do you have the scope insulated with Reflectix? If not, do so yesterday if possible.

The scope was outside for 2-3 hours in the ~20º weather prior to imaging. Only the camera came to the show later.



#6 CharLakeAstro

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Posted 05 December 2022 - 11:42 AM

Agree, looks like a heat plume.

 

An actual image instead of a picture of the screen would be helpful. My first thought is that it's probably just a heat plume from a scope in thermal disequilibrium. Do you have the scope insulated with Reflectix? If not, do so yesterday if possible.



#7 Borodog

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Posted 05 December 2022 - 11:45 AM

The scope was outside for 2-3 hours in the ~20º weather prior to imaging. Only the camera came to the show later.

20°C or 20°F?

 

If the former, you should be fine. If the latter, 3 hours is not enough. Either way, insulate the scope.



#8 RedLionNJ

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Posted 05 December 2022 - 11:59 AM

Trust me. Ive read that already. It just says "make sure your scope is very well collimated"

 

Do a CMD+F and search the word collimate on the FAQ - 7 results, none of which are actual guides.

You're not wrong, there. There is absolutely no guidance regarding HOW to judge collimation (not even a link) in the FAQ.  We'll get that addressed.  Andrew?


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#9 KiwiRay

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Posted 05 December 2022 - 12:29 PM

http://www.astrophoto.fr/collim.html


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#10 yock1960

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Posted 05 December 2022 - 12:29 PM

You’re no going to get anywhere in planetary trying to collimate using out of focus donuts. Since you are imaging you should use Metaguide and an IR Pass filter so you can collimate AT FOCUS. See the FAQ pinned to the forum for additional details on collimating for planetary imaging.

Really? Huh, I must be a lot luckier than I tought. I think it may have more to do with what focal length you are using, when collimating.

 

Steve


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#11 FiveByEagle

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Posted 05 December 2022 - 12:49 PM

Really? Huh, I must be a lot luckier than I tought. I think it may have more to do with what focal length you are using, when collimating.

 

Steve

I tried at native f10 and then at f20 w/ the barlow.

 

That line didn't move in the disk, and rotated with the camera. Shouldn't a heat plume... plume? Like there was an obvious schlieren affect going on from my hand, but the line was static and unmoving.



#12 Borodog

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Posted 05 December 2022 - 01:36 PM

I tried at native f10 and then at f20 w/ the barlow.

That line didn't move in the disk, and rotated with the camera. Shouldn't a heat plume... plume? Like there was an obvious schlieren affect going on from my hand, but the line was static and unmoving.


You mean when you rotated the camera the feature stayed fixed on the screen?

If so you have your answer. There’s a problem with something attached to the camera, either the UV/IR cut filter or the AR glass, or whatever else is attached to the camera that rotated with it relative to the scope.

A heat plume is laminar, by the way, and does not necessarily show any obvious internal motion in its shape.

#13 Borodog

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Posted 05 December 2022 - 01:40 PM

Rereading again it seems like you probably meant that the feature rotated on the screen when you rotated the canera, meaning it is scope side. It really does look like a heat plume.
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#14 dcaponeii

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Posted 05 December 2022 - 02:30 PM

Really? Huh, I must be a lot luckier than I tought. I think it may have more to do with what focal length you are using, when collimating.

 

Steve

No, you're just underestimating how critical IN FOCUS collimation is to your planetary imaging results.  If you are not collimating IN FOCUS then in most cases your images can still improve.


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#15 Tulloch

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Posted 05 December 2022 - 03:27 PM

You’re no going to get anywhere in planetary trying to collimate using out of focus donuts. Since you are imaging you should use Metaguide and an IR Pass filter so you can collimate AT FOCUS. See the FAQ pinned to the forum for additional details on collimating for planetary imaging.

 

Trust me. Ive read that already. It just says "make sure your scope is very well collimated"

 

Do a CMD+F and search the word collimate on the FAQ - 7 results, none of which are actual guides.

 

You're not wrong, there. There is absolutely no guidance regarding HOW to judge collimation (not even a link) in the FAQ.  We'll get that addressed.  Andrew?

Hi there, you are correct, there is no step-by-step guide on how to collimate in the FAQ. That was deliberate on my part, I was writing a guide to "planetary imaging", not "how to use your telescope". There are hundreds of websites, guides, books etc that talk about the correct way to collimate your scope, and each style (Newt/SCT/RC/etc) has their own particular method to obtain "correct" collimation. The FAQ does address collimation with the slightly cheeky catch-all phrase "Learning how to collimate your scope is an important skill for planetary imaging" but doesn't really provide links to how to do it for your particular style of OTA. It's also probably important to mention that precise collimation is even more critical for planetary imaging than DSO imaging.

 

Having said that, section 18 at the end does provide some links which include sections on how to collimate (Darryl's website, Christophe's book, Damien's DVD) but maybe that could be a little more specific in section 11.

