First night out with the EQ6 - R Pro (Star trail diagnosis)

[Iem1]

Hey Guys,

Absouletly delighted to have spent a few hours outside with my EQ6 - R Pro for the first time. Been sat waiting over 2 months for a battery pack to be able to use it. Thoroughly enjoyed learning how to use GoTo and Synscan controller functions, first time ever using GoTo of any kind (Prior 6+ months with a Sky Guider Pro).

I THINK I left last night having got the hang of everything, after spending around 1.5 - 2 hours learning/tweaking stuff, but I just wanted some feedback regarding my first attempt at setting up. There were star trails in 60/30 and even a bit in 15 second subs. I came to the conclusion that the setup was not balanced properly, but If anyone can identify that would be amazing so I know what I am looking at;

60 second sub

 

30 second sub

 

After starting from scratch again and being very careful with balancing, a 30 second looked like this;

 

For PA, I pointed the setup north, balanced the gear, then set home position, turned it on and did 3 star alignment (Pretty accurate, I could GoTo Whirlpool galaxy and Rosette nebula without issue) and then I used the hand controller to do PA, where you center a star and then it moves and you recenter with the Altitude bolts and Azimuth bolts (Drift Alignment?), and both were below 10 arcseconds after PA I believe it said.

- When setting N Coords, I needed to input something like 51.93 but it would not let me progress with this number, I had to use N 52.00 for some reason? Do not think it made too much of a difference though.

But does the trail look like it was caused because the setup was not balanced fully? (Not guiding btw)

[Stuart1971]

1 hour ago, Iem1 said:

Hey Guys,

Absouletly delighted to have spent a few hours outside with my EQ6 - R Pro for the first time. Been sat waiting over 2 months for a battery pack to be able to use it. Thoroughly enjoyed learning how to use GoTo and Synscan controller functions, first time ever using GoTo of any kind (Prior 6+ months with a Sky Guider Pro).

I THINK I left last night having got the hang of everything, after spending around 1.5 - 2 hours learning/tweaking stuff, but I just wanted some feedback regarding my first attempt at setting up. There were star trails in 60/30 and even a bit in 15 second subs. I came to the conclusion that the setup was not balanced properly, but If anyone can identify that would be amazing so I know what I am looking at;

60 second sub

 

30 second sub

 

After starting from scratch again and being very careful with balancing, a 30 second looked like this;

 

For PA, I pointed the setup north, balanced the gear, then set home position, turned it on and did 3 star alignment (Pretty accurate, I could GoTo Whirlpool galaxy and Rosette nebula without issue) and then I used the hand controller to do PA, where you center a star and then it moves and you recenter with the Altitude bolts and Azimuth bolts (Drift Alignment?), and both were below 10 arcseconds after PA I believe it said.

- When setting N Coords, I needed to input something like 51.93 but it would not let me progress with this number, I had to use N 52.00 for some reason? Do not think it made too much of a difference though.

But does the trail look like it was caused because the setup was not balanced fully? (Not guiding btw)

Hmmm, if it was below 10 arc seconds, you should get over 5 min subs with no trailing on that scope, I would think it was more like under 10 arc minutes…

As long as balance is gold it should not trail, it’s down to PA…👍🏼

My PA is under 3 arc mins, and I can get around 6 mins unguided with no trails due to alignment, but periodic error will also play a big part in star shapes…so good PA and good guiding is what you need…..👍🏼

Edited March 19, 2022 by Stuart1971

[Iem1]

1 hour ago, Stuart1971 said:

Hmmm, if it was below 10 arc seconds, you should get over 5 min subs with no trailing on that scope, I would think it was more like under 10 arc minutes…

As long as balance is gold it should not trail, it’s down to PA…👍🏼

My PA is under 3 arc mins, and I can get around 6 mins unguided with no trails due to alignment, but periodic error will also play a big part in star shapes…so good PA and good guiding is what you need…..👍🏼

Oh maybe it was minutes! Still learning the how to read/use the Synscan 

At one point one of them was just 0, which I thought HAD to be wrong because the chances of me getting a perfect alt/az alignment is surely pretty slim...might have actually messed up one of the star alignments (wide field of view!) And perhaps that was throwing it off or something.

couple more clear nights ahead so looking forward to testing it out again!

