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Difficulties Imaging

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#26 idclimber

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Posted 27 September 2020 - 09:58 AM

That looks like a good explanation. Reading back I noticed this:

 

I assume you mean guiding? Because no tracking on a 60 second sub woud be very difficult. In any case tracking seems to be the issue. Check your polar alignment, preferably the last thing you do after all mechanical adjustments. If you have no go-to you should check PA after moving to a target.

I think he may be using an Alt-Az mount?  At this image scale I would expect way more movement if there was no tracking at all. 



#27 Karlp295

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Posted 27 September 2020 - 10:42 AM

I am using Alt-Az with Got To as I have a Celestron 130SLT. Some frames may have slight star trailing but I glanced through them before stacking and most of them are OK. I usually zoom in and check the shape of the stars. I don't believe this is the problem, but I could upload more frames if this helps.

 

Thanks for any suggestions.

I also try to set focus on Alpheratz before going to Andromeda and I use a Bahtinove Mask for that.



#28 idclimber

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Posted 27 September 2020 - 02:42 PM

The most important component in an astrophotography rig is the mount. The Alt-Az mount you have is simply not up to the task of holding the sensor steady within one pixel for one minute or longer. The data may be there but it is smeared across the sensor.



#29 GoldSpider

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Posted 27 September 2020 - 05:28 PM

Like others are saying, alt-az and long-exposure DSO astrophotography is a short road to a dead end.  An alt-az mount is serviceable for shorter exposure work like EAA, but the software to run that is typically made for purpose-built astro cameras. 

 

If you're not looking to purchase anything, I'd recommend taking wide-field shots with a tripod and lens.  You can learn a lot about image capture and processing, as well as how to use calibration frames, before spending money on an equatorial mount.



#30 Karlp295

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Posted 28 September 2020 - 03:14 AM

Many have taken good astrophotos with Alt Az, I know it is not ideal. If the problem is the mount then why do I get good pictures from other targets such as M33 and M27? I don't believe it is the mount that is affecting this picture. I am only trying 30 seconds now and the target is in the East where star trailing should be at a minimum.

 

I will post pictures of other targets I have taken.

 

Thanks!



#31 Karlp295

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Posted 28 September 2020 - 03:21 AM

M33siril

 

M33 Stacked in Siril from 60 second exposures. With CLS filter.


Edited by Karlp295, 28 September 2020 - 03:50 AM.


#32 Tapio

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Posted 28 September 2020 - 04:49 AM

That looks good in detail but not so in colour.

Is it binned  ?



#33 Karlp295

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Posted 28 September 2020 - 06:07 AM

Yes. I am still learning how to post process. I just wanted to show that I am getting some detail and confused why the detail is limited for Andromeda.

 

I will post more pictures later.



#34 RJF-Astro

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Posted 28 September 2020 - 07:30 AM

Well the thing is AP is complex. So there are those who have succes with an alt/az mount. But more often they do not. And when things go wrong, it gets more complicated to determine the issues and solve them. That is why the general advice is to start off easy, with an adequate EQ mount and a small refractor.

If you are set on using the alt/az, be prepared to do more troubleshooting and spend clear sky time solving issues and getting to know your gear.

In any case, imo tracking performance needs to be evaluated. I do not have experience with alt/az tracking, so I cannot help there. But I do not think your answer lies in post processing.

#35 GoldSpider

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Posted 28 September 2020 - 08:14 AM

Most of the light frames you posted show some fairly significant tracking issues to the extent I'm not sure DeepSkyStacker will recognize the stars.  Color-wise, the lights and darks look fairly neutral, so for now I suspect Siril is doing something weird to send the color balance way out of whack.

 

I'd be able to tell you more if I had some better light frames to work with, but I understand that access to online storage isn't always an option.



#36 Karlp295

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Posted 29 September 2020 - 01:44 AM

Hi Goldspider. I am curious about the tracking errors, what exactly do you mean by that?

 

I am trying to take shorter exposures to avoid star trails or movement in the image. Some may have been caused by wind, as it is fairly windy here although i am imaging very close in shelter next to my house.

 

I also check most of the pictures after they are taken to see the shape of stars etc. They looked OK.

I am trying to focus as best I can on Alpheratz first with a batinov mask.

 

Maybe the light frames you saw were not good ones but I took many and only uploaded the first five.

 

Thanks and appreciate any advice. The EQ mount will come later, or I will construct something.



#37 GoldSpider

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Posted 29 September 2020 - 07:59 AM

Hi Goldspider. I am curious about the tracking errors, what exactly do you mean by that?

