Aargh! Polar alignment!

[Icesheet]

This has been a nightmare imagkng season for me and I’ve actually gone backwards. So much so that I couldn’t even get polar alignment the other night and I have no idea why. 

 

I use a polemaster and other than getting used to the process it’s been great and I’ve never had any issues once I get everything set up.  However, the other night  I couldn’t even get exposures longer than 10sec without trailing. In fact I could see the stars were actually jumping between exposures. I didn’t do anything differently than I did before so I’m at a bit of a loss. I even took the mount off the tripod, levelled it, double checked balancing etc. Nothing helped, same outcome.

 

I’ve uploaded the video here, if you look closely you can see trailing is evident (10sec exposure) and the stars ‘jump’ position between exposures. Has anyone experienced this before? Could it be something to with the gears of the mount?

 

[david_taurus83]

Hi. I cant see any video? Theres a video embedded but it's not playing or displaying properly? Also, it might be more helpful if you tell us what gear you are using? Camera, scope, autoguiding, mount control?

[Icesheet]

Hmm, ok thanks for letting me know. It’s playing on my phone but I’ll upload it again on my laptop when I get home.

 

Sure, sorry about the equipment. That night Inwas shooting with a Samsung 135 and ZWO ASI1600mm on an HEQ5. No guiding as I presumed at such a wide angle I wouldn’t have any trouble ?

 

I suppose it’s even more worrying that at a focal length of 135mm there was noticeable trailing in 10sec exposures. 

[david_taurus83]

Sounds like the mount wasnt tracking?

[FaDG]

2 minutes ago, david_taurus83 said:

Sounds like the mount wasnt tracking?

Was going to ask the same question: did you Check that the mount was actually tracking and the tracking rate was sidereal? 

No way such a drift in 10" exposures @ 135mm could be caused by polar alignment. 

[Icesheet]

2 minutes ago, david_taurus83 said:

Sounds like the mount wasnt tracking?

That was one of my thoughts. I’m not sure how to diagnose that though?

[david_taurus83]

How did you align it initially? Are you using the hand controller?

[Icesheet]

Yep just using the hand controller. 

[Icesheet]

25 minutes ago, FaDG said:

Was going to ask the same question: did you Check that the mount was actually tracking and the tracking rate was sidereal? 

No way such a drift in 10" exposures @ 135mm could be caused by polar alignment. 

Sorry, didn’t see this. It was tracking yes, but I didn’t check it was sidereal to be honest. Didn’t think of that at the time. I hadn’t changed anything on the mount from my previous session though. I’ll check what the tracking mode is tomorrow. 

[Tomatobro]

You start polar alignment from the park position and use the handset to rotate the mount. Tracking should be off. Steve Richards has done a setup procedure which is downloadable as a PDF from Flo.

Follow the procedure and you should be ok

[david_taurus83]

I can see the video now. Its moving in the same direction it seems. At that focal length your image scale is around 5.81 arc seconds per pixel. From our perspective, stars appear to move across the sky at around 15 arc seconds every second of time. So the stars will trail across 2.5 pixels of your camera per second of time if it was static. I bet if you measure one of the stars it will be around 25 pixels across, indicating that the mount wasnt tracking at the time.

[spillage]

If you are using polemaster then it will not be a drastic PA issue. By the way don’t worry too much about the mount being level, this just helps with the orientation of adjustment whilst doing PA but with polemaster it will be easy enough.

[Icesheet]

Thanks all, seems the consensus is the mount was not tracking for whatever reason. I guess I’ll need to double check everything again next time I get a chance to get out. Thanks!

[ollypenrice]

On 20/03/2019 at 21:46, Icesheet said:

Thanks all, seems the consensus is the mount was not tracking for whatever reason. I guess I’ll need to double check everything again next time I get a chance to get out. Thanks!

The easy way to check this next time is to centre a bright star and then set the camera to do looping subs of 1 or 2 secs. If the star's moving the mount probably isn't tracking.

Olly

[George Gearless]

At the risk of being named 'captain obvious': did you check your clutches and screws?

Not long ago I had problems with my AZ Goto mount and couldn't figure out why. But while I cursing and swearing started to dismantle to move back inside, I heard the distinct clank of the mount rattling in its cradles on the tripod. The Allen screws were almost completely undone. It just never occured to me to check. Now I check every time :).

[Whistlin Bob]

2 hours ago, George Gearless said:

At the risk of being named 'captain obvious': did you check your clutches and screws?

More frequently than I'd like to admit imaging sessions go wrong precisely because I've missed an obvious step or done something daft 

My question is- is Captain Obvious real, and if so- how do I call him/her so that I can be saved occasionally from my own stupidity?

[Icesheet]

Thanks folks, some looping subs and a Captain Obvious checklist on my next venture out! 

[GraemeC]

 Movement in a short exposure image using a wide angle lens in unlikely to have anything to do with tracking.  I'd suggest the mount or tripod or clamping was unstable.  For example, the one and only time I used a ball socket clamp for a dslr seemed like a good idea until I realised the dslr was slowly drooping down.  Now I use ring clamps so the camera body and the camera lens are supported independently.

graeme