[vlaiv]

Looking at your images and camera orientation - I think that main culprit for star trailing is not polar alignment but rather periodic error of the mount.

From first image I conclude that you tried to orient your FOV so that DEC is up/down on sensor and RA is left/right. Not sure how accurate you tried to do that, but if you look at your trailing - it is mostly in left/right direction - which would mean it is in RA and that means - periodic error.

Polar alignment error creates trailing in DEC, while periodic error creates trailing in RA.

You really need to take about 8 minutes of consecutive 30s subs to get the idea of how your periodic error behaves (I think EQ6 mount has worm period of about 480s give or take - that is 8 minutes). Some of those subs will have trailing, others won't because periodic error is not uniform in nature.

What you think is due to better balance - could as well be due to "calm" part of periodic error curve.

[Iem1]

51 minutes ago, vlaiv said:

Looking at your images and camera orientation - I think that main culprit for star trailing is not polar alignment but rather periodic error of the mount.

From first image I conclude that you tried to orient your FOV so that DEC is up/down on sensor and RA is left/right. Not sure how accurate you tried to do that, but if you look at your trailing - it is mostly in left/right direction - which would mean it is in RA and that means - periodic error.

Polar alignment error creates trailing in DEC, while periodic error creates trailing in RA.

You really need to take about 8 minutes of consecutive 30s subs to get the idea of how your periodic error behaves (I think EQ6 mount has worm period of about 480s give or take - that is 8 minutes). Some of those subs will have trailing, others won't because periodic error is not uniform in nature.

What you think is due to better balance - could as well be due to "calm" part of periodic error curve.

Thank you Vlaiv, your input is invaluable, as ever

that actually makes more sense, when I first saw the trail I thought it looked more akin to the trail on my Sky Guider pro when it had been knocked during imaging or when I left the manual dither too late and the system was still ever so slightly wobbling as the imaging started. But I dismissed that as it hadn't been knocked/dithered, but I did not think of periodic error! 

heading back out in a few hours, going to see how accurate I can get the PA on the hand controller. Haven't actually calibrated my Polar scope yet as I wanted to use drift alignment, really liking it so far!

Hopefully il manage more than 6 minutes of test data tonight now I kind of know what I am doing

[SamAndrew]

That 30s sub looks fine to me. If you're not going to guide then I would just stick to 30s subs and throw our the bad ones; hopefully you'll get 50%+ that are useable. 

[alacant]

8 hours ago, Iem1 said:

star trails

Hi

The connection between the dovetail and the mount could be improved. Maybe consider fitting a longer plate that it be held adequately, so eliminating a source of flex.

If you don't plan to use autoguiding and have the patience, you could train the mount to reduce PE.

Cheers

Edited March 19, 2022 by alacant

[Iem1]

Thank you for all the replies guys.

Had another go tonight;

After 3 star alignment and PA, it was showing;

Mel - 000 00 ' 05 ''

Maz + 000 00 ' 00 ''

I was feeling brave and took this is 2 minute exposure

Looks much healthier! Only took x2 2 minute subs in a row, but both were pretty decent all things considered!

Took x75 1 minute subs of the NGC 869 region;

 

I am not very good at processing star clusters, need look into it. But given the near full moon and more light polluted sky I was under I thought it was a better target to try.

The untouched tif if anyone wants to look;

result.tif

 

 

Edited March 20, 2022 by Iem1

[jacko61]

I was going to comment on your vixen plate but Alacant beat me to it. - despite being a single 'edge', having only one of the clamp bolts holding the plate will mean an unstable and loose connection.   It's well known that the zs73 focus lock bolt gets in the way of the vixen sliding further back so the easiest thing would be to turn the scope upside down in the cradle so the focuser is at the top. Then you have plenty of room to move the vixen plate back so it's gripped by both of the eq6 clamp bolts - not only will you get a more secure clamp but you will be able to slide the scope further forwards to aid balance.

