Star trails , star trails.....

[OJ87]

Hi everyone, 

Last night I started imaging, I took about 30 * 120sec . 

I tried it without Autoguiding, because my laptop didn't want to wake up 😞. 

Some of photos were awesome, others were with beginning trails, other with terrible trails. All of them were mixed, I mean after a good shot I got a very bad one and so on... If it was bad polar alignment I wouldn't get any good shots, if it was good , then why I'm getting the bad one? Any ideas why would that come from?

Best regards, 

[david_taurus83]

Was it windy by any chance? That's a big scope you've got in your signature. At that focal length you'll really want good polar alignment and good guiding.

[OJ87]

40 minutes ago, david_taurus83 said:

Was it windy by any chance? That's a big scope you've got in your signature. At that focal length you'll really want good polar alignment and good guiding.

Hi David, 

No it was a still night. No wind at all. 

Polar aligning was with eyeballing, it wasn't perfect. But if it was bad, how I got that good images? Good images rate was 1:3. 

[david_taurus83]

Was everything balanced  in the mount? I don't know the answer. Like I said, at 1000mm focal length, you really want good guiding. I was shooting at 570mm last week with essentially the same mount, good guiding and I still got slightly eccentric stars. Tbh, if you got around 30% good images without guiding, that's pretty good. Keep them and try to get guiding sorted for the next night.

[JamesF]

Posting an example of some of the trails might help?

James

[OJ87]

HI David, 

Hmm, it may be a balance problem. I balanced it with the 2" eyepiece , then replaced them with the camera, but didn't checked the balance 😕. The weight difference wasn't that big

 

Edited May 26, 2019 by OJ87

[OJ87]

9 minutes ago, JamesF said:

Posting an example of some of the trails might help?

James

Hi James,

sure. Here some of them, I will attach  them as stock , not edited. Some of them are good results as a reference. 

Best regards, 

 

[JamesF]

Is it my imagination, or is the direction of the trail changing over the last three images?

James

[OJ87]

1 minute ago, JamesF said:

Is it my imagination, or is the direction of the trail changing over the last three images?

James

You are right, I didn’t notice it, how could it happen? 

[JamesF]

I'm trying to work that out as well

James

[happy-kat]

There are two that look like stiction jerk as the trail is broken. Did a trailing cable get tight.

[OJ87]

49 minutes ago, happy-kat said:

There are two that look like stiction jerk as the trail is broken. Did a trailing cable get tight.

Hi Happy, 

the cable wasn’t tight at all.

[ebdons]

Hi, not sure on your mount but my EQ6 pro sometimes gives me that error when the balance is wrong or the clutches are not tight enough, and also I reverse the direction one way or another until it stabilises the image? not saying that you may have done this already? ton

[david_taurus83]

Whatever it is it's a sudden movement as the inner trail is narrower than the actual star. I still think it could be a breeze.

[michael8554]

The dumbell shaped stars are due to backlash. The mount has spent some of the 120 secs at one end of its backlash,  then flopped  to the other end, giving two stars joined by a trail.

On some shots this hasn't happened, so balance must be right on the edge.

Could also be Periodic Error, with the good shots coinciding with the PE peaks where RA change is least, but I prefer Backlash as the cause.

Balance slightly heavy in one direction.

Michael 

[OJ87]

12 hours ago, michael8554 said:

The dumbell shaped stars are due to backlash. The mount has spent some of the 120 secs at one end of its backlash,  then flopped  to the other end, giving two stars joined by a trail.

On some shots this hasn't happened, so balance must be right on the edge.

Could also be Periodic Error, with the good shots coinciding with the PE peaks where RA change is least, but I prefer Backlash as the cause.

Balance slightly heavy in one direction.

Michael 

Thanks Michael, 

but does backlash comes so frequently? I have such lines approximately in every 10min. 

Does also backlash explain the reversed directions of the stars?

 

[OJ87]

13 hours ago, ebdons said:

Hi, not sure on your mount but my EQ6 pro sometimes gives me that error when the balance is wrong or the clutches are not tight enough, and also I reverse the direction one way or another until it stabilises the image? not saying that you may have done this already? ton

Hi ton,

I'm sorry, but I didn't get what did you mean by (reversing the direction till image stabilisation)? Could clear it for me?

Thank you

[geordie85]

5 hours ago, OJ87 said:

Thanks Michael, 

but does backlash comes so frequently? I have such lines approximately in every 10min. 

Does also backlash explain the reversed directions of the stars?

 

I believe it takes around 8 minutes for the gears to do 1 full cycle so that sounds about right. 

[ebdons]

Hi, it maybe backlash, when I reverse the direction of the mount to opposite to where the star trails are going, I have a 8" newt and an SCT 8" side by side and have to rebalance it very well to compensate when imaging near the horizon. it works like this, watch the stars as they are imaged and use the mount motors to go against the direction of trail until they have stabilised and they seem to be more steady, but my EQ6 may be on the limit of it's capacity with my setup?, I don't know if the motors are being forced to tighten up or something else. my eq6 pro has the belt mod and extended weight bar which I found is a positive. but lots can make the stars trail as folks have said, wind, flexture etc. it may help or not.

[bobro]

The Quattro 10S is quite a heavy OTA (although within the stated capacity of the EQ6-R) so will tax the mount to some degree. Perfect OTA balance isn't always a good thing, especially with a heavy load. When I started with imaging I had a reflector on an (overloaded with extension bar) EQ2 mount and would see similar images to yours if the setup had not been adjusted to be east heavy. I tried west heavy but is didn't work. If the setup is near perfect balance it can stutter in RA, producing images such as yours. When east heavy the motors keep pushing the scope in RA and provide smoother movement. Not really connected to periodic error - just a question of taking up the mechanical slack/backlash.

The good news of course is the image you posted with no trailing - a sign of great things to come!

[dph1nm]

On 27/05/2019 at 11:18, geordie85 said:

I have such lines approximately in every 10min.

In which case it looks like classic periodic error to me. The image scale is sub-arcsecond per pixel - getting untrailed images in 120sec at that scale with an unguided EQ6 would be a pretty impressive feat.

NigelM