AZ-EQ6 GT Tracking Problems

[c3dr1c]

Hi everyone.

I'm from Portugal and I'm coming here to try to find some help and advises from your community about my telescope mount.

Could you please give-me your opinion about the following report? In case you have the same telescope mount, could you please tell-me if you can do good minutes of exposure time?

Please find attached the same report in pdf file.

Thank you in advance :)

 

1.  My Experience

I already had two different telescope mounts from Skywacther: NEQ6 and AZ-EQ 6 GT.

When I received both mounts, I performed proper calibrations advised by the manufactory and also by experienced amateur astronomers:

·            Polar scope reticle alignment;

·            Level and mark zeros on both axis;

·            Mark the polar scope position to place the 0h on the top and 6h on the bottom, more vertical as possible.

·            Use a good level to level the tripod instead of the bubble of the mount.

·            Worm adjustment.

·            Etc…

With both previous mounts, with a newton telescope with 1200mm of focal length and with a Canon 600D (aps-c sensor – 1.6x crop factor), I easily taken photos with 2 minutes and half of exposure time (without autoguiding system).

I can check some of my work at: www.cedricpereira.space

 

2.  Current Equipment

I sold all my previous equipment and after two years, I decided to buy the same equipment again.

So, when I received my telescope mount, I did all the calibration again! And after 2 months, due to covid pandemic, I was free to test it.

I did all the tests with the same equipment as before, a newton telescope 254/1200mm and a Canon 600D. But now, the results are quite strange. I can’t do 1 minute exposure time without star trails. Even with 30 seconds I can see some trails. Look at the following images.

 

30 seconds exposure time:

As you can see there is a small trail. It could be from the wind, but even when I do multiple photos, I have always the same trails. The telescope is well collimated and as you can see, I’m analyzing the central part of the image (to avoid aberrations, as coma). It could also be the cameras’ shutter inducing some vibrations on the telescope, but I checked if it happens in the “live view” mode (open shutter), and yes, it happens.

  

Now let me show you a “crop magnified view” from two consecutive images with 30 seconds of exposure time:

  

Time to time the problem doesn’t happen, as you can see on the first image. But on 95% percent of my photos I see small trails, as you can see on the second image.

 

Now, a 2 minutes exposure time image:

After the first tests, I decided to go home and do all the calibrations again. I also checked the power voltage of my power supplies and I performed a worm adjustment for both axis to almost eliminate the “backlash”. To finish, I updated the firmware of the remote control and of the motors.

Regarding the firmware update I noticed something strange. After the update, the noise of the telescope mount while slew is quite strange! I think it’s not normal.

I went to a dark place again to try to check if the mount could track stars properly. But I got the same results! Photos of 30 seconds of exposure time with star trails.

 

30 seconds exposure time:

 

 2 minutes exposure time:

V shape trail?

So, I decided to take longer photos to try to understand what is happening. Have a look on the following images:

5 minutes exposure time:

 

10 minutes exposure time:

 

20 minutes exposure time:

 

30 minutes exposure time:

 

I got a good polar alignment error of just few arc seconds, I tested without wind, I checked if the behavior is the same with a battery or a wall power supply, I checked if it does trails pointing to the zenith and/or to the horizon. I don’t know what to do more.

Thank you.

 

az_eq6_report.pdf

[c3dr1c]

I sent the mount to the manufacturer to check and correct possible issues.

This week I received the mount and yesterday I performed some tests. I got the same problems...

I did one photo with 5minutes exposure time (of course I'm not expecting point stars with such exposure time).... just to check the behaviour:

It looks like the telescope mount is somehow oscillating...

[Dr_Ju_ju]

One observation, levelling the mount tripod doesn't matter as long as you have good polar alignment, also is all you gear properly balanced ?? 

[Adam J]

You may need to adjust the gear mesh, a PHD guiding graph would be very helpful to diagnose this. The last image you posted looks like something is binding. Could be anything from cable drag, to a cluch problem, to backlash, binding gears. Everything can be adjusted mind you.

Adam

Edited October 11, 2020 by Adam J

[c3dr1c]

Thank you so much for your help. I will try to use Sharpcap to get a precise polar alignment and also to use PHD2 to get information from the guiding graph!

Let's see what happens!

I would like to know if this is a common problem for such focal distance/field of view.

The quality of the mounts seems to be worst than some years ago, at least from Synta... I'm so sad with this...

[vlaiv]

You are not guiding and this is to be expected - it is combination of polar alignment error and periodic error.

Every mount has it to some extent and this is the reason why people guide - to eliminate the two.

Look at that line in 20 minute image. It has smooth component in one direction and it has oscillatory component in perpendicular direction.

If you check your images, you'll find that smooth component is in DEC direction - that is drift due to polar alignment error. You will also find that perpendicular to that - what is causing "waves" is RA direction and cause of those waves is periodic error - which is due to fact that gears are not perfect circles.

Look at the same thing happening as a movie:

Either start to autoguide or check your mount manual for something called PEC - which is periodic error correction and try to see how much it will help. For better polar alignment - look at drift method.

 

[david_taurus83]

At 1200mm focal length, guiding is a must on a Skywatcher mount. I would even say off axis guiding for this.

[wimvb]

My experience with the AZ-EQ6:

you need to remove backlash, which in itself doesn’t improve tracking, but it will improve guiding.

you need to tighten the ra belt. If not, you will get a 10 s periodic wiggle. This can not be guided out easily.

you will then have a 120s periodic error which corresponds to one rotation of the ra timing pulley. This is smooth and can be guided out.

you need perfect polar alignment if you don’t guide. If not, your images will exhibit so called walking noise.

the mount has permanent periodic error correction, which you need to program, unless you guide.

