PHD - Trailing on the rhs of image

[swag72]

So, last night I got the guiding all working. I'm really very pleased with it. Sorry for the stupid PHD questions I asked though!! Anyway, I have another!!

I have trailing on the right hand side of the image, more towards the bottom half and corner. Everywhere else, the stars are nice and round - What has happened there? I am guessing it must be some setting, but not sure which! Also, once you have the settings set, does 'save' keep the settings? I don't see a load button though to be able to get them back again!

[Ant]

Thats probably not the guiding - if it were the guiding it would have affected all the stars...

Congratulations on getting 10 minutes

It could be a collimation issue, the camera may not be quite square in the focuser - I'm sure that there are other people who will know.

Cheers

Ant

[jgs001]

Nice one Sara... I'd guess the same as Ant... the camera isn't quite square, and it's not actually trailing, but odd out of focus...

Can you post the image and a crop of the rhs ?

[swag72]

How can the camera not be square in the focuser? Will post up an example in a bit.

[jgs001]

You'll be surprised how just a small fraction makes a big difference to the image. I hadn't tightened up the lock knob on the camera connection, and it was enough to allow the camera to twist ever so slightly in the focuser and that caused what you describe on the upper edge (lhs in my case) of the frame. I now use a screwdriver to lock it in firmly and don't see it anymore

[swag72]

This is the first time I have connected the camera without the screw thread reducer, instead using the turn screws into the focuser as I've got some different connections.. Mmm, will have to concentrate on that then tonight. Perhaps I'll stick the reducer back on so that it screws in square.

[davew]

Do you have a flattener / reducer ? The odd stars could be aberrations from the scope.

Dave.

[swag72]

I have got a reducer, but that takes the scope down to 765mm, for the first guiding test I wanted to max out the mm - hence camera stuck on the end! The trailing isn't odd stars, it's all the stars within a specific area of the image.

[davew]

If the reducer also flattens, using the scope for the first time without it may show as stretched stars in the corners. If it's worse in one corner we could be back to the camera not being square and making it look worse.

A picture and more info required.

Dave.

[davew]

Do your stars look like this in the corner ?

A sub showing the effects of not using a flattener. The centre stars were round.

Dave.

[martin_h]

I get exactly the same effect in the corners

[Whippy]

I have the same problem with my ZS66 and have put it down to the camera not being square onto the focus plane too.

From what I've read a good way of finding out woukd be to use a laser collimator in the focuser and if the laser point isn't in the middle of the objective lens at the front of the scope then that's most likely your problem.

Tony..

[swag72]

Please excuse the quality of the pic!!

Here's the rhs, going from the middle towards the bottom of the picture. The stars on the lhs and centre are nice and round.

[Whippy]

That looks a bit like field rotation to me. But if your stars on the other side of the image aren't doing the same then it probably isn't. Can you post the whole image?

Tony..

[swag72]

Sure - Here's the whole image.

[themos]

To isolate optics effects from tracking effects, point the setup towards Polaris and take a long exposure. Tracking won't matter there.

[Whippy]

I'm pretty certain that's field rotation Sara. See how the stars from the bottom left round to the top right kind of 'swirl'? That's normally a sign of it.

It normally happens when your mount isn't polar aligned well enough and it's more of a potential problem when you're imaging at longer focal lengths with long exposures.I think if you spent a bit of time getting the mount sorted, your stars wouldn't do that.

Tony..

[SteveP]

Swag

That looks like polar (aka field) rotation to me. There is evidence of it also in the top right and bottom left of M31. Note how it is centred on a point off of your image. That will be the position of your guidescope.

Don't worry though, it is cured by having a more accurate polar alignment

HTH

Steve

[swag72]

Yes I can see that now - So, how do I get a good polar alignment? I thought it was pretty good! Oh well, back to the drawing board I suppose!

[Psychobilly]

Yes I can see that now - So, how do I get a good polar alignment? I thought it was pretty good! Oh well, back to the drawing board I suppose!

Drift alignment with PHD assisting...?

[themos]

If you've taken a sequence, put it in DSS and attempt to stack it. Look at the offsets and angles DSS produces. If the angle increases with capture-time then it's field rotation.

[swag72]

Hey guys - This is getting more confusing by the minute!

[themos]

You need to quantify the problem: the pages here

On Polar Axis Alignment

have some calculators to help you.

[shaunster]

I use polar finder, works for me at 423mm, if your usign a longer focal lenght then drift alignment might be needed for long subs

I also tried a PHD drift alignment, it was very easy but takes a little time.

[swag72]

Thanks Thermos, but these equations assume a degree of knowledge that I do not have at the moment. For example, equation 1 - drift in arc seonds - How do I know what that is, where would I find it? That's just for starters!!

I only took my scope out of it's box a month ago!