 

The FAQ does need a liitle freshen up anyway, there are a couple of small things I want to update and I can include some links in the collimation section as well. I'll start up a new thread requesting updates to the FAQ and see what I get.

 

Thanks, Andrew


Edited by Tulloch, 05 December 2022 - 03:30 PM.

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#16 yock1960

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Posted 05 December 2022 - 03:52 PM

No, you're just underestimating how critical IN FOCUS collimation is to your planetary imaging results.  If you are not collimating IN FOCUS then in most cases your images can still improve.

No doubt. But I think people should have a workflow that works for them and keeps it an enjoyable activity. I like to spend my scope time imaging and I limit my scope time, for various reasons, one of them being...I get bored after a while. lol.gif

 

Steve


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#17 FiveByEagle

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Posted 06 December 2022 - 10:43 AM

Hi there, you are correct, there is no step-by-step guide on how to collimate in the FAQ. That was deliberate on my part, I was writing a guide to "planetary imaging", not "how to use your telescope". There are hundreds of websites, guides, books etc that talk about the correct way to collimate your scope, and each style (Newt/SCT/RC/etc) has their own particular method to obtain "correct" collimation. 

 

Section 18:8

 

"The Cloudy Nights planetary imaging forum probably has the answer to anything not covered here – just search it or create a new topic!"
 

 

Well, that is why I am here. I am fairly familiar with collimation, but this odd shaped spike in my disk has me scratching my head thoroughly. I will start with leaving the scope outside for the full evening prior to imaging and try that.

 

Sadly, my EQ6R does not have a HC, so I am purely trying to do all of this with a laptop trackpad. I was unaware that insulating a scope was a thing, Luckily it seems cheap so I can try it fairly quickly.

 

For the "heat plume" Can someone provide examples of what this looks like? I should have taken more images of the aberration versus just trying to fix it, I realize that now.

 

For example - https://www.youtube....h?v=uen0M9b5Qpc - that looks very very small in comparison. My line was leaving the disk entirely, and not staying within the concentric rings.



#18 RedLionNJ

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Posted 06 December 2022 - 10:56 AM

If I understand correctly, the appearance of a heat plume should "switch sides" as you roll through focus and out the other side. Did this occur?

 

I have a hard time differentiating between heat plumes and just plain poor (roiling) seeing with my own SCT. These days I have it wrapped in Reflectix, installed permanently in an observatory and I open the roof AND turn on a couple stand fans at least an hour before starting to use it. At least that way, I can be fairly sure the terrible previews are indeed due to poor seeing :(



#19 Borodog

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Posted 06 December 2022 - 12:33 PM

Section 18:8

 

"The Cloudy Nights planetary imaging forum probably has the answer to anything not covered here – just search it or create a new topic!"
 

 

Well, that is why I am here. I am fairly familiar with collimation, but this odd shaped spike in my disk has me scratching my head thoroughly. I will start with leaving the scope outside for the full evening prior to imaging and try that.

 

Sadly, my EQ6R does not have a HC, so I am purely trying to do all of this with a laptop trackpad. I was unaware that insulating a scope was a thing, Luckily it seems cheap so I can try it fairly quickly.

 

For the "heat plume" Can someone provide examples of what this looks like? I should have taken more images of the aberration versus just trying to fix it, I realize that now.

 

For example - https://www.youtube....h?v=uen0M9b5Qpc - that looks very very small in comparison. My line was leaving the disk entirely, and not staying within the concentric rings.

 

I don't believe you ever answered whether your "20 degrees" was Celsius or Fahrenheit. If it is the latter, and your scope was kept inside, you will most likely not reach thermal equilibrium. At all. You can leave a big scope out 4 hours, 6 hours, or more, and still be chasing equilibrium in the extreme cold. Just insulate the scope. It is a thing. It is in fact a huge thing. A properly insulated large SCT or Mak can be used for high resolution imaging immediately. If you are really in 20°F weather, I would recommend 2 layers of Reflectix.

 

You can do a google image search on something like "SCT tube current" or "SCT heat plume" or something and see examples. They can be quite varied in appearance, depending on a few factors like the angle of the OTA and if or where the plume is splashing on the corrector plate, as well as the actual temperature difference. A slight temperature difference between the OTA and the baffle tube will lead to a mild tube current, while a large temperature difference will drive a very strong current. 


Edited by Borodog, 06 December 2022 - 12:33 PM.


#20 Tulloch

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Posted 06 December 2022 - 03:38 PM

Section 18:8

 

"The Cloudy Nights planetary imaging forum probably has the answer to anything not covered here – just search it or create a new topic!"
 

 

Well, that is why I am here. I am fairly familiar with collimation, but this odd shaped spike in my disk has me scratching my head thoroughly. I will start with leaving the scope outside for the full evening prior to imaging and try that.