Graeme

[Iem1]

Hey folks, another question.

Had another outing a few days ago, long story short it did not go as smoothly as the previous session, I had trouble doing the PA. First attempt was leaving me with a small amount of trails in 60 seconds and the 30 seconds were a little inconsistent.

I read online the PA with the hand controller should be iterative, the more times you do it the more accurate it will be. However, when I try to do a second PA to improve accuracy, I select the star, the mount does its 'GoTo' and normally you are asked to center the star with the hand controller first berfore anything else, sometimes the GoTo is very accurate and it is already dead center, sometimes I need to shimmy across a little, but eitherway, upon advancing to the stage where the mount is supposed to then 'drift' away and then ask you to adjust using Alt/Az bolts in turn, it does not move? 

There is no drift at all, it simply says adjust the bolts, but of course, it is already dead center having just done the first step. The only way I can do my PA again at the moment is by switching the mount on and off, doing a fresh 3 star alignment and hoping the new PA is better.

When attempting a second PA (without starting from scratch) should I be using the same star as the first PA or selecting a star further away or something? I can not see a way to improve upon my first PA.

I will be investing in ASIair and guide cam next month, looking forward to another step up, but wanting to have the basics of GoTo nailed down first  

 

Thanks, as always.

[ONIKKINEN]

55 minutes ago, Iem1 said:

Hey folks, another question.

Had another outing a few days ago, long story short it did not go as smoothly as the previous session, I had trouble doing the PA. First attempt was leaving me with a small amount of trails in 60 seconds and the 30 seconds were a little inconsistent.

I read online the PA with the hand controller should be iterative, the more times you do it the more accurate it will be. However, when I try to do a second PA to improve accuracy, I select the star, the mount does its 'GoTo' and normally you are asked to center the star with the hand controller first berfore anything else, sometimes the GoTo is very accurate and it is already dead center, sometimes I need to shimmy across a little, but eitherway, upon advancing to the stage where the mount is supposed to then 'drift' away and then ask you to adjust using Alt/Az bolts in turn, it does not move? 

There is no drift at all, it simply says adjust the bolts, but of course, it is already dead center having just done the first step. The only way I can do my PA again at the moment is by switching the mount on and off, doing a fresh 3 star alignment and hoping the new PA is better.

When attempting a second PA (without starting from scratch) should I be using the same star as the first PA or selecting a star further away or something? I can not see a way to improve upon my first PA.

I will be investing in ASIair and guide cam next month, looking forward to another step up, but wanting to have the basics of GoTo nailed down first  

 

Thanks, as always.

Is the star trail drift in RA or DEC? Very important to know. DEC drift would be polar alignment, while RA would not. Below is a graph of my AZ-EQ6 running under guiding assistant in PHD2 with guiding disabled. This was around 15 minutes of observation. Blue is RA, red is DEC. The jittery motion is due to mechanical issues within my telescope and the way my 60mm guidescope is mounted rather than actual jittery motion of the mount itself (although some of it is probably that too).

The sharpest cliffs in blue here are happening in around 20 seconds and span across several arcseconds, so if you expose at this part of the worm, the exposure will be a guaranteed failure. Other parts are less severe and its possible you just by chance land on a part of the period where you see no issues for 60s. The worm in my mount isn't particularly good because of its aggressive features, but you could have something like this too, no way to know without measuring. This is no issue at all when guiding however, all of these are "slow" and predictable enough that guiding takes care of it completely. Maybe the sharp cliff shown here can have an extra 0.1'' RMS error during an exposure there, but its not a deal breaker.

As for the handset PA, i think you have it as good as it can be with that method. If your stars land centered each time and the mount sees no reason to adjust, it means it cant do better than you already tried.

