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#1 Order_66

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Posted 28 February 2020 - 10:26 AM

Hello brain trust!

 

I know you guys can help me here!

 

my setup:

iOptron skyguider Pro

WO z61 APO

Canon t6 with adapter for z61

Polar aligned as best that i could

I am using the DEC bracket with counterweight

scope is connected directly to DEC bracket with provided parts the skyguider

 

i took 30 pictures at 2 minutes each.  I would expect all the pictures to be very similar.  But what i have is one picture will be pretty in focus and tracking and the very next one will have star trailing and the one after that could be back to clear and tracking.  The object in frame moves around in the photos both up and down or left and right.  Not much but enough to notice when scrolling through the pictures

 

My set up had my camera on the left with my counterweight on the right and it was balanced before i locked it down.

 

Any thoughts on changes to my set up to help?  Do i need to add a bit more balance to the weight side to help pull the camera and scope upward?

 

Thanks

 


Edited by Order_66, 28 February 2020 - 10:27 AM.


#2 Order_66

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Posted 28 February 2020 - 10:28 AM

Here is the trailing Picture

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  • Trailing.png

Edited by Order_66, 28 February 2020 - 10:29 AM.


#3 Order_66

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Posted 28 February 2020 - 10:29 AM

Here is the Not trailing

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  • Not Trailing.png


#4 DubbelDerp

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Posted 28 February 2020 - 10:39 AM

That's how mine behaves - 2 minutes is long enough to show the periodic error of the tracker. At 360mm focal length, my maximum exposure is 60 seconds and I still see the periodic error, although within my acceptable limits. I think you're just pushing the little mount too hard.



#5 Order_66

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Posted 28 February 2020 - 10:49 AM

That's how mine behaves - 2 minutes is long enough to show the periodic error of the tracker. At 360mm focal length, my maximum exposure is 60 seconds and I still see the periodic error, although within my acceptable limits. I think you're just pushing the little mount too hard.

I was thinking the same thing.  Was planning on moving back to 60 second exposures tonight if the sky is clear.  Thanks



#6 the Elf

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Posted 28 February 2020 - 10:50 AM

Assuming the PE is roughly sinusoidal you have little trailing at the curves mins and maxs but strong trailing at the slopes. You basically have to accept a loss rate unless your exposures are very short. For this target you can easily go for 30 sec exposures.


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#7 Cfreerksen

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Posted 28 February 2020 - 11:16 AM

Hello brain trust!

 

I know you guys can help me here!

 

my setup:

iOptron skyguider Pro

WO z61 APO

Canon t6 with adapter for z61

Polar aligned as best that i could

I am using the DEC bracket with counterweight

scope is connected directly to DEC bracket with provided parts the skyguider

 

i took 30 pictures at 2 minutes each.  I would expect all the pictures to be very similar.  But what i have is one picture will be pretty in focus and tracking and the very next one will have star trailing and the one after that could be back to clear and tracking.  The object in frame moves around in the photos both up and down or left and right.  Not much but enough to notice when scrolling through the pictures

 

My set up had my camera on the left with my counterweight on the right and it was balanced before i locked it down.

 

Any thoughts on changes to my set up to help?  Do i need to add a bit more balance to the weight side to help pull the camera and scope upward?

 

Thanks

You can guide the SGP. Makes a world of difference for long exposures.

 

Chris



#8 sg6

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Posted 28 February 2020 - 12:14 PM

120 seconds is likely too long for the mount. It is considered too long for a decent Eq mount and the Skyguider is a lot smaller and likely will "fail" earlier.

 

Try 40 or maybe as high as 60 seconds, but no longer.

 

There is something about that "trailing" as it looks like a small skip/jump. Makes me wonder if there is something else going on to cause it.

 

What Wait time do you have between exposures?


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#9 scadvice

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Posted 28 February 2020 - 12:15 PM

Take in consideration where you are guiding in the sky.  As you get farther from the Polar Center the objects are moving a longer distance over the angle.  Think of a fan. So your polar alignment needs to be more accurate as you go South. So does mechanical and atmospheric correction to avoid drift.