Best practice with this mount: you need to guide it.

edit: to make analysis easier, rotate the camera such that the sensor’s long edge is aligned to RA.

Edited October 17, 2020 by wimvb

[c3dr1c]

Hey guys!

Thank so so much for your help! It's very good to check the opinion from others.  

I understand your opinion about my telescope mount and that I have a big focal length, but In the past, with the same equipment I was able to achieve 2 minutes and half of exposure time without star trails! I bought this new mount due to that reason! It cost more than 1500€! Why I should now accept this lack of quality from Synta. I think it's really bad to allow Synta to lower the quality of their products!

Actually I ask some friend and they can achieve 1 minute and half easily with similar equipment. Maybe I'm wrong, but this is my honest opinion.

It looks like since Skywatcher introduced this green fancy color on their products, everything is worst 😛 

 

Anyway, yesterday I performed more tests  

 

1.  Intro

As you can read on my first report about the SW AZ-EQ 6, I have had tracking problems with my telescope mount. After the first report, I sent the telescope mount to the supplier, for them to review and correct possible issues.

After about one month, I received my telescope mount. Again, I performed proper calibrations advised by the manufacturer and also by experienced amateur astronomers. I notice that the strange slew noises that I reported on the last report, have disappeared. But after some tests, the tracking issues still remain:

30 seconds of exposure time:

So, I decided to go home and study a new away to improve my tests!

 

2.  New Tests!

At home, I have been in contact with some national and international communities of astronomers to get some advices about what I have to do. According with them, I should try to improve my polar alignment using SharpCap (a software that can be used for that purpose) and also get some plots from PHD2 Guiding (another software to auto-guide my mount and to check for tracking issues).

After studying everything, I went back to the field for some tests.

 

First, I did the traditional polar alignment as I’m used to. I got a good misalignment error:

 

Then I decided to acquire some exposures to check again the behavior of my telescope mount. From many photos, 90% of them have trails. Time to time, there is a photo without trails.

Two consecutive pictures of 60 seconds (one without trails, another with trails):

The behavior is still the same!

 

So now it’s time to use a software to check my polar alignment.

According with SharpCap, my polar alignment was good:

 

But it can be improved. So, I corrected the misalignment in order to get an excellent accuracy:

 

After that, I did more exposures and I still have trails on my photos.

30 seconds of exposure time:

60 seconds of exposure time:

90 seconds of exposure time:

 

Finally, I connected the telescope mount to a computer to use PHD2 to diagnose problems.

First, I activated an option in PHD2 to correct any displacement of the target star from the center of the field of view (auto-guiding). On the following plot you can check the RA axis (in blue) and DEC axis (in red). Time to time there is a big correction on the RA axis (in yellow):

 

The following plot has the performed correction and the axis variation over almost 30 minutes of tracking (auto-guiding):

 

Then I turned off the auto-guiding option, just to check the behavior of the axes. The telescope mount is tracking, but without the aid of PHD2.

The following plot has the target star variation on the field of view, over almost 20 minutes:

Since Earth’s rotation speed is constant, I expected to get a constant motion of my RA axis. Of course, the gears are not 100% perfect, but in my opinion, the gears or the electronics of this telescope mount are not working well.

 

3.  Opinions from other communities:

I have been in touch with some national and international communities of astronomers. They agree with me: there is a problem in my telescope mount.

As I said in my first report, I easily achieved 2 minutes and half of exposure time without trails, with my last two telescope mounts (NEQ6 Pro and AZ-EQ6 GT). With this new mount, even with 30 seconds, I can detect some trails.

Some other astronomers confirmed to me, that with a similar equipment, they can easily achieve 1 minute and half of exposure time without trails!

I hope this can help.

Thank you.

Edited October 19, 2020 by c3dr1c

[vlaiv]

Hi @c3dr1c

What I'm seeing is just regular SkyWatcher sample to sample variation and periodic error in line with most mounts of that class. Periodic error seems to be around 20" or so P2P.

As I see it - you can return the mount and try another one in that class - but there is no guarantee that you won't get similar issues (some mounts are fine, and some are like one you have now). Other option is to tune the mount yourself. Of course, there is third option - stretch your budget and get better mount.

I also had issues with my HEQ5 mount. Like you - I had very bad spike in RA that repeated regularly and it had more than 5" amplitude. It was due to broken housing on one of the bearings:

So I stripped down my mount and replaced all the bearings and replaced grease and tightened properly everything. I also did a belt mod (you don't have to that on your mount since you already have belt transmission).

Here is an example of PE analysis that I did at some point:

You will see that I had something like 46" P2P periodic error prior to belt mod.

 

[c3dr1c]

Thank you for your help

New updates...

RA axis:

Example of metal filings found:

I switched the RA axis with DEC axis...

Next week I will perform new tests

Edited October 30, 2020 by c3dr1c

[Marcelo]

On 30/10/2020 at 20:47, c3dr1c said:

Thank you for your help

New updates...

RA axis:

Example of metal filings found:

I switched the RA axis with DEC axis...

Next week I will perform new tests

Did it work?

[c3dr1c]

Hello everyone!

After a few months, today I did the first tests after disassembling my mount, cleaning everything and replacing the RA axis with the DEC axis.

And now, 2 minutes of exposure time without guiding!!!!!!!!! 😀😀😀

 

I'm happy! The stars are almost round! Sometimes they are a little bit oval, but much better if you compare with my results for 30s!!

I have to do more tests in a good quality night sky. I will complete my report after the new tests.

 

Cheers, 

Cédric

Edited March 19, 2021 by c3dr1c

[Fedele]

The prices of Sw and Synta have generally risen and will experience large increases.
This in the face of qualitative uncertainty that perhaps will increase in the coming months due to the covid?
At this point it is better to focus on Vixen or other quality products