 

Sadly, my EQ6R does not have a HC, so I am purely trying to do all of this with a laptop trackpad. I was unaware that insulating a scope was a thing, Luckily it seems cheap so I can try it fairly quickly.

 

For the "heat plume" Can someone provide examples of what this looks like? I should have taken more images of the aberration versus just trying to fix it, I realize that now.

 

For example - https://www.youtube....h?v=uen0M9b5Qpc - that looks very very small in comparison. My line was leaving the disk entirely, and not staying within the concentric rings.

Your abberation is rather unusual, I've never seen anything like it before. While it might well be a heat plume, it does look very large compared to what I normally see.

 

I produced an image showing the heat plume on a star I was using for collimation, the stacked image looks like this. I believe the solid segment shows the effect of the heat plume (upside down on this image), so nothing like what you have.

 

2020-04-27-1118_0-L-DSO_AS_P50_l6_ap1_Driz30 ps1.png

 

While the people on this forum might be able to help, maybe there are other forums that could be better (Cats and Casses?)

 

Andrew


Edited by Tulloch, 06 December 2022 - 03:39 PM.

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#21 dcaponeii

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Posted 06 December 2022 - 04:17 PM

Your abberation is rather unusual, I've never seen anything like it before. While it might well be a heat plume, it does look very large compared to what I normally see.

 

I produced an image showing the heat plume on a star I was using for collimation, the stacked image looks like this. I believe the solid segment shows the effect of the heat plume (upside down on this image), so nothing like what you have.

 

attachicon.gif2020-04-27-1118_0-L-DSO_AS_P50_l6_ap1_Driz30 ps1.png

 

While the people on this forum might be able to help, maybe there are other forums that could be better (Cats and Casses?)

 

Andrew

You've given a great example of heat plume to the OP.  I think the reason his looks so different is because the GAIN is cranked up (or exposure I suppose) and blowing out the details.  The OP's image does not align with the statement that he is familiar with collimation.  Maybe the word but not the process, especially when it's applied to planetary imaging.



#22 FiveByEagle

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Posted 06 December 2022 - 04:42 PM

I don't believe you ever answered whether your "20 degrees" was Celsius or Fahrenheit. If it is the latter, and your scope was kept inside, you will most likely not reach thermal equilibrium. At all. You can leave a big scope out 4 hours, 6 hours, or more, and still be chasing equilibrium in the extreme cold. Just insulate the scope. It is a thing. It is in fact a huge thing. A properly insulated large SCT or Mak can be used for high resolution imaging immediately. If you are really in 20°F weather, I would recommend 2 layers of Reflectix.

 

You can do a google image search on something like "SCT tube current" or "SCT heat plume" or something and see examples. They can be quite varied in appearance, depending on a few factors like the angle of the OTA and if or where the plume is splashing on the corrector plate, as well as the actual temperature difference. A slight temperature difference between the OTA and the baffle tube will lead to a mild tube current, while a large temperature difference will drive a very strong current. 

Yea, closer to 15-20 F - 



#23 FiveByEagle

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Posted 06 December 2022 - 04:44 PM

You've given a great example of heat plume to the OP.  I think the reason his looks so different is because the GAIN is cranked up (or exposure I suppose) and blowing out the details.  The OP's image does not align with the statement that he is familiar with collimation.  Maybe the word but not the process, especially when it's applied to planetary imaging.

Again, it was a bad photo taken with a cell phone of a computer screen. If I would have thought to take a better one, I would have.

 

However, to my eyes the star was not blown out - I could still see the concentric rings. The image taken with the cell phone does not reflect that.

 

Next time I will screenshot - still learning PC, and didn't know how to do it as easy as CMD+F4 on a Mac. 


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#24 FiveByEagle

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Posted 06 December 2022 - 04:45 PM

You've given a great example of heat plume to the OP.  I think the reason his looks so different is because the GAIN is cranked up (or exposure I suppose) and blowing out the details.  The OP's image does not align with the statement that he is familiar with collimation.  Maybe the word but not the process, especially when it's applied to planetary imaging.

Also, as I had said in my post - I am familiar with what a "Heat Plume" is as well - however I had never seen one completely cross and exit the ring of a defocused star. I have only ever seen them stay within the rings.


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#25 dcaponeii

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Posted 06 December 2022 - 10:07 PM

Also, as I had said in my post - I am familiar with what a "Heat Plume" is as well - however I had never seen one completely cross and exit the ring of a defocused star. I have only ever seen them stay within the rings.

Yes I understand completely.  What you failed to understand is that out of focus stars are irrelevant for collimating at the accuracy needed for planetary imaging.  At BEST it will get you into the ballpark as long as it's a really LARGE ballpark.  You need to collimate IN FOCUS not OUT OF FOCUS.  But carry on, you'll get there eventually.  Andrew is updating his FAQ to include collimation links and that will help you a great deal.




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