 

Another way to think of it is in the Northern Hemisphere the farther South you are the greater your tracking accuracy needs to be. If you can't correct your drift then reduce the exposure time so that less error appears on the image. 

 

Using my iOptron SkyGuider, I just did Witch Head with exposures at 90 sec each using a WhiteCat 51mm  F/4.9. That was the best I could do unguided and still keep round stars with the Tracker and I'm using the PoleMaster off my large setup to align.

 

I'm in agreement with those above shorten your exposures with the brighter objects and just take more images.

 

Other thoughts: With the inconsistent frames something may be loose. Next, I believe the blurring or 'out of focus' as you called it comes from the star trailing movement which makes the image look to be out of focus.  


Edited by scadvice, 28 February 2020 - 12:25 PM.

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#10 Order_66

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Posted 28 February 2020 - 04:11 PM

You can guide the SGP. Makes a world of difference for long exposures.

 

Chris

Do you mean get a scope and camera and auto guide?  I was thinking about that too.



#11 Cfreerksen

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Posted 28 February 2020 - 07:13 PM

Yes just get a small zwo scope and a cheap guide camera with ST-4 output.

Chris

#12 the Elf

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Posted 29 February 2020 - 03:29 AM

AP is like many real life processes: a lot of things are far from optimal but one of them is the biggest problem. Big enough to cover the other problems. As soon as you solve it, the second biggest problem is your new number one. As Elfs can foresee the future I can tell you what is next. The guider solves the periodic error problem so that you can go for longer exposure times. Now polar alignment is your new number one problem. If it is absolutely perfect you can shoot long subs. If not you have star trails caused by polar misalignment. If you have a mount with two motorized and guided axes the guider solves both problems. Even a mediocre polar align works for reasonable long exposures. As your tracker has got only one axis you can't solve that. You can spend a lot of time for good polar alignment using the method of drift alignment by the German astronomer Scheiner. If you want to go deeper in this hobby you will sooner or later want to have two axes.

 

As the guider will work with any mount you can get one, use it with the skyguider and think about a mount later. This mount is probably on the same load and quality level as the skyguider. Maybe you can sell the skyguider and get it for little extra cost:

https://www.amazon.c...e/dp/B00B9JPIO4

 

The load capacity and accuracy is not any better. If you want to update for a large telescope one day think about 3 times the price.

Here is a video by Nico Carver about this mount:

https://www.youtube....h?v=Qb1ceFM-DkQ

(Thank you so much Nico! I love this video.)


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#13 Order_66

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Posted 29 February 2020 - 02:03 PM

120 seconds is likely too long for the mount. It is considered too long for a decent Eq mount and the Skyguider is a lot smaller and likely will "fail" earlier.

Try 40 or maybe as high as 60 seconds, but no longer.

There is something about that "trailing" as it looks like a small skip/jump. Makes me wonder if there is something else going on to cause it.

What Wait time do you have between exposures?


10 seconds

Edited by Order_66, 29 February 2020 - 02:04 PM.


#14 scadvice

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Posted 29 February 2020 - 03:18 PM

With good alignment, a stable tripod, and balance you can get good and consistent images. Those three things are very important. People tend to use too light of tripod, not balance carefully and only 'sort of' get polar alignment in.

 

Yes, the wider the field and closer to the polar star you are and the more error you can get away with but if you want to go long on an exposure then you need to pay attention to details.

 

This is 70 sec each frame totaling 67 frames unguided with a iOptron SkyGuider Pro, WO WhiteCat 51mm F/4.9 using an old T3i DSLR camera at 800 ISO with BackyardESO. This a full frame image.

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  • M42HH_reduced.jpg

Edited by scadvice, 29 February 2020 - 03:35 PM.

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#15 Cfreerksen

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Posted 01 March 2020 - 02:36 PM

Some lovely images can be had with the SGP if you do short exposures. At your focal length I would stay at 60 seconds or below.

 

This is with a rig similar to yours. Z61 and Canon RP. 60 second exposures.

 

Chris

 

 

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  • OrionPlusColorCorRED.jpg

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