Sky-Watcher Star Adventurer - Tracking

[BigPaddy]

Hello Everyone !

This is my first post here.

My Name is Patrick and Im and amateur astro photographer but I have over 20 years of experience in the field of photography.  Im fine with wide field astro imaging but I have some problems with a more narrow field of view, or rather with tracking.

I bought my Sky Adventurer few weeks ago and I was using it recently for M31 images.

I can pull out 4 + minutes with wide angle shots. With 600mm on the other hand 30 sek is max I can track without seeing trailing. Last night I was able to get 1m exposure without seeing any massive star trails but taking shots in intervals showed 2 from 8 images were tracked kinda fine, the rest of them shows like the tracker tried but gave up during the process. Thats 80% of bad frames. ( Images attached )

My setup: Sky-Watcher Star Adventurer.

Camera: Sony A7R III

Lens: 200-300G

Other Eq: Wireless trigger on top of camera body.

Overall weight: 2.9kg

I polar aligned it 3 times and balanced it as best I could so there was no pulling when the cluthc was disabled. ( No wind, tripod knocks or other factors )

Is there anything Im doing wrong ? I would like to know some opinion and guidance if possible as Im new to trackers etc.

Thank you so much in advanced

Cheers

 

Edited August 24, 2020 by BigPaddy

[toxic]

hi BigPaddy  

when balancing you need to have the weighted end heavier while travelling up, and and lighter when travelling down so as to get rid of any back lash hope this helps but to be honest with you 600mm fl is asking a lot for the S A well most mounts really unguided to shoot at that F L then you need a guide scope and guide camera.

[Davey-T]

Hi Patrick and welcome to SGL.

Being mass produced the SWSA can be very variable in performance, I can do about 90 sec's reliably using a 300mm f/4 lens with APSC sensor, widefield with 14mm is pretty much open ended, 15 minutes easily.

You can do a test to see if the tracking speed is correct by setting it up indoors with a laser pointer mounted on the dovetail and marking the starting point then leaving it running for a sidereal day, 4 mins less than 24 hours to see if it ends up pointing at the same spot.

If thats fine check that the screws holding the dovetail clamp to the mount are tight as they can work loose.

Dave

Also it can depend whereabouts in the sky you are imaging.

Edited August 24, 2020 by Davey-T

[BigPaddy]

8 minutes ago, toxic said:

most mounts really unguided to shoot at that F L then you need a guide scope and guide camera.

Thank you so much toxic. Thats probably what I need.

Not only tracking is new for me but now I need a guiding scope to figure it out

Cheers

[BigPaddy]

6 minutes ago, Davey-T said:

You can do a test to see if the tracking speed is correct by setting it up indoors with a laser pointer mounted on the dovetail and marking the starting point then leaving it running for a sidereal day, 4 mins less than 24 hours to see if it ends up pointing at the same spot.
 

Thank you so much. So leave it running for same amount of time on 2 different days and compare travel distance ?

Cheers

[vlaiv]

Hi and welcome to SGL.

Once you move up in focal length, it becomes useful to start thinking in sampling rate rather than focal length. Sampling rate (or sometimes called camera constant and other names) - is amount of sky covered by single pixel. It is expressed in arc seconds per pixel.

For example, your camera has 4.5um pixel size, and there is simple formula to calculate sampling rate for your focal length:

which gives 1.55"/px for 600mm focal length.

1.55"/px is very serious sampling rate and here everything starts to show - wind, shakes, every glitch of the mount and optical aberrations of your lens.

In principle there are two major types of errors in mount that cause trailing -  polar alignment error and periodic error.

If you have rather good polar alignment - less than 1/5 of a degree out, you will have max drift of about 3.14"/minute. This means that in only one minute, your stars will have 2 pixel trails due to very good polar alignment.

On the other hand, periodic error is inherent in the mount due to manufacturing defects (there is no such thing as a perfect circle in engineering) and it can be as high as 30-40" peak to peak. This error repeats every 10 minutes, so there is at least 4"/minute trailing from periodic error - or even more. 