 

I am trying to take shorter exposures to avoid star trails or movement in the image. Some may have been caused by wind, as it is fairly windy here although i am imaging very close in shelter next to my house.

 

I also check most of the pictures after they are taken to see the shape of stars etc. They looked OK.

I am trying to focus as best I can on Alpheratz first with a batinov mask.

 

Maybe the light frames you saw were not good ones but I took many and only uploaded the first five.

 

Thanks and appreciate any advice. The EQ mount will come later, or I will construct something.

Things like elongated stars or "jagged" stars where wind affected an exposure.  All of the light frames you linked to had some problem with the stars.  If you could ZIP up all of your data (lights, calibration frames) and make them available somewhere, that would help enormously in troubleshooting.



#38 venyix

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Posted 29 September 2020 - 08:42 AM

I have a used StarAdventurer Pro that I would be willing to sell, it’s a great place to start and learn about tracking. I tried using an Alt/Az mount for imaging and got so frustrated I gave up. I use an EQ6R Pro now and I’m in love with it.



#39 Karlp295

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Posted 29 September 2020 - 12:02 PM

Venyix I would love to get that depending on price of course. The problem is I am in Turkey now and unable to get back to the UK for the time being. Where are you? Would that be suitable for a telescope such as my Celestron 130slt?

 

Sending it would probably be a big problem.



#40 idclimber

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Posted 29 September 2020 - 01:47 PM

The StarAdventure Pro is a camera tracker designed for DSLR cameras and lenses. They are great with medium length lenses (50-200) or something like a Redcat at 200mm. That mount is really not designed or suitable for a 6" newt with a 1200mm focal length. Too much weight and too much focal length. 

 

Your photo of M33 is consistent with images produced in EAA with these mounts. The only way you are going to get your individual lights to have nice tight round stars with your mount is to decrease exposure time until they are round. This might mean you need to be shooting at less than one second. Then you are forced to crank the ASA up to the point that the noise will simply overwhelm any signal you may have. If you can't upgrade your mount at this time, I think you would be well served to pick up one of the cameras currently popular for EAA like the ASI224.

 

The periodic error and mechanicals of the mount mount make a huge difference in arc second pointing accuracy. A little too much backlash or a simply a gear that was machined badly and a hundred other mechanical details done poorly means it simply will not work for AP. This is really not surprising. A respectable mount for this size scope is easily three times the cost of that package. Your scope and mount were primarily designed around price and to use visually.

 

Something else that will affect how accurately your mount points is how well you do your star alignment. When I wanted my LX200 to point well, I used an eyepiece with a lighted reticule during that alignment. Even then I would sometimes have to repeat that alignment a few times. A tedious and annoying job at best, at least it was for me. 

 

Then there are other issues like focus, collimation, and coma that all have to be solved. Perhaps you have most of these items addressed as you stated, but the proof is in the lights and I don't simply don't see it in yours. I am sorry if I am being overly blunt.

 

I am not sure you are aware of this, but there are differences in apparent motion of the stars including rotation based on where in the sky you are pointing. This can be used to increase exposure time without star trailing. There are threads you can find here on the topic. 

 

If you are stacking the lights that I inspected, your integration will simply not have the fine detail you are asking for. When I am integrating my lights I toss out the worst 20-30% and I apply a weighed average to stack what is left. You need to toss every light with noticeable star trails. This means you need to inspect them at a pixel level scale or use software that can do that for you. Averaging the poor subs will only degrade your end result. 


Edited by idclimber, 29 September 2020 - 01:57 PM.


#41 Karlp295

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Posted 30 September 2020 - 04:02 AM

Thanks for all the advice. I am shooting towards the east where the max exposure should be without trailing. I suspect the problem might be with the mount but for the time being I am trying my best with it. I have got some decent results so far.



#42 venyix

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Posted 04 October 2020 - 01:55 AM

My mistake, I didn't realize you were using a large reflector. The StarAdventurer definitely wouldn't work well for that size scope. However, I think if you already have a telephoto lens (or a lens with a decent enough focal length), you would probably get much better results with the StarAdventurer + Lens + Canon than with the reflector + Alt/Az. I've gotten some really great images using the StarAdventurer and the Rokinon 135mm F2. As seen below.

pinwheel
The Andromeda Galaxy


#43 Karlp295

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Posted 11 October 2020 - 01:17 PM

I'm just wondering as I have continued to image without the CLS filter, if different exposures are necessary for the dust lanes around the core. I have imaged so far with 30 second exposures at ISO 800 on my unmodded Canon 600D.

 

I am now taking some subs at 60 seconds. With alt-az mount I may not be able to go much above this but 90 seconds could be possible when it is in the east.

 

Will this make a difference if I mix exposures together?




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