[Iem1]

Thank you for the reply ONIKKINEN.

Now I think about it, I probably made pretty much the same mistake as I did on my first outing by the sounds of it.

Got set up, took a 60 second exposure, saw trails, immediately tried a 30 second exposure (both done within a 2 minute window), saw slight trails still, panicked and tried to fix the 'problem' thinking it was my PA this time when it was actually probably periodic error/a period of instability as you, Vlaiv and others pointed out first time around.

What I should have done is waited, took several more images of the course of 5-10 minutes to see if it had passed! Kicking myself for not thinking of this out in the field.

I think it's because I'm racing against the clock, using a DSLR, I have two batteries. An old Canon battery that lasts around 45-60 minutes out in the cold and a newer Duracell that will last ~2.5 hours. So I'm always conscious of wasting time in set up

can not wait to invest in guiding/ASIair/dedicated camera soon!

I do not think I have any of the 60 second exposures saved from that night and I did remove imperfections while going through my 30 second images, but I will see if I can find one and post it.

Thank you ONI!

 

[ONIKKINEN]

6 hours ago, Iem1 said:

 

I think it's because I'm racing against the clock, using a DSLR, I have two batteries. An old Canon battery that lasts around 45-60 minutes out in the cold and a newer Duracell that will last ~2.5 hours. So I'm always conscious of wasting time in set up

 

I know what you mean, running on camera batteries is so stressful. I had 4 old and dubious quality batteries with my 550D and if it was very cold outside that got me just 2 hours of subs, of which most were junk due to many reasons so there was always a sense of urgency with getting things going quickly.

There are dummy batteries that insert one end to the camera and the other to 12v DC or mains power if you want to run cabled and not worry about batteries. Most astro vendors have these, including FLO of course.

[Same old newbie alert]

On 19/03/2022 at 16:10, vlaiv said:

Looking at your images and camera orientation - I think that main culprit for star trailing is not polar alignment but rather periodic error of the mount.

From first image I conclude that you tried to orient your FOV so that DEC is up/down on sensor and RA is left/right. Not sure how accurate you tried to do that, but if you look at your trailing - it is mostly in left/right direction - which would mean it is in RA and that means - periodic error.

Polar alignment error creates trailing in DEC, while periodic error creates trailing in RA.

You really need to take about 8 minutes of consecutive 30s subs to get the idea of how your periodic error behaves (I think EQ6 mount has worm period of about 480s give or take - that is 8 minutes). Some of those subs will have trailing, others won't because periodic error is not uniform in nature.

What you think is due to better balance - could as well be due to "calm" part of periodic error curve.

Much that I agree with most of this I'd question that would PE show up in a 30 sec sub?

[vlaiv]

37 minutes ago, Same old newbie alert said:

Much that I agree with most of this I'd question that would PE show up in a 30 sec sub?

If you do full worm cycle at particular exposure length - it is then easy to see what percentage of subs will be affected by PE.

After capturing exposures to cover full worm cycle, you can then make something like this:

Some subs will look like this:

and some subs will look like this:

and you can count the subs and get approximate rejection rate depending on your exposure length.

If you wonder if 30s will expose PE - that depends on setup and working resolution. Just as exercise we can do 8 minute calculation of 30s at 2"/px with mount that has 15" P2P error. That is 16 exposures and periodic error covers 30 arc seconds (15" P2P in one direction and 15" P2P - that is 30" of "travel"). If periodic error is perfectly smooth (saw tooth pattern) - each sub will have just under one pixel of elongation. That is not something that will be seen.

However - periodic error is not smooth and resembles more sine wave - which has parts where it changes slowly (at peak or trough) and slopes where it changes fast. At these fast changing points - error will be 2-3 times larger then average. 2-3 pixels of elongation will show.

So even with 15" P2P - some of 30s exposures will see some trailing, and it is not uncommon for EQ5, EQ6 and HEQ5 class mounts to have 30" P2P.