In any case, if you go with resolution below about 5-6"/px you are really in serious astrophotography waters and you want better mount or at least to start auto guiding.

 

[Davey-T]

Just now, BigPaddy said:

Thank you so much. So leave it running for same amount of time on 2 different days and compare travel distance ?

Cheers

No once is enough it should end up very close to the starting point.

I used a laser spirit level

Dave

 

[BigPaddy]

5 hours ago, vlaiv said:

In any case, if you go with resolution below about 5-6"/px you are really in serious astrophotography waters and you want better mount or at least to start auto guiding.

 

So it sounds like I need to look for some guiding scope and software then.

Thank you !

[vlaiv]

1 minute ago, BigPaddy said:

So it sounds like I need to look for some guiding scope and software then.

Thank you !

Do pay attention that star adventurer only allows for guiding in RA axis. This means that you'll be able to correct issues in RA but not in DEC - which are mostly down to polar alignment error (or wind / cable snag and such).

Have you examined your images above for direction?

Try to figure out which way is RA and which is DEC in your images (they are perpendicular to each other) and see if trailing coincides with either axis. That will tell you likely cause of trailing (either PA error or periodic error).

[Davey-T]

Used mine with 300mm without guiding as I prefer it to be a stand alone, grab and go setup, no computer involved.

I have got a guiding setup for it bur never actually used it 😁

Dave

[BigPaddy]

9 minutes ago, vlaiv said:

Have you examined your images above for direction?

Yes, the rotation occurs around polaris in 90% of my images.

[vlaiv]

2 minutes ago, BigPaddy said:

Yes, the rotation occurs around polaris in 90% of my images.

That would be RA direction - what you are seeing is periodic error then. Guiding should solve that.

Not sure if star adventurer has periodic error correction? It is one way of dealing with this issue - not perfect but it helps quite a bit sometimes. It basically means "recording" how your mount behaves as it sometimes leads and sometimes trails optimal tracking and then "playing back" those errors "in reverse" - when mount leads, periodic error correction slows it down just enough to balance things out and similarly if mount lags - it speeds it up again to balance tracking out.

 

[BigPaddy]

40 minutes ago, vlaiv said:

Guiding should solve that.

Its also not smooth, sometimes looks like dot and line and sometimes like 3 dots ( very jerky and non consistent ).

I will try to look for some guiding scopes and how dificult it is to make it work.

Edited August 24, 2020 by BigPaddy

[Gfamily]

I've not guided, but I'm pretty sure a friend with the SA used a 6x30 finder scope with an ASI 120 as the guide camera.

Mounted it on the counterweight bar and used it for 10 minute exposures using a 440mm scope and dSLR 

Edited August 24, 2020 by Gfamily

[BigPaddy]

I've done some quick reaserch and it looks I need:

ZWO ASI 120MC-S USB 3.0 + ZWO Mini Guide Scope 30mm f4

That should solve the issues I was having.

Correct me if Im wrong of course

[vlaiv]

42 minutes ago, BigPaddy said:

I've done some quick reaserch and it looks I need:

ZWO ASI 120MC-S USB 3.0 + ZWO Mini Guide Scope 30mm f4

That should solve the issues I was having.

Correct me if Im wrong of course

That will be ok. You'll need a computer/laptop with guiding software like PHD2 that will control everything.

If you don't want to use laptop in the field, you'll need to look at standalone auto guiding systems. There are a few popular ones - Synguider from SkyWatcher or Lacerta mgen II / III (newer model)

[BigPaddy]

1 hour ago, vlaiv said:

That will be ok. You'll need a computer/laptop with guiding software like PHD2 that will control everything.

Im happy with laptop as I need it for focusing anyway ( as for now )

Thank you so much !

[happy-kat]

You might find this thread interesting

https://stargazerslounge.com/topic/234107-anyone-using-cheap-windows-tablet